@c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. @c Copyright (C) 1990--1995, 1998--1999, 2001--2021 Free Software @c Foundation, Inc. @c See the file elisp.texi for copying conditions. @node Windows @chapter Windows This chapter describes the functions and variables related to Emacs windows. @xref{Frames}, for how windows are assigned an area of screen available for Emacs to use. @xref{Display}, for information on how text is displayed in windows. @menu * Basic Windows:: Basic information on using windows. * Windows and Frames:: Relating windows to the frame they appear on. * Window Sizes:: Accessing a window's size. * Resizing Windows:: Changing the sizes of windows. * Preserving Window Sizes:: Preserving the size of windows. * Splitting Windows:: Creating a new window. * Deleting Windows:: Removing a window from its frame. * Recombining Windows:: Preserving the frame layout when splitting and deleting windows. * Selecting Windows:: The selected window is the one that you edit in. * Cyclic Window Ordering:: Moving around the existing windows. * Buffers and Windows:: Each window displays the contents of a buffer. * Switching Buffers:: Higher-level functions for switching to a buffer. * Displaying Buffers:: Displaying a buffer in a suitable window. * Window History:: Each window remembers the buffers displayed in it. * Dedicated Windows:: How to avoid displaying another buffer in a specific window. * Quitting Windows:: How to restore the state prior to displaying a buffer. * Side Windows:: Special windows on a frame's sides. * Atomic Windows:: Preserving parts of the window layout. * Window Point:: Each window has its own location of point. * Window Start and End:: Buffer positions indicating which text is on-screen in a window. * Textual Scrolling:: Moving text up and down through the window. * Vertical Scrolling:: Moving the contents up and down on the window. * Horizontal Scrolling:: Moving the contents sideways on the window. * Coordinates and Windows:: Converting coordinates to windows. * Mouse Window Auto-selection:: Automatically selecting windows with the mouse. * Window Configurations:: Saving and restoring the state of the screen. * Window Parameters:: Associating additional information with windows. * Window Hooks:: Hooks for scrolling, window size changes, redisplay going past a certain point, or window configuration changes. @end menu @node Basic Windows @section Basic Concepts of Emacs Windows @cindex window A @dfn{window} is an area of the screen that is used to display a buffer (@pxref{Buffers}). In Emacs Lisp, windows are represented by a special Lisp object type. @cindex multiple windows Windows are grouped into frames (@pxref{Frames}). Each frame contains at least one window; the user can subdivide it into multiple, non-overlapping windows to view several buffers at once. Lisp programs can use multiple windows for a variety of purposes. In Rmail, for example, you can view a summary of message titles in one window, and the contents of the selected message in another window. @cindex terminal screen @cindex screen of terminal Emacs uses the word ``window'' with a different meaning than in graphical desktop environments and window systems, such as the X Window System. When Emacs is run on X, each of its graphical X windows is an Emacs frame (containing one or more Emacs windows). When Emacs is run on a text terminal, the frame fills the entire terminal screen. @cindex tiled windows Unlike X windows, Emacs windows are @dfn{tiled}; they never overlap within the area of the frame. When a window is created, resized, or deleted, the change in window space is taken from or given to the adjacent windows, so that the total area of the frame is unchanged. @defun windowp object This function returns @code{t} if @var{object} is a window (whether or not it displays a buffer). Otherwise, it returns @code{nil}. @end defun @cindex live windows A @dfn{live window} is one that is actually displaying a buffer in a frame. @defun window-live-p object This function returns @code{t} if @var{object} is a live window and @code{nil} otherwise. A live window is one that displays a buffer. @end defun @cindex internal windows The windows in each frame are organized into a @dfn{window tree}. @xref{Windows and Frames}. The leaf nodes of each window tree are live windows---the ones actually displaying buffers. The internal nodes of the window tree are @dfn{internal windows}, which are not live. @cindex valid windows A @dfn{valid window} is one that is either live or internal. A valid window can be @dfn{deleted}, i.e., removed from its frame (@pxref{Deleting Windows}); then it is no longer valid, but the Lisp object representing it might be still referenced from other Lisp objects. A deleted window may be made valid again by restoring a saved window configuration (@pxref{Window Configurations}). You can distinguish valid windows from deleted windows with @code{window-valid-p}. @defun window-valid-p object This function returns @code{t} if @var{object} is a live window, or an internal window in a window tree. Otherwise, it returns @code{nil}, including for the case where @var{object} is a deleted window. @end defun @cindex selected window @cindex window selected within a frame In each frame, at any time, exactly one Emacs window is designated as @dfn{selected within the frame}. For the selected frame, that window is called the @dfn{selected window}---the one in which most editing takes place, and in which the cursor for selected windows appears (@pxref{Cursor Parameters}). Keyboard input that inserts or deletes text is also normally directed to this window. The selected window's buffer is usually also the current buffer, except when @code{set-buffer} has been used (@pxref{Current Buffer}). As for non-selected frames, the window selected within the frame becomes the selected window if the frame is ever selected. @xref{Selecting Windows}. @defun selected-window This function returns the selected window (which is always a live window). @end defun @anchor{Window Group}Sometimes several windows collectively and cooperatively display a buffer, for example, under the management of Follow Mode (@pxref{Follow Mode,,, emacs}), where the windows together display a bigger portion of the buffer than one window could alone. It is often useful to consider such a @dfn{window group} as a single entity. Several functions such as @code{window-group-start} (@pxref{Window Start and End}) allow you to do this by supplying, as an argument, one of the windows as a stand in for the whole group. @defun selected-window-group @vindex selected-window-group-function When the selected window is a member of a group of windows, this function returns a list of the windows in the group, ordered such that the first window in the list is displaying the earliest part of the buffer, and so on. Otherwise the function returns a list containing just the selected window. The selected window is considered part of a group when the buffer local variable @code{selected-window-group-function} is set to a function. In this case, @code{selected-window-group} calls it with no arguments and returns its result (which should be the list of windows in the group). @end defun @node Windows and Frames @section Windows and Frames Each window belongs to exactly one frame (@pxref{Frames}). @defun window-frame &optional window This function returns the frame that the window @var{window} belongs to. If @var{window} is @code{nil}, it defaults to the selected window. @end defun @defun window-list &optional frame minibuffer window This function returns a list of live windows belonging to the frame @var{frame}. If @var{frame} is omitted or @code{nil}, it defaults to the selected frame. The optional argument @var{minibuffer} specifies whether to include the minibuffer window in the returned list. If @var{minibuffer} is @code{t}, the minibuffer window is included. If @var{minibuffer} is @code{nil} or omitted, the minibuffer window is included only if it is active. If @var{minibuffer} is neither @code{nil} nor @code{t}, the minibuffer window is never included. The optional argument @var{window}, if non-@code{nil}, should be a live window on the specified frame; then @var{window} will be the first element in the returned list. If @var{window} is omitted or @code{nil}, the window selected within the frame is the first element. @end defun @cindex window tree @cindex root window Windows in the same frame are organized into a @dfn{window tree}, whose leaf nodes are the live windows. The internal nodes of a window tree are not live; they exist for the purpose of organizing the relationships between live windows. The root node of a window tree is called the @dfn{root window}. It can be either a live window (if the frame has just one window), or an internal window. A minibuffer window (@pxref{Minibuffer Windows}) that is not alone on its frame does not have a parent window, so it strictly speaking is not part of its frame's window tree. Nonetheless, it is a sibling window of the frame's root window, and thus can be reached via @code{window-next-sibling}. Also, the function @code{window-tree} described at the end of this section lists the minibuffer window alongside the actual window tree. @defun frame-root-window &optional frame-or-window This function returns the root window for @var{frame-or-window}. The argument @var{frame-or-window} should be either a window or a frame; if omitted or @code{nil}, it defaults to the selected frame. If @var{frame-or-window} is a window, the return value is the root window of that window's frame. @end defun @cindex parent window @cindex child window @cindex sibling window When a window is split, there are two live windows where previously there was one. One of these is represented by the same Lisp window object as the original window, and the other is represented by a newly-created Lisp window object. Both of these live windows become leaf nodes of the window tree, as @dfn{child windows} of a single internal window. If necessary, Emacs automatically creates this internal window, which is also called the @dfn{parent window}, and assigns it to the appropriate position in the window tree. A set of windows that share the same parent are called @dfn{siblings}. @cindex parent window @defun window-parent &optional window This function returns the parent window of @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. The return value is @code{nil} if @var{window} has no parent (i.e., it is a minibuffer window or the root window of its frame). @end defun Each internal window always has at least two child windows. If this number falls to one as a result of window deletion, Emacs automatically deletes the internal window, and its sole remaining child window takes its place in the window tree. Each child window can be either a live window, or an internal window (which in turn would have its own child windows). Therefore, each internal window can be thought of as occupying a certain rectangular @dfn{screen area}---the union of the areas occupied by the live windows that are ultimately descended from it. @cindex window combination @cindex vertical combination @cindex horizontal combination For each internal window, the screen areas of the immediate children are arranged either vertically or horizontally (never both). If the child windows are arranged one above the other, they are said to form a @dfn{vertical combination}; if they are arranged side by side, they are said to form a @dfn{horizontal combination}. Consider the following example: @smallexample @group ______________________________________ | ______ ____________________________ | || || __________________________ || || ||| ||| || ||| ||| || ||| ||| || |||____________W4____________||| || || __________________________ || || ||| ||| || ||| ||| || |||____________W5____________||| ||__W2__||_____________W3_____________ | |__________________W1__________________| @end group @end smallexample @noindent The root window of this frame is an internal window, @var{W1}. Its child windows form a horizontal combination, consisting of the live window @var{W2} and the internal window @var{W3}. The child windows of @var{W3} form a vertical combination, consisting of the live windows @var{W4} and @var{W5}. Hence, the live windows in this window tree are @var{W2}, @var{W4}, and @var{W5}. The following functions can be used to retrieve a child window of an internal window, and the siblings of a child window. @defun window-top-child &optional window This function returns the topmost child window of @var{window}, if @var{window} is an internal window whose children form a vertical combination. For any other type of window, the return value is @code{nil}. @end defun @defun window-left-child &optional window This function returns the leftmost child window of @var{window}, if @var{window} is an internal window whose children form a horizontal combination. For any other type of window, the return value is @code{nil}. @end defun @defun window-child window This function returns the first child window of the internal window @var{window}---the topmost child window for a vertical combination, or the leftmost child window for a horizontal combination. If @var{window} is a live window, the return value is @code{nil}. @end defun @defun window-combined-p &optional window horizontal This function returns a non-@code{nil} value if and only if @var{window} is part of a vertical combination. If @var{window} is omitted or @code{nil}, it defaults to the selected one. If the optional argument @var{horizontal} is non-@code{nil}, this means to return non-@code{nil} if and only if @var{window} is part of a horizontal combination. @end defun @defun window-next-sibling &optional window This function returns the next sibling of the window @var{window}. If omitted or @code{nil}, @var{window} defaults to the selected window. The return value is @code{nil} if @var{window} is the last child of its parent. @end defun @defun window-prev-sibling &optional window This function returns the previous sibling of the window @var{window}. If omitted or @code{nil}, @var{window} defaults to the selected window. The return value is @code{nil} if @var{window} is the first child of its parent. @end defun The functions @code{window-next-sibling} and @code{window-prev-sibling} should not be confused with the functions @code{next-window} and @code{previous-window}, which return the next and previous window, respectively, in the cyclic ordering of windows (@pxref{Cyclic Window Ordering}). The following functions can be useful to locate a window within its frame. @defun frame-first-window &optional frame-or-window This function returns the live window at the upper left corner of the frame specified by @var{frame-or-window}. The argument @var{frame-or-window} must denote a window or a live frame and defaults to the selected frame. If @var{frame-or-window} specifies a window, this function returns the first window on that window's frame. Under the assumption that the frame from our canonical example is selected @code{(frame-first-window)} returns @var{W2}. @end defun @defun window-at-side-p &optional window side This function returns @code{t} if @var{window} is located at @var{side} of its containing frame. The argument @var{window} must be a valid window and defaults to the selected one. The argument @var{side} can be any of the symbols @code{left}, @code{top}, @code{right} or @code{bottom}. The default value @code{nil} is handled like @code{bottom}. Note that this function disregards the minibuffer window (@pxref{Minibuffer Windows}). Hence, with @var{side} equal to @code{bottom} it may return @code{t} also when the minibuffer window appears right below @var{window}. @end defun @cindex window in direction @defun window-in-direction direction &optional window ignore sign wrap minibuf This function returns the nearest live window in direction @var{direction} as seen from the position of @code{window-point} in window @var{window}. The argument @var{direction} must be one of @code{above}, @code{below}, @code{left} or @code{right}. The optional argument @var{window} must denote a live window and defaults to the selected one. This function does not return a window whose @code{no-other-window} parameter is non-@code{nil} (@pxref{Window Parameters}). If the nearest window's @code{no-other-window} parameter is non-@code{nil}, this function tries to find another window in the indicated direction whose @code{no-other-window} parameter is @code{nil}. If the optional argument @var{ignore} is non-@code{nil}, a window may be returned even if its @code{no-other-window} parameter is non-@code{nil}. If the optional argument @var{sign} is a negative number, it means to use the right or bottom edge of @var{window} as reference position instead of @code{window-point}. If @var{sign} is a positive number, it means to use the left or top edge of @var{window} as reference position. If the optional argument @var{wrap} is non-@code{nil}, this means to wrap @var{direction} around frame borders. For example, if @var{window} is at the top of the frame and @var{direction} is @code{above}, then this function usually returns the frame's minibuffer window if it's active and a window at the bottom of the frame otherwise. If the optional argument @var{minibuf} is @code{t}, this function may return the minibuffer window even when it's not active. If the optional argument @var{minibuf} is @code{nil}, this means to return the minibuffer window if and only if it is currently active. If @var{minibuf} is neither @code{nil} nor @code{t}, this function never returns the minibuffer window. However, if @var{wrap} is non-@code{nil}, it always acts as if @var{minibuf} were @code{nil}. If it doesn't find a suitable window, this function returns @code{nil}. Don't use this function to check whether there is @emph{no} window in @var{direction}. Calling @code{window-at-side-p} described above is a much more efficient way to do that. @end defun The following function allows the entire window tree of a frame to be retrieved: @defun window-tree &optional frame This function returns a list representing the window tree for frame @var{frame}. If @var{frame} is omitted or @code{nil}, it defaults to the selected frame. The return value is a list of the form @code{(@var{root} @var{mini})}, where @var{root} represents the window tree of the frame's root window, and @var{mini} is the frame's minibuffer window. If the root window is live, @var{root} is that window itself. Otherwise, @var{root} is a list @code{(@var{dir} @var{edges} @var{w1} @var{w2} ...)} where @var{dir} is @code{nil} for a horizontal combination and @code{t} for a vertical combination, @var{edges} gives the size and position of the combination, and the remaining elements are the child windows. Each child window may again be a window object (for a live window) or a list with the same format as above (for an internal window). The @var{edges} element is a list @code{(@var{left} @var{top} @var{right} @var{bottom})}, similar to the value returned by @code{window-edges} (@pxref{Coordinates and Windows}). @end defun @node Window Sizes @section Window Sizes @cindex window size @cindex size of window The following schematic shows the structure of a live window: @smallexample @group ____________________________________________ |______________ Header Line ______________|RD| ^ ^ |LS|LM|LF| |RF|RM|RS| | | | | | | | | | | | | | Window | | | | Text Area | | | | | Window Body | | | | | (Window Body) | | | | | Total Height | | | | | | | | | Height | | | | |<- Window Body Width ->| | | | | | v |__|__|__|_______________________|__|__|__| | | |_________ Horizontal Scroll Bar _________| | | |_______________ Mode Line _______________|__| | |_____________ Bottom Divider _______________| v <---------- Window Total Width ------------> @end group @end smallexample @cindex window body @cindex text area of a window @cindex body of a window At the center of the window is the @dfn{text area}, or @dfn{body}, where the buffer text is displayed. The text area can be surrounded by a series of optional areas. On the left and right, from innermost to outermost, these are the left and right fringes, denoted by LF and RF (@pxref{Fringes}); the left and right margins, denoted by LM and RM in the schematic (@pxref{Display Margins}); the left or right vertical scroll bar, only one of which is present at any time, denoted by LS and RS (@pxref{Scroll Bars}); and the right divider, denoted by RD (@pxref{Window Dividers}). At the top of the window is the header line (@pxref{Header Lines}). At the bottom of the window are the horizontal scroll bar (@pxref{Scroll Bars}); the mode line (@pxref{Mode Line Format}); and the bottom divider (@pxref{Window Dividers}). Emacs provides miscellaneous functions for finding the height and width of a window. The return value of many of these functions can be specified either in units of pixels or in units of lines and columns. On a graphical display, the latter actually correspond to the height and width of a default character specified by the frame's default font as returned by @code{frame-char-height} and @code{frame-char-width} (@pxref{Frame Font}). Thus, if a window is displaying text with a different font or size, the reported line height and column width for that window may differ from the actual number of text lines or columns displayed within it. @cindex window height @cindex height of a window @cindex total height of a window The @dfn{total height} of a window is the number of lines comprising the window's body, the header line, the horizontal scroll bar, the mode line and the bottom divider (if any). @defun window-total-height &optional window round This function returns the total height, in lines, of the window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. If @var{window} is an internal window, the return value is the total height occupied by its descendant windows. If a window's pixel height is not an integral multiple of its frame's default character height, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total heights of all its child windows internally equals the total height of their parent. This means that although two windows have the same pixel height, their internal total heights may differ by one line. This means also, that if window is vertically combined and has a next sibling, the topmost row of that sibling can be calculated as the sum of this window's topmost row and total height (@pxref{Coordinates and Windows}) If the optional argument @var{round} is @code{ceiling}, this function returns the smallest integer larger than @var{window}'s pixel height divided by the character height of its frame; if it is @code{floor}, it returns the largest integer smaller than said value; with any other @var{round} it returns the internal value of @var{windows}'s total height. @end defun @cindex window width @cindex width of a window @cindex total width of a window The @dfn{total width} of a window is the number of lines comprising the window's body, its margins, fringes, scroll bars and a right divider (if any). @defun window-total-width &optional window round This function returns the total width, in columns, of the window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. If @var{window} is internal, the return value is the total width occupied by its descendant windows. If a window's pixel width is not an integral multiple of its frame's character width, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total widths of all its children internally equals the total width of their parent. This means that although two windows have the same pixel width, their internal total widths may differ by one column. This means also, that if this window is horizontally combined and has a next sibling, the leftmost column of that sibling can be calculated as the sum of this window's leftmost column and total width (@pxref{Coordinates and Windows}). The optional argument @var{round} behaves as it does for @code{window-total-height}. @end defun @defun window-total-size &optional window horizontal round This function returns either the total height in lines or the total width in columns of the window @var{window}. If @var{horizontal} is omitted or @code{nil}, this is equivalent to calling @code{window-total-height} for @var{window}; otherwise it is equivalent to calling @code{window-total-width} for @var{window}. The optional argument @var{round} behaves as it does for @code{window-total-height}. @end defun The following two functions can be used to return the total size of a window in units of pixels. @cindex window pixel height @cindex pixel height of a window @cindex total pixel height of a window @defun window-pixel-height &optional window This function returns the total height of window @var{window} in pixels. @var{window} must be a valid window and defaults to the selected one. The return value includes mode and header line, a horizontal scroll bar and a bottom divider, if any. If @var{window} is an internal window, its pixel height is the pixel height of the screen areas spanned by its children. @end defun @cindex window pixel width @cindex pixel width of a window @cindex total pixel width of a window @defun window-pixel-width &optional window This function returns the width of window @var{window} in pixels. @var{window} must be a valid window and defaults to the selected one. The return value includes the fringes and margins of @var{window} as well as any vertical dividers or scroll bars belonging to @var{window}. If @var{window} is an internal window, its pixel width is the width of the screen areas spanned by its children. @end defun @cindex full-width window @cindex full-height window The following functions can be used to determine whether a given window has any adjacent windows. @defun window-full-height-p &optional window This function returns non-@code{nil} if @var{window} has no other window above or below it in its frame. More precisely, this means that the total height of @var{window} equals the total height of the root window on that frame. The minibuffer window does not count in this regard. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end defun @defun window-full-width-p &optional window This function returns non-@code{nil} if @var{window} has no other window to the left or right in its frame, i.e., its total width equals that of the root window on that frame. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end defun @cindex window body height @cindex body height of a window The @dfn{body height} of a window is the height of its text area, which does not include a mode or header line, a horizontal scroll bar, or a bottom divider. @defun window-body-height &optional window pixelwise This function returns the height, in lines, of the body of window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window; otherwise it must be a live window. If the optional argument @var{pixelwise} is non-@code{nil}, this function returns the body height of @var{window} counted in pixels. If @var{pixelwise} is @code{nil}, the return value is rounded down to the nearest integer, if necessary. This means that if a line at the bottom of the text area is only partially visible, that line is not counted. It also means that the height of a window's body can never exceed its total height as returned by @code{window-total-height}. @end defun @cindex window body width @cindex body width of a window The @dfn{body width} of a window is the width of its text area, which does not include the scroll bar, fringes, margins or a right divider. Note that when one or both fringes are removed (by setting their width to zero), the display engine reserves two character cells, one on each side of the window, for displaying the continuation and truncation glyphs, which leaves 2 columns less for text display. (The function @code{window-max-chars-per-line}, described below, takes this peculiarity into account.) @defun window-body-width &optional window pixelwise This function returns the width, in columns, of the body of window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window; otherwise it must be a live window. If the optional argument @var{pixelwise} is non-@code{nil}, this function returns the body width of @var{window} in units of pixels. If @var{pixelwise} is @code{nil}, the return value is rounded down to the nearest integer, if necessary. This means that if a column on the right of the text area is only partially visible, that column is not counted. It also means that the width of a window's body can never exceed its total width as returned by @code{window-total-width}. @end defun @cindex window body size @cindex body size of a window @defun window-body-size &optional window horizontal pixelwise This function returns the body height or body width of @var{window}. If @var{horizontal} is omitted or @code{nil}, it is equivalent to calling @code{window-body-height} for @var{window}; otherwise it is equivalent to calling @code{window-body-width}. In either case, the optional argument @var{pixelwise} is passed to the function called. @end defun For compatibility with previous versions of Emacs, @code{window-height} is an alias for @code{window-total-height}, and @code{window-width} is an alias for @code{window-body-width}. These aliases are considered obsolete and will be removed in the future. The pixel heights of a window's mode and header line can be retrieved with the functions given below. Their return value is usually accurate unless the window has not been displayed before: In that case, the return value is based on an estimate of the font used for the window's frame. @defun window-mode-line-height &optional window This function returns the height in pixels of @var{window}'s mode line. @var{window} must be a live window and defaults to the selected one. If @var{window} has no mode line, the return value is zero. @end defun @defun window-header-line-height &optional window This function returns the height in pixels of @var{window}'s header line. @var{window} must be a live window and defaults to the selected one. If @var{window} has no header line, the return value is zero. @end defun Functions for retrieving the height and/or width of window dividers (@pxref{Window Dividers}), fringes (@pxref{Fringes}), scroll bars (@pxref{Scroll Bars}), and display margins (@pxref{Display Margins}) are described in the corresponding sections. If your Lisp program needs to make layout decisions, you will find the following function useful: @defun window-max-chars-per-line &optional window face This function returns the number of characters displayed in the specified face @var{face} in the specified window @var{window} (which must be a live window). If @var{face} was remapped (@pxref{Face Remapping}), the information is returned for the remapped face. If omitted or @code{nil}, @var{face} defaults to the default face, and @var{window} defaults to the selected window. Unlike @code{window-body-width}, this function accounts for the actual size of @var{face}'s font, instead of working in units of the canonical character width of @var{window}'s frame (@pxref{Frame Font}). It also accounts for space used by the continuation glyph, if @var{window} lacks one or both of its fringes. @end defun @cindex fixed-size window @vindex window-min-height @vindex window-min-width Commands that change the size of windows (@pxref{Resizing Windows}), or split them (@pxref{Splitting Windows}), obey the variables @code{window-min-height} and @code{window-min-width}, which specify the smallest allowable window height and width. They also obey the variable @code{window-size-fixed}, with which a window can be @dfn{fixed} in size (@pxref{Preserving Window Sizes}). @defopt window-min-height This option specifies the minimum total height, in lines, of any window. Its value has to accommodate at least one text line as well as a mode and header line, a horizontal scroll bar and a bottom divider, if present. @end defopt @defopt window-min-width This option specifies the minimum total width, in columns, of any window. Its value has to accommodate two text columns as well as margins, fringes, a scroll bar and a right divider, if present. @end defopt The following function tells how small a specific window can get taking into account the sizes of its areas and the values of @code{window-min-height}, @code{window-min-width} and @code{window-size-fixed} (@pxref{Preserving Window Sizes}). @defun window-min-size &optional window horizontal ignore pixelwise This function returns the minimum size of @var{window}. @var{window} must be a valid window and defaults to the selected one. The optional argument @var{horizontal} non-@code{nil} means to return the minimum number of columns of @var{window}; otherwise return the minimum number of @var{window}'s lines. The return value makes sure that all components of @var{window} remain fully visible if @var{window}'s size were actually set to it. With @var{horizontal} @code{nil} it includes the mode and header line, the horizontal scroll bar and the bottom divider, if present. With @var{horizontal} non-@code{nil} it includes the margins and fringes, the vertical scroll bar and the right divider, if present. The optional argument @var{ignore}, if non-@code{nil}, means ignore restrictions imposed by fixed size windows, @code{window-min-height} or @code{window-min-width} settings. If @var{ignore} equals @code{safe}, live windows may get as small as @code{window-safe-min-height} lines and @code{window-safe-min-width} columns. If @var{ignore} is a window, ignore restrictions for that window only. Any other non-@code{nil} value means ignore all of the above restrictions for all windows. The optional argument @var{pixelwise} non-@code{nil} means to return the minimum size of @var{window} counted in pixels. @end defun @node Resizing Windows @section Resizing Windows @cindex window resizing @cindex resize window @cindex changing window size @cindex window size, changing This section describes functions for resizing a window without changing the size of its frame. Because live windows do not overlap, these functions are meaningful only on frames that contain two or more windows: resizing a window also changes the size of a neighboring window. If there is just one window on a frame, its size cannot be changed except by resizing the frame (@pxref{Frame Size}). Except where noted, these functions also accept internal windows as arguments. Resizing an internal window causes its child windows to be resized to fit the same space. @defun window-resizable window delta &optional horizontal ignore pixelwise This function returns @var{delta} if the size of @var{window} can be changed vertically by @var{delta} lines. If the optional argument @var{horizontal} is non-@code{nil}, it instead returns @var{delta} if @var{window} can be resized horizontally by @var{delta} columns. It does not actually change the window size. If @var{window} is @code{nil}, it defaults to the selected window. A positive value of @var{delta} means to check whether the window can be enlarged by that number of lines or columns; a negative value of @var{delta} means to check whether the window can be shrunk by that many lines or columns. If @var{delta} is non-zero, a return value of 0 means that the window cannot be resized. Normally, the variables @code{window-min-height} and @code{window-min-width} specify the smallest allowable window size (@pxref{Window Sizes}). However, if the optional argument @var{ignore} is non-@code{nil}, this function ignores @code{window-min-height} and @code{window-min-width}, as well as @code{window-size-fixed}. Instead, it considers the minimum-height window to be one consisting of a header and a mode line, a horizontal scrollbar and a bottom divider (if any), plus a text area one line tall; and a minimum-width window as one consisting of fringes, margins, a scroll bar and a right divider (if any), plus a text area two columns wide. If the optional argument @var{pixelwise} is non-@code{nil}, @var{delta} is interpreted as pixels. @end defun @defun window-resize window delta &optional horizontal ignore pixelwise This function resizes @var{window} by @var{delta} increments. If @var{horizontal} is @code{nil}, it changes the height by @var{delta} lines; otherwise, it changes the width by @var{delta} columns. A positive @var{delta} means to enlarge the window, and a negative @var{delta} means to shrink it. If @var{window} is @code{nil}, it defaults to the selected window. If the window cannot be resized as demanded, an error is signaled. The optional argument @var{ignore} has the same meaning as for the function @code{window-resizable} above. If the optional argument @var{pixelwise} is non-@code{nil}, @var{delta} will be interpreted as pixels. The choice of which window edges this function alters depends on the values of the option @code{window-combination-resize} and the combination limits of the involved windows; in some cases, it may alter both edges. @xref{Recombining Windows}. To resize by moving only the bottom or right edge of a window, use the function @code{adjust-window-trailing-edge}. @end defun @c The commands enlarge-window, enlarge-window-horizontally, @c shrink-window, and shrink-window-horizontally are documented in the @c Emacs manual. They are not preferred for calling from Lisp. @defun adjust-window-trailing-edge window delta &optional horizontal pixelwise This function moves @var{window}'s bottom edge by @var{delta} lines. If optional argument @var{horizontal} is non-@code{nil}, it instead moves the right edge by @var{delta} columns. If @var{window} is @code{nil}, it defaults to the selected window. If the optional argument @var{pixelwise} is non-@code{nil}, @var{delta} is interpreted as pixels. A positive @var{delta} moves the edge downwards or to the right; a negative @var{delta} moves it upwards or to the left. If the edge cannot be moved as far as specified by @var{delta}, this function moves it as far as possible but does not signal an error. This function tries to resize windows adjacent to the edge that is moved. If this is not possible for some reason (e.g., if that adjacent window is fixed-size), it may resize other windows. @end defun @cindex pixelwise, resizing windows @defopt window-resize-pixelwise If the value of this option is non-@code{nil}, Emacs resizes windows in units of pixels. This currently affects functions like @code{split-window} (@pxref{Splitting Windows}), @code{maximize-window}, @code{minimize-window}, @code{fit-window-to-buffer}, @code{fit-frame-to-buffer} and @code{shrink-window-if-larger-than-buffer} (all listed below). Note that when a frame's pixel size is not a multiple of its character size, at least one window may get resized pixelwise even if this option is @code{nil}. The default value is @code{nil}. @end defopt The following commands resize windows in more specific ways. When called interactively, they act on the selected window. @deffn Command fit-window-to-buffer &optional window max-height min-height max-width min-width preserve-size This command adjusts the height or width of @var{window} to fit the text in it. It returns non-@code{nil} if it was able to resize @var{window}, and @code{nil} otherwise. If @var{window} is omitted or @code{nil}, it defaults to the selected window. Otherwise, it should be a live window. If @var{window} is part of a vertical combination, this function adjusts @var{window}'s height. The new height is calculated from the actual height of the accessible portion of its buffer. The optional argument @var{max-height}, if non-@code{nil}, specifies the maximum total height that this function can give @var{window}. The optional argument @var{min-height}, if non-@code{nil}, specifies the minimum total height that it can give, which overrides the variable @code{window-min-height}. Both @var{max-height} and @var{min-height} are specified in lines and include mode and header line and a bottom divider, if any. If @var{window} is part of a horizontal combination and the value of the option @code{fit-window-to-buffer-horizontally} (see below) is non-@code{nil}, this function adjusts @var{window}'s width. The new width of @var{window} is calculated from the maximum length of its buffer's lines that follow the current start position of @var{window}. The optional argument @var{max-width} specifies a maximum width and defaults to the width of @var{window}'s frame. The optional argument @var{min-width} specifies a minimum width and defaults to @code{window-min-width}. Both @var{max-width} and @var{min-width} are specified in columns and include fringes, margins and scrollbars, if any. The optional argument @var{preserve-size}, if non-@code{nil}, will install a parameter to preserve the size of @var{window} during future resize operations (@pxref{Preserving Window Sizes}). If the option @code{fit-frame-to-buffer} (see below) is non-@code{nil}, this function will try to resize the frame of @var{window} to fit its contents by calling @code{fit-frame-to-buffer} (see below). @end deffn @defopt fit-window-to-buffer-horizontally If this is non-@code{nil}, @code{fit-window-to-buffer} can resize windows horizontally. If this is @code{nil} (the default) @code{fit-window-to-buffer} never resizes windows horizontally. If this is @code{only}, it can resize windows horizontally only. Any other value means @code{fit-window-to-buffer} can resize windows in both dimensions. @end defopt @defopt fit-frame-to-buffer If this option is non-@code{nil}, @code{fit-window-to-buffer} can fit a frame to its buffer. A frame is fit if and only if its root window is a live window and this option is non-@code{nil}. If this is @code{horizontally}, frames are fit horizontally only. If this is @code{vertically}, frames are fit vertically only. Any other non-@code{nil} value means frames can be resized in both dimensions. @end defopt If you have a frame that displays only one window, you can fit that frame to its buffer using the command @code{fit-frame-to-buffer}. @deffn Command fit-frame-to-buffer &optional frame max-height min-height max-width min-width only This command adjusts the size of @var{frame} to display the contents of its buffer exactly. @var{frame} can be any live frame and defaults to the selected one. Fitting is done only if @var{frame}'s root window is live. The arguments @var{max-height}, @var{min-height}, @var{max-width} and @var{min-width} specify bounds on the new total size of @var{frame}'s root window. @var{min-height} and @var{min-width} default to the values of @code{window-min-height} and @code{window-min-width} respectively. If the optional argument @var{only} is @code{vertically}, this function may resize the frame vertically only. If @var{only} is @code{horizontally}, it may resize the frame horizontally only. @end deffn The behavior of @code{fit-frame-to-buffer} can be controlled with the help of the two options listed next. @defopt fit-frame-to-buffer-margins This option can be used to specify margins around frames to be fit by @code{fit-frame-to-buffer}. Such margins can be useful to avoid, for example, that the resized frame overlaps the taskbar or parts of its parent frame. It specifies the numbers of pixels to be left free on the left, above, the right, and below a frame that shall be fit. The default specifies @code{nil} for each which means to use no margins. The value specified here can be overridden for a specific frame by that frame's @code{fit-frame-to-buffer-margins} parameter, if present. @end defopt @defopt fit-frame-to-buffer-sizes This option specifies size boundaries for @code{fit-frame-to-buffer}. It specifies the total maximum and minimum lines and maximum and minimum columns of the root window of any frame that shall be fit to its buffer. If any of these values is non-@code{nil}, it overrides the corresponding argument of @code{fit-frame-to-buffer}. @end defopt @deffn Command shrink-window-if-larger-than-buffer &optional window This command attempts to reduce @var{window}'s height as much as possible while still showing its full buffer, but no less than @code{window-min-height} lines. The return value is non-@code{nil} if the window was resized, and @code{nil} otherwise. If @var{window} is omitted or @code{nil}, it defaults to the selected window. Otherwise, it should be a live window. This command does nothing if the window is already too short to display all of its buffer, or if any of the buffer is scrolled off-screen, or if the window is the only live window in its frame. This command calls @code{fit-window-to-buffer} (see above) to do its work. @end deffn @cindex balancing window sizes @deffn Command balance-windows &optional window-or-frame This function balances windows in a way that gives more space to full-width and/or full-height windows. If @var{window-or-frame} specifies a frame, it balances all windows on that frame. If @var{window-or-frame} specifies a window, it balances only that window and its siblings (@pxref{Windows and Frames}). @end deffn @deffn Command balance-windows-area This function attempts to give all windows on the selected frame approximately the same share of the screen area. Full-width or full-height windows are not given more space than other windows. @end deffn @cindex maximizing windows @deffn Command maximize-window &optional window This function attempts to make @var{window} as large as possible, in both dimensions, without resizing its frame or deleting other windows. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end deffn @cindex minimizing windows @deffn Command minimize-window &optional window This function attempts to make @var{window} as small as possible, in both dimensions, without deleting it or resizing its frame. If @var{window} is omitted or @code{nil}, it defaults to the selected window. @end deffn @node Preserving Window Sizes @section Preserving Window Sizes @cindex preserving window sizes A window can get resized explicitly by using one of the functions from the preceding section or implicitly, for example, when resizing an adjacent window, when splitting or deleting a window (@pxref{Splitting Windows}, @pxref{Deleting Windows}) or when resizing the window's frame (@pxref{Frame Size}). It is possible to avoid implicit resizing of a specific window when there are one or more other resizable windows on the same frame. For this purpose, Emacs must be advised to @dfn{preserve} the size of that window. There are two basic ways to do that. @defvar window-size-fixed If this buffer-local variable is non-@code{nil}, the size of any window displaying the buffer cannot normally be changed. Deleting a window or changing the frame's size may still change the window's size, if there is no choice. If the value is @code{height}, then only the window's height is fixed; if the value is @code{width}, then only the window's width is fixed. Any other non-@code{nil} value fixes both the width and the height. If this variable is @code{nil}, this does not necessarily mean that any window showing the buffer can be resized in the desired direction. To determine that, use the function @code{window-resizable}. @xref{Resizing Windows}. @end defvar Often @code{window-size-fixed} is overly aggressive because it inhibits any attempt to explicitly resize or split an affected window as well. This may even happen after the window has been resized implicitly, for example, when deleting an adjacent window or resizing the window's frame. The following function tries hard to never disallow resizing such a window explicitly: @defun window-preserve-size &optional window horizontal preserve This function (un-)marks the height of window @var{window} as preserved for future resize operations. @var{window} must be a live window and defaults to the selected one. If the optional argument @var{horizontal} is non-@code{nil}, it (un-)marks the width of @var{window} as preserved. If the optional argument @var{preserve} is @code{t}, this means to preserve the current height/width of @var{window}'s body. The height/width of @var{window} will change only if Emacs has no better choice. Resizing a window whose height/width is preserved by this function never throws an error. If @var{preserve} is @code{nil}, this means to stop preserving the height/width of @var{window}, lifting any respective restraint induced by a previous call of this function for @var{window}. Calling @code{enlarge-window}, @code{shrink-window} or @code{fit-window-to-buffer} with @var{window} as argument may also remove the respective restraint. @end defun @code{window-preserve-size} is currently invoked by the following functions: @table @code @item fit-window-to-buffer If the optional argument @var{preserve-size} of that function (@pxref{Resizing Windows}) is non-@code{nil}, the size established by that function is preserved. @item display-buffer If the @var{alist} argument of that function (@pxref{Choosing Window}) contains a @code{preserve-size} entry, the size of the window produced by that function is preserved. @end table @code{window-preserve-size} installs a window parameter (@pxref{Window Parameters}) called @code{window-preserved-size} which is consulted by the window resizing functions. This parameter will not prevent resizing the window when the window shows another buffer than the one when @code{window-preserve-size} was invoked or if its size has changed since then. The following function can be used to check whether the height of a particular window is preserved: @defun window-preserved-size &optional window horizontal This function returns the preserved height of window @var{window} in pixels. @var{window} must be a live window and defaults to the selected one. If the optional argument @var{horizontal} is non-@code{nil}, it returns the preserved width of @var{window}. It returns @code{nil} if the size of @var{window} is not preserved. @end defun @node Splitting Windows @section Splitting Windows @cindex splitting windows @cindex window splitting This section describes functions for creating a new window by @dfn{splitting} an existing one. Note that some windows are special in the sense that these functions may fail to split them as described here. Examples of such windows are side windows (@pxref{Side Windows}) and atomic windows (@pxref{Atomic Windows}). @defun split-window &optional window size side pixelwise This function creates a new live window next to the window @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. That window is split, and reduced in size. The space is taken up by the new window, which is returned. The optional second argument @var{size} determines the sizes of @var{window} and/or the new window. If it is omitted or @code{nil}, both windows are given equal sizes; if there is an odd line, it is allocated to the new window. If @var{size} is a positive number, @var{window} is given @var{size} lines (or columns, depending on the value of @var{side}). If @var{size} is a negative number, the new window is given @minus{}@var{size} lines (or columns). If @var{size} is @code{nil}, this function obeys the variables @code{window-min-height} and @code{window-min-width} (@pxref{Window Sizes}). Thus, it signals an error if splitting would result in making a window smaller than those variables specify. However, a non-@code{nil} value for @var{size} causes those variables to be ignored; in that case, the smallest allowable window is considered to be one that has space for a text area one line tall and/or two columns wide. Hence, if @var{size} is specified, it's the caller's responsibility to check whether the emanating windows are large enough to encompass all areas like a mode line or a scroll bar. The function @code{window-min-size} (@pxref{Window Sizes}) can be used to determine the minimum requirements of @var{window} in this regard. Since the new window usually inherits areas like the mode line or the scroll bar from @var{window}, that function is also a good guess for the minimum size of the new window. The caller should specify a smaller size only if it correspondingly removes an inherited area before the next redisplay. The optional third argument @var{side} determines the position of the new window relative to @var{window}. If it is @code{nil} or @code{below}, the new window is placed below @var{window}. If it is @code{above}, the new window is placed above @var{window}. In both these cases, @var{size} specifies a total window height, in lines. If @var{side} is @code{t} or @code{right}, the new window is placed on the right of @var{window}. If @var{side} is @code{left}, the new window is placed on the left of @var{window}. In both these cases, @var{size} specifies a total window width, in columns. The optional fourth argument @var{pixelwise}, if non-@code{nil}, means to interpret @var{size} in units of pixels, instead of lines and columns. If @var{window} is a live window, the new window inherits various properties from it, including margins and scroll bars. If @var{window} is an internal window, the new window inherits the properties of the window selected within @var{window}'s frame. The behavior of this function may be altered by the window parameters of @var{window}, so long as the variable @code{ignore-window-parameters} is @code{nil}. If the value of the @code{split-window} window parameter is @code{t}, this function ignores all other window parameters. Otherwise, if the value of the @code{split-window} window parameter is a function, that function is called with the arguments @var{window}, @var{size}, and @var{side}, in lieu of the usual action of @code{split-window}. Otherwise, this function obeys the @code{window-atom} or @code{window-side} window parameter, if any. @xref{Window Parameters}. @end defun As an example, here is a sequence of @code{split-window} calls that yields the window configuration discussed in @ref{Windows and Frames}. This example demonstrates splitting a live window as well as splitting an internal window. We begin with a frame containing a single window (a live root window), which we denote by @var{W4}. Calling @code{(split-window W4)} yields this window configuration: @smallexample @group ______________________________________ | ____________________________________ | || || || || || || ||_________________W4_________________|| | ____________________________________ | || || || || || || ||_________________W5_________________|| |__________________W3__________________| @end group @end smallexample @noindent The @code{split-window} call has created a new live window, denoted by @var{W5}. It has also created a new internal window, denoted by @var{W3}, which becomes the root window and the parent of both @var{W4} and @var{W5}. Next, we call @code{(split-window W3 nil 'left)}, passing the internal window @var{W3} as the argument. The result: @smallexample @group ______________________________________ | ______ ____________________________ | || || __________________________ || || ||| ||| || ||| ||| || ||| ||| || |||____________W4____________||| || || __________________________ || || ||| ||| || ||| ||| || |||____________W5____________||| ||__W2__||_____________W3_____________ | |__________________W1__________________| @end group @end smallexample @noindent A new live window @var{W2} is created, to the left of the internal window @var{W3}. A new internal window @var{W1} is created, becoming the new root window. For interactive use, Emacs provides two commands which always split the selected window. These call @code{split-window} internally. @deffn Command split-window-right &optional size This function splits the selected window into two side-by-side windows, putting the selected window on the left. If @var{size} is positive, the left window gets @var{size} columns; if @var{size} is negative, the right window gets @minus{}@var{size} columns. @end deffn @deffn Command split-window-below &optional size This function splits the selected window into two windows, one above the other, leaving the upper window selected. If @var{size} is positive, the upper window gets @var{size} lines; if @var{size} is negative, the lower window gets @minus{}@var{size} lines. @end deffn @defopt split-window-keep-point If the value of this variable is non-@code{nil} (the default), @code{split-window-below} behaves as described above. If it is @code{nil}, @code{split-window-below} adjusts point in each of the two windows to minimize redisplay. (This is useful on slow terminals.) It selects whichever window contains the screen line that point was previously on. Note that this only affects @code{split-window-below}, not the lower-level @code{split-window} function. @end defopt @node Deleting Windows @section Deleting Windows @cindex deleting windows @dfn{Deleting} a window removes it from the frame's window tree. If the window is a live window, it disappears from the screen. If the window is an internal window, its child windows are deleted too. Even after a window is deleted, it continues to exist as a Lisp object, until there are no more references to it. Window deletion can be reversed, by restoring a saved window configuration (@pxref{Window Configurations}). @deffn Command delete-window &optional window This function removes @var{window} from display and returns @code{nil}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. If deleting the window would leave no more windows in the window tree (e.g., if it is the only live window in the frame) or all remaining windows on @var{window}'s frame are side windows (@pxref{Side Windows}), an error is signaled. If @var{window} is part of an atomic window (@pxref{Atomic Windows}), this function tries to delete the root of that atomic window instead. By default, the space taken up by @var{window} is given to one of its adjacent sibling windows, if any. However, if the variable @code{window-combination-resize} is non-@code{nil}, the space is proportionally distributed among any remaining windows in the same window combination. @xref{Recombining Windows}. The behavior of this function may be altered by the window parameters of @var{window}, so long as the variable @code{ignore-window-parameters} is @code{nil}. If the value of the @code{delete-window} window parameter is @code{t}, this function ignores all other window parameters. Otherwise, if the value of the @code{delete-window} window parameter is a function, that function is called with the argument @var{window}, in lieu of the usual action of @code{delete-window}. @xref{Window Parameters}. @end deffn @deffn Command delete-other-windows &optional window This function makes @var{window} fill its frame, deleting other windows as necessary. If @var{window} is omitted or @code{nil}, it defaults to the selected window. An error is signaled if @var{window} is a side window (@pxref{Side Windows}). If @var{window} is part of an atomic window (@pxref{Atomic Windows}), this function tries to make the root of that atomic window fill its frame. The return value is @code{nil}. The behavior of this function may be altered by the window parameters of @var{window}, so long as the variable @code{ignore-window-parameters} is @code{nil}. If the value of the @code{delete-other-windows} window parameter is @code{t}, this function ignores all other window parameters. Otherwise, if the value of the @code{delete-other-windows} window parameter is a function, that function is called with the argument @var{window}, in lieu of the usual action of @code{delete-other-windows}. @xref{Window Parameters}. Also, if @code{ignore-window-parameters} is @code{nil}, this function does not delete any window whose @code{no-delete-other-windows} parameter is non-@code{nil}. @end deffn @deffn Command delete-windows-on &optional buffer-or-name frame This function deletes all windows showing @var{buffer-or-name}, by calling @code{delete-window} on those windows. @var{buffer-or-name} should be a buffer, or the name of a buffer; if omitted or @code{nil}, it defaults to the current buffer. If there are no windows showing the specified buffer, this function does nothing. If the specified buffer is a minibuffer, an error is signaled. If there is a dedicated window showing the buffer, and that window is the only one on its frame, this function also deletes that frame if it is not the only frame on the terminal. The optional argument @var{frame} specifies which frames to operate on: @itemize @bullet @item @code{nil} means operate on all frames. @item @code{t} means operate on the selected frame. @item @code{visible} means operate on all visible frames. @item @code{0} means operate on all visible or iconified frames. @item A frame means operate on that frame. @end itemize Note that this argument does not have the same meaning as in other functions which scan all live windows (@pxref{Cyclic Window Ordering}). Specifically, the meanings of @code{t} and @code{nil} here are the opposite of what they are in those other functions. @end deffn @node Recombining Windows @section Recombining Windows @cindex recombining windows @cindex windows, recombining When deleting the last sibling of a window @var{W}, its parent window is deleted too, with @var{W} replacing it in the window tree. This means that @var{W} must be recombined with its parent's siblings to form a new window combination (@pxref{Windows and Frames}). In some occasions, deleting a live window may even entail the deletion of two internal windows. @smallexample @group ______________________________________ | ______ ____________________________ | || || __________________________ || || ||| ___________ ___________ ||| || |||| || |||| || ||||____W6_____||_____W7____|||| || |||____________W4____________||| || || __________________________ || || ||| ||| || ||| ||| || |||____________W5____________||| ||__W2__||_____________W3_____________ | |__________________W1__________________| @end group @end smallexample @noindent Deleting @var{W5} in this configuration normally causes the deletion of @var{W3} and @var{W4}. The remaining live windows @var{W2}, @var{W6} and @var{W7} are recombined to form a new horizontal combination with parent @var{W1}. Sometimes, however, it makes sense to not delete a parent window like @var{W4}. In particular, a parent window should not be removed when it was used to preserve a combination embedded in a combination of the same type. Such embeddings make sense to assure that when you split a window and subsequently delete the new window, Emacs reestablishes the layout of the associated frame as it existed before the splitting. Consider a scenario starting with two live windows @var{W2} and @var{W3} and their parent @var{W1}. @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || || || || || ||_________________W2_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent Split @var{W2} to make a new window @var{W4} as follows. @smallexample @group ______________________________________ | ____________________________________ | || || || || ||_________________W2_________________|| | ____________________________________ | || || || || ||_________________W4_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent Now, when enlarging a window vertically, Emacs tries to obtain the corresponding space from its lower sibling, provided such a window exists. In our scenario, enlarging @var{W4} will steal space from @var{W3}. @smallexample @group ______________________________________ | ____________________________________ | || || || || ||_________________W2_________________|| | ____________________________________ | || || || || || || || || ||_________________W4_________________|| | ____________________________________ | ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent Deleting @var{W4} will now give its entire space to @var{W2}, including the space earlier stolen from @var{W3}. @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || || || || || || || || || ||_________________W2_________________|| | ____________________________________ | ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent This can be counterintuitive, in particular if @var{W4} were used for displaying a buffer only temporarily (@pxref{Temporary Displays}), and you want to continue working with the initial layout. The behavior can be fixed by making a new parent window when splitting @var{W2}. The variable described next allows that to be done. @defopt window-combination-limit This variable controls whether splitting a window shall make a new parent window. The following values are recognized: @table @code @item nil This means that the new live window is allowed to share the existing parent window, if one exists, provided the split occurs in the same direction as the existing window combination (otherwise, a new internal window is created anyway). @item window-size This means that @code{display-buffer} makes a new parent window when it splits a window and is passed a @code{window-height} or @code{window-width} entry in the @var{alist} argument (@pxref{Buffer Display Action Functions}). Otherwise, window splitting behaves as for a value of @code{nil}. @item temp-buffer-resize In this case @code{with-temp-buffer-window} makes a new parent window when it splits a window and @code{temp-buffer-resize-mode} is enabled (@pxref{Temporary Displays}). Otherwise, window splitting behaves as for @code{nil}. @item temp-buffer In this case @code{with-temp-buffer-window} always makes a new parent window when it splits an existing window (@pxref{Temporary Displays}). Otherwise, window splitting behaves as for @code{nil}. @item display-buffer This means that when @code{display-buffer} (@pxref{Choosing Window}) splits a window it always makes a new parent window. Otherwise, window splitting behaves as for @code{nil}. @item t This means that splitting a window always creates a new parent window. Thus, if the value of this variable is at all times @code{t}, then at all times every window tree is a binary tree (a tree where each window except the root window has exactly one sibling). @end table The default is @code{window-size}. Other values are reserved for future use. If, as a consequence of this variable's setting, @code{split-window} makes a new parent window, it also calls @code{set-window-combination-limit} (see below) on the newly-created internal window. This affects how the window tree is rearranged when the child windows are deleted (see below). @end defopt If @code{window-combination-limit} is @code{t}, splitting @var{W2} in the initial configuration of our scenario would have produced this: @smallexample @group ______________________________________ | ____________________________________ | || __________________________________ || ||| ||| |||________________W2________________||| || __________________________________ || ||| ||| |||________________W4________________||| ||_________________W5_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent A new internal window @var{W5} has been created; its children are @var{W2} and the new live window @var{W4}. Now, @var{W2} is the only sibling of @var{W4}, so enlarging @var{W4} will try to shrink @var{W2}, leaving @var{W3} unaffected. Observe that @var{W5} represents a vertical combination of two windows embedded in the vertical combination @var{W1}. @cindex window combination limit @defun set-window-combination-limit window limit This function sets the @dfn{combination limit} of the window @var{window} to @var{limit}. This value can be retrieved via the function @code{window-combination-limit}. See below for its effects; note that it is only meaningful for internal windows. The @code{split-window} function automatically calls this function, passing it @code{t} as @var{limit}, provided the value of the variable @code{window-combination-limit} is @code{t} when it is called. @end defun @defun window-combination-limit window This function returns the combination limit for @var{window}. The combination limit is meaningful only for an internal window. If it is @code{nil}, then Emacs is allowed to automatically delete @var{window}, in response to a window deletion, in order to group the child windows of @var{window} with its sibling windows to form a new window combination. If the combination limit is @code{t}, the child windows of @var{window} are never automatically recombined with its siblings. If, in the configuration shown at the beginning of this section, the combination limit of @var{W4} (the parent window of @var{W6} and @var{W7}) is @code{t}, deleting @var{W5} will not implicitly delete @var{W4} too. @end defun Alternatively, the problems sketched above can be avoided by always resizing all windows in the same combination whenever one of its windows is split or deleted. This also permits splitting windows that would be otherwise too small for such an operation. @defopt window-combination-resize If this variable is @code{nil}, @code{split-window} can only split a window (denoted by @var{window}) if @var{window}'s screen area is large enough to accommodate both itself and the new window. If this variable is @code{t}, @code{split-window} tries to resize all windows that are part of the same combination as @var{window}, in order to accommodate the new window. In particular, this may allow @code{split-window} to succeed even if @var{window} is a fixed-size window or too small to ordinarily split. Furthermore, subsequently resizing or deleting @var{window} may resize all other windows in its combination. The default is @code{nil}. Other values are reserved for future use. A specific split operation may ignore the value of this variable if it is affected by a non-@code{nil} value of @code{window-combination-limit}. @end defopt To illustrate the effect of @code{window-combination-resize}, consider the following frame layout. @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || ||_________________W2_________________|| | ____________________________________ | || || || || || || || || ||_________________W3_________________|| |__________________W1__________________| @end group @end smallexample @noindent If @code{window-combination-resize} is @code{nil}, splitting window @var{W3} leaves the size of @var{W2} unchanged: @smallexample @group ______________________________________ | ____________________________________ | || || || || || || || || ||_________________W2_________________|| | ____________________________________ | || || ||_________________W3_________________|| | ____________________________________ | || || ||_________________W4_________________|| |__________________W1__________________| @end group @end smallexample @noindent If @code{window-combination-resize} is @code{t}, splitting @var{W3} instead leaves all three live windows with approximately the same height: @smallexample @group ______________________________________ | ____________________________________ | || || || || ||_________________W2_________________|| | ____________________________________ | || || || || ||_________________W3_________________|| | ____________________________________ | || || || || ||_________________W4_________________|| |__________________W1__________________| @end group @end smallexample @noindent Deleting any of the live windows @var{W2}, @var{W3} or @var{W4} will distribute its space proportionally among the two remaining live windows. @node Selecting Windows @section Selecting Windows @cindex selecting a window @defun select-window window &optional norecord This function makes @var{window} the selected window and the window selected within its frame (@pxref{Basic Windows}), and selects that frame. It also makes @var{window}'s buffer (@pxref{Buffers and Windows}) current and sets that buffer's value of @code{point} to the value of @code{window-point} (@pxref{Window Point}) in @var{window}. @var{window} must be a live window. The return value is @var{window}. By default, this function also moves @var{window}'s buffer to the front of the buffer list (@pxref{Buffer List}) and makes @var{window} the most recently selected window. If the optional argument @var{norecord} is non-@code{nil}, these additional actions are omitted. In addition, this function by default also tells the display engine to update the display of @var{window} when its frame gets redisplayed the next time. If @var{norecord} is non-@code{nil}, such updates are usually not performed. If, however, @var{norecord} equals the special symbol @code{mark-for-redisplay}, the additional actions mentioned above are omitted but @var{window} will be nevertheless updated. Note that sometimes selecting a window is not enough to show it, or make its frame the top-most frame on display: you may also need to raise the frame or make sure input focus is directed to that frame. @xref{Input Focus}. @end defun @cindex select window hooks @cindex running a hook when a window gets selected For historical reasons, Emacs does not run a separate hook whenever a window gets selected. Applications and internal routines often temporarily select a window to perform a few actions on it. They do that either to simplify coding---because many functions by default operate on the selected window when no @var{window} argument is specified---or because some functions did not (and still do not) take a window as argument and always operate(d) on the selected window instead. Running a hook every time a window gets selected for a short time and once more when the previously selected window gets restored is not useful. However, when its @var{norecord} argument is @code{nil}, @code{select-window} updates the buffer list and thus indirectly runs the normal hook @code{buffer-list-update-hook} (@pxref{Buffer List}). Consequently, that hook provides one way to run a function whenever a window gets selected more ``permanently''. Since @code{buffer-list-update-hook} is also run by functions that are not related to window management, it will usually make sense to save the value of the selected window somewhere and compare it with the value of @code{selected-window} while running that hook. Also, to avoid false positives when using @code{buffer-list-update-hook}, it is good practice that every @code{select-window} call supposed to select a window only temporarily passes a non-@code{nil} @var{norecord} argument. If possible, the macro @code{with-selected-window} (see below) should be used in such cases. Emacs also runs the hook @code{window-selection-change-functions} whenever the redisplay routine detects that another window has been selected since last redisplay. @xref{Window Hooks}, for a detailed explanation. @code{window-state-change-functions} (described in the same section) is another abnormal hook run after a different window has been selected but is triggered by other window changes as well. @cindex most recently selected windows The sequence of calls to @code{select-window} with a non-@code{nil} @var{norecord} argument determines an ordering of windows by their selection time. The function @code{get-lru-window} can be used to retrieve the least recently selected live window (@pxref{Cyclic Window Ordering}). @defmac save-selected-window forms@dots{} This macro records the selected frame, as well as the selected window of each frame, executes @var{forms} in sequence, then restores the earlier selected frame and windows. It also saves and restores the current buffer. It returns the value of the last form in @var{forms}. This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if @var{forms} change them, the change persists. If the previously selected window of some frame is no longer live at the time of exit from @var{forms}, that frame's selected window is left alone. If the previously selected window is no longer live, then whatever window is selected at the end of @var{forms} remains selected. The current buffer is restored if and only if it is still live when exiting @var{forms}. This macro changes neither the ordering of recently selected windows nor the buffer list. @end defmac @defmac with-selected-window window forms@dots{} This macro selects @var{window}, executes @var{forms} in sequence, then restores the previously selected window and current buffer. The ordering of recently selected windows and the buffer list remain unchanged unless you deliberately change them within @var{forms}; for example, by calling @code{select-window} with argument @var{norecord} @code{nil}. Hence, this macro is the preferred way to temporarily work with @var{window} as the selected window without needlessly running @code{buffer-list-update-hook}. @end defmac @defun frame-selected-window &optional frame This function returns the window on @var{frame} that is selected within that frame. @var{frame} should be a live frame; if omitted or @code{nil}, it defaults to the selected frame. @end defun @defun set-frame-selected-window frame window &optional norecord This function makes @var{window} the window selected within the frame @var{frame}. @var{frame} should be a live frame; if @code{nil}, it defaults to the selected frame. @var{window} should be a live window; if @code{nil}, it defaults to the selected window. If @var{frame} is the selected frame, this makes @var{window} the selected window. If the optional argument @var{norecord} is non-@code{nil}, this function does not alter the list of most recently selected windows, nor the buffer list. @end defun @cindex window use time @cindex use time of window @cindex window order by time of last use @defun window-use-time &optional window This functions returns the use time of window @var{window}. @var{window} must be a live window and defaults to the selected one. The @dfn{use time} of a window is not really a time value, but an integer that does increase monotonically with each call of @code{select-window} with a @code{nil} @var{norecord} argument. The window with the lowest use time is usually called the least recently used window while the window with the highest use time is called the most recently used one (@pxref{Cyclic Window Ordering}). @end defun @node Cyclic Window Ordering @section Cyclic Ordering of Windows @cindex cyclic ordering of windows @cindex ordering of windows, cyclic @cindex window ordering, cyclic When you use the command @w{@kbd{C-x o}} (@code{other-window}) to select some other window, it moves through live windows in a specific order. For any given configuration of windows, this order never varies. It is called the @dfn{cyclic ordering of windows}. The ordering is determined by a depth-first traversal of each frame's window tree, retrieving the live windows which are the leaf nodes of the tree (@pxref{Windows and Frames}). If the minibuffer is active, the minibuffer window is included too. The ordering is cyclic, so the last window in the sequence is followed by the first one. @defun next-window &optional window minibuf all-frames @cindex minibuffer window, and @code{next-window} This function returns a live window, the one following @var{window} in the cyclic ordering of windows. @var{window} should be a live window; if omitted or @code{nil}, it defaults to the selected window. The optional argument @var{minibuf} specifies whether minibuffer windows should be included in the cyclic ordering. Normally, when @var{minibuf} is @code{nil}, a minibuffer window is included only if it is currently active; this matches the behavior of @w{@kbd{C-x o}}. (Note that a minibuffer window is active as long as its minibuffer is in use; see @ref{Minibuffers}). If @var{minibuf} is @code{t}, the cyclic ordering includes all minibuffer windows. If @var{minibuf} is neither @code{t} nor @code{nil}, minibuffer windows are not included even if they are active. The optional argument @var{all-frames} specifies which frames to consider: @itemize @bullet @item @code{nil} means to consider windows on @var{window}'s frame. If the minibuffer window is considered (as specified by the @var{minibuf} argument), then frames that share the minibuffer window are considered too. @item @code{t} means to consider windows on all existing frames. @item @code{visible} means to consider windows on all visible frames. @item 0 means to consider windows on all visible or iconified frames. @item A frame means to consider windows on that specific frame. @item Anything else means to consider windows on @var{window}'s frame, and no others. @end itemize If more than one frame is considered, the cyclic ordering is obtained by appending the orderings for those frames, in the same order as the list of all live frames (@pxref{Finding All Frames}). @end defun @defun previous-window &optional window minibuf all-frames This function returns a live window, the one preceding @var{window} in the cyclic ordering of windows. The other arguments are handled like in @code{next-window}. @end defun @deffn Command other-window count &optional all-frames This function selects a live window, one @var{count} places from the selected window in the cyclic ordering of windows. If @var{count} is a positive number, it skips @var{count} windows forwards; if @var{count} is negative, it skips @minus{}@var{count} windows backwards; if @var{count} is zero, that simply re-selects the selected window. When called interactively, @var{count} is the numeric prefix argument. The optional argument @var{all-frames} has the same meaning as in @code{next-window}, like a @code{nil} @var{minibuf} argument to @code{next-window}. This function does not select a window that has a non-@code{nil} @code{no-other-window} window parameter (@pxref{Window Parameters}), provided that @code{ignore-window-parameters} is @code{nil}. If the @code{other-window} parameter of the selected window is a function, and @code{ignore-window-parameters} is @code{nil}, that function will be called with the arguments @var{count} and @var{all-frames} instead of the normal operation of this function. @end deffn @defun walk-windows fun &optional minibuf all-frames This function calls the function @var{fun} once for each live window, with the window as the argument. It follows the cyclic ordering of windows. The optional arguments @var{minibuf} and @var{all-frames} specify the set of windows included; these have the same arguments as in @code{next-window}. If @var{all-frames} specifies a frame, the first window walked is the first window on that frame (the one returned by @code{frame-first-window}), not necessarily the selected window. If @var{fun} changes the window configuration by splitting or deleting windows, that does not alter the set of windows walked, which is determined prior to calling @var{fun} for the first time. @end defun @defun one-window-p &optional no-mini all-frames This function returns @code{t} if the selected window is the only live window, and @code{nil} otherwise. If the minibuffer window is active, it is normally considered (so that this function returns @code{nil}). However, if the optional argument @var{no-mini} is non-@code{nil}, the minibuffer window is ignored even if active. The optional argument @var{all-frames} has the same meaning as for @code{next-window}. @end defun @cindex finding windows The following functions return a window which satisfies some criterion, without selecting it: @cindex least recently used window @defun get-lru-window &optional all-frames dedicated not-selected This function returns a live window which is heuristically the least recently used. The optional argument @var{all-frames} has the same meaning as in @code{next-window}. If any full-width windows are present, only those windows are considered. A minibuffer window is never a candidate. A dedicated window (@pxref{Dedicated Windows}) is never a candidate unless the optional argument @var{dedicated} is non-@code{nil}. The selected window is never returned, unless it is the only candidate. However, if the optional argument @var{not-selected} is non-@code{nil}, this function returns @code{nil} in that case. @end defun @cindex most recently used window @defun get-mru-window &optional all-frames dedicated not-selected This function is like @code{get-lru-window}, but it returns the most recently used window instead. The meaning of the arguments is the same as described for @code{get-lru-window}. @end defun @cindex largest window @defun get-largest-window &optional all-frames dedicated not-selected This function returns the window with the largest area (height times width). The optional argument @var{all-frames} specifies the windows to search, and has the same meaning as in @code{next-window}. A minibuffer window is never a candidate. A dedicated window (@pxref{Dedicated Windows}) is never a candidate unless the optional argument @var{dedicated} is non-@code{nil}. The selected window is not a candidate if the optional argument @var{not-selected} is non-@code{nil}. If the optional argument @var{not-selected} is non-@code{nil} and the selected window is the only candidate, this function returns @code{nil}. If there are two candidate windows of the same size, this function prefers the one that comes first in the cyclic ordering of windows, starting from the selected window. @end defun @cindex window that satisfies a predicate @cindex conditional selection of windows @defun get-window-with-predicate predicate &optional minibuf all-frames default This function calls the function @var{predicate} for each of the windows in the cyclic order of windows in turn, passing it the window as an argument. If the predicate returns non-@code{nil} for any window, this function stops and returns that window. If no such window is found, the return value is @var{default} (which defaults to @code{nil}). The optional arguments @var{minibuf} and @var{all-frames} specify the windows to search, and have the same meanings as in @code{next-window}. @end defun @node Buffers and Windows @section Buffers and Windows @cindex examining windows @cindex windows, controlling precisely @cindex buffers, controlled in windows This section describes low-level functions for examining and setting the contents of windows. @xref{Switching Buffers}, for higher-level functions for displaying a specific buffer in a window. @defun window-buffer &optional window This function returns the buffer that @var{window} is displaying. If @var{window} is omitted or @code{nil} it defaults to the selected window. If @var{window} is an internal window, this function returns @code{nil}. @end defun @defun set-window-buffer window buffer-or-name &optional keep-margins This function makes @var{window} display @var{buffer-or-name}. @var{window} should be a live window; if @code{nil}, it defaults to the selected window. @var{buffer-or-name} should be a buffer, or the name of an existing buffer. This function does not change which window is selected, nor does it directly change which buffer is current (@pxref{Current Buffer}). Its return value is @code{nil}. If @var{window} is @dfn{strongly dedicated} to a buffer and @var{buffer-or-name} does not specify that buffer, this function signals an error. @xref{Dedicated Windows}. By default, this function resets @var{window}'s position, display margins, fringe widths, and scroll bar settings, based on the local variables in the specified buffer. However, if the optional argument @var{keep-margins} is non-@code{nil}, it leaves @var{window}'s display margins, fringes and scroll bar settings alone. When writing an application, you should normally use @code{display-buffer} (@pxref{Choosing Window}) or the higher-level functions described in @ref{Switching Buffers}, instead of calling @code{set-window-buffer} directly. This runs @code{window-scroll-functions}, followed by @code{window-configuration-change-hook}. @xref{Window Hooks}. @end defun @defvar buffer-display-count This buffer-local variable records the number of times a buffer has been displayed in a window. It is incremented each time @code{set-window-buffer} is called for the buffer. @end defvar @defvar buffer-display-time This buffer-local variable records the time at which a buffer was last displayed in a window. The value is @code{nil} if the buffer has never been displayed. It is updated each time @code{set-window-buffer} is called for the buffer, with the value returned by @code{current-time} (@pxref{Time of Day}). @end defvar @defun get-buffer-window &optional buffer-or-name all-frames This function returns the first window displaying @var{buffer-or-name} in the cyclic ordering of windows, starting from the selected window (@pxref{Cyclic Window Ordering}). If no such window exists, the return value is @code{nil}. @var{buffer-or-name} should be a buffer or the name of a buffer; if omitted or @code{nil}, it defaults to the current buffer. The optional argument @var{all-frames} specifies which windows to consider: @itemize @bullet @item @code{t} means consider windows on all existing frames. @item @code{visible} means consider windows on all visible frames. @item 0 means consider windows on all visible or iconified frames. @item A frame means consider windows on that frame only. @item Any other value means consider windows on the selected frame. @end itemize Note that these meanings differ slightly from those of the @var{all-frames} argument to @code{next-window} (@pxref{Cyclic Window Ordering}). This function may be changed in a future version of Emacs to eliminate this discrepancy. @end defun @defun get-buffer-window-list &optional buffer-or-name minibuf all-frames This function returns a list of all windows currently displaying @var{buffer-or-name}. @var{buffer-or-name} should be a buffer or the name of an existing buffer. If omitted or @code{nil}, it defaults to the current buffer. If the currently selected window displays @var{buffer-or-name}, it will be the first in the list returned by this function. The arguments @var{minibuf} and @var{all-frames} have the same meanings as in the function @code{next-window} (@pxref{Cyclic Window Ordering}). Note that the @var{all-frames} argument does @emph{not} behave exactly like in @code{get-buffer-window}. @end defun @deffn Command replace-buffer-in-windows &optional buffer-or-name This command replaces @var{buffer-or-name} with some other buffer, in all windows displaying it. @var{buffer-or-name} should be a buffer, or the name of an existing buffer; if omitted or @code{nil}, it defaults to the current buffer. The replacement buffer in each window is chosen via @code{switch-to-prev-buffer} (@pxref{Window History}). Any dedicated window displaying @var{buffer-or-name} is deleted if possible (@pxref{Dedicated Windows}). If such a window is the only window on its frame and there are other frames on the same terminal, the frame is deleted as well. If the dedicated window is the only window on the only frame on its terminal, the buffer is replaced anyway. @end deffn @node Switching Buffers @section Switching to a Buffer in a Window @cindex switching to a buffer This section describes high-level functions for switching to a specified buffer in some window. In general, ``switching to a buffer'' means to (1) show the buffer in some window, (2) make that window the selected window (and its frame the selected frame), and (3) make the buffer the current buffer. Do @emph{not} use these functions to make a buffer temporarily current just so a Lisp program can access or modify it. They have side-effects, such as changing window histories (@pxref{Window History}), which will surprise the user if used that way. If you want to make a buffer current to modify it in Lisp, use @code{with-current-buffer}, @code{save-current-buffer}, or @code{set-buffer}. @xref{Current Buffer}. @deffn Command switch-to-buffer buffer-or-name &optional norecord force-same-window This command attempts to display @var{buffer-or-name} in the selected window and make it the current buffer. It is often used interactively (as the binding of @kbd{C-x b}), as well as in Lisp programs. The return value is the buffer switched to. If @var{buffer-or-name} is @code{nil}, it defaults to the buffer returned by @code{other-buffer} (@pxref{Buffer List}). If @var{buffer-or-name} is a string that is not the name of any existing buffer, this function creates a new buffer with that name; the new buffer's major mode is determined by the variable @code{major-mode} (@pxref{Major Modes}). Normally, the specified buffer is put at the front of the buffer list---both the global buffer list and the selected frame's buffer list (@pxref{Buffer List}). However, this is not done if the optional argument @var{norecord} is non-@code{nil}. Sometimes, the selected window may not be suitable for displaying the buffer. This happens if the selected window is a minibuffer window, or if the selected window is strongly dedicated to its buffer (@pxref{Dedicated Windows}). In such cases, the command normally tries to display the buffer in some other window, by invoking @code{pop-to-buffer} (see below). If the optional argument @var{force-same-window} is non-@code{nil} and the selected window is not suitable for displaying the buffer, this function always signals an error when called non-interactively. In interactive use, if the selected window is a minibuffer window, this function will try to use some other window instead. If the selected window is strongly dedicated to its buffer, the option @code{switch-to-buffer-in-dedicated-window} described next can be used to proceed. @end deffn @defopt switch-to-buffer-in-dedicated-window This option, if non-@code{nil}, allows @code{switch-to-buffer} to proceed when called interactively and the selected window is strongly dedicated to its buffer. The following values are respected: @table @code @item nil Disallows switching and signals an error as in non-interactive use. @item prompt Prompts the user whether to allow switching. @item pop Invokes @code{pop-to-buffer} to proceed. @item t Marks the selected window as non-dedicated and proceeds. @end table This option does not affect non-interactive calls of @code{switch-to-buffer}. @end defopt By default, @code{switch-to-buffer} tries to preserve @code{window-point}. This behavior can be tuned using the following option. @defopt switch-to-buffer-preserve-window-point If this variable is @code{nil}, @code{switch-to-buffer} displays the buffer specified by @var{buffer-or-name} at the position of that buffer's @code{point}. If this variable is @code{already-displayed}, it tries to display the buffer at its previous position in the selected window, provided the buffer is currently displayed in some other window on any visible or iconified frame. If this variable is @code{t}, @code{switch-to-buffer} unconditionally tries to display the buffer at its previous position in the selected window. This variable is ignored if the buffer is already displayed in the selected window or never appeared in it before, or if @code{switch-to-buffer} calls @code{pop-to-buffer} to display the buffer. @end defopt @defopt switch-to-buffer-obey-display-actions If this variable is non-@code{nil}, @code{switch-to-buffer} respects display actions specified by @code{display-buffer-overriding-action}, @code{display-buffer-alist} and other display related variables. @end defopt The next two commands are similar to @code{switch-to-buffer}, except for the described features. @deffn Command switch-to-buffer-other-window buffer-or-name &optional norecord This function displays the buffer specified by @var{buffer-or-name} in some window other than the selected window. It uses the function @code{pop-to-buffer} internally (see below). If the selected window already displays the specified buffer, it continues to do so, but another window is nonetheless found to display it as well. The @var{buffer-or-name} and @var{norecord} arguments have the same meanings as in @code{switch-to-buffer}. @end deffn @deffn Command switch-to-buffer-other-frame buffer-or-name &optional norecord This function displays the buffer specified by @var{buffer-or-name} in a new frame. It uses the function @code{pop-to-buffer} internally (see below). If the specified buffer is already displayed in another window, in any frame on the current terminal, this switches to that window instead of creating a new frame. However, the selected window is never used for this. The @var{buffer-or-name} and @var{norecord} arguments have the same meanings as in @code{switch-to-buffer}. @end deffn The above commands use the function @code{pop-to-buffer}, which flexibly displays a buffer in some window and selects that window for editing. In turn, @code{pop-to-buffer} uses @code{display-buffer} for displaying the buffer. Hence, all the variables affecting @code{display-buffer} will affect it as well. @xref{Choosing Window}, for the documentation of @code{display-buffer}. @deffn Command pop-to-buffer buffer-or-name &optional action norecord This function makes @var{buffer-or-name} the current buffer and displays it in some window, preferably not the window currently selected. It then selects the displaying window. If that window is on a different graphical frame, that frame is given input focus if possible (@pxref{Input Focus}). If @var{buffer-or-name} is @code{nil}, it defaults to the buffer returned by @code{other-buffer} (@pxref{Buffer List}). If @var{buffer-or-name} is a string that is not the name of any existing buffer, this function creates a new buffer with that name; the new buffer's major mode is determined by the variable @code{major-mode} (@pxref{Major Modes}). In any case, that buffer is made current and returned, even when no suitable window was found to display it. If @var{action} is non-@code{nil}, it should be a display action to pass to @code{display-buffer} (@pxref{Choosing Window}). Alternatively, a non-@code{nil}, non-list value means to pop to a window other than the selected one---even if the buffer is already displayed in the selected window. Like @code{switch-to-buffer}, this function updates the buffer list unless @var{norecord} is non-@code{nil}. @end deffn @node Displaying Buffers @section Displaying a Buffer in a Suitable Window @cindex buffer display @cindex displaying a buffer This section describes lower-level functions Emacs uses to find or create a window for displaying a specified buffer. The common workhorse of these functions is @code{display-buffer} which eventually handles all incoming requests for buffer display (@pxref{Choosing Window}). @code{display-buffer} delegates the task of finding a suitable window to so-called action functions (@pxref{Buffer Display Action Functions}). First, @code{display-buffer} compiles a so-called action alist---a special association list that action functions can use to fine-tune their behavior. Then it passes that alist on to each action function it calls (@pxref{Buffer Display Action Alists}). The behavior of @code{display-buffer} is highly customizable. To understand how customizations are used in practice, you may wish to study examples illustrating the order of precedence which @code{display-buffer} uses to call action functions (@pxref{Precedence of Action Functions}). To avoid conflicts between Lisp programs calling @code{display-buffer} and user customizations of its behavior, it may make sense to follow a number of guidelines which are sketched in the final part of this section (@pxref{The Zen of Buffer Display}). @menu * Choosing Window:: How to choose a window for displaying a buffer. * Buffer Display Action Functions:: Support functions for buffer display. * Buffer Display Action Alists:: Alists for fine-tuning buffer display. * Choosing Window Options:: Extra options affecting how buffers are displayed. * Precedence of Action Functions:: Examples to explain the precedence of action functions. * The Zen of Buffer Display:: How to avoid that buffers get lost in between windows. @end menu @node Choosing Window @subsection Choosing a Window for Displaying a Buffer The command @code{display-buffer} flexibly chooses a window for display, and displays a specified buffer in that window. It can be called interactively, via the key binding @kbd{C-x 4 C-o}. It is also used as a subroutine by many functions and commands, including @code{switch-to-buffer} and @code{pop-to-buffer} (@pxref{Switching Buffers}). @cindex buffer display display action @cindex display action This command performs several complex steps to find a window to display in. These steps are described by means of @dfn{display actions}, which have the form @code{(@var{functions} . @var{alist})}. Here, @var{functions} is either a single function or a list of functions, referred to as ``action functions'' (@pxref{Buffer Display Action Functions}); and @var{alist} is an association list, referred to as ``action alist'' (@pxref{Buffer Display Action Alists}). @xref{The Zen of Buffer Display}, for samples of display actions. An action function accepts two arguments: the buffer to display and an action alist. It attempts to display the buffer in some window, picking or creating a window according to its own criteria. If successful, it returns the window; otherwise, it returns @code{nil}. @code{display-buffer} works by combining display actions from several sources, and calling the action functions in turn, until one of them manages to display the buffer and returns a non-@code{nil} value. @deffn Command display-buffer buffer-or-name &optional action frame This command makes @var{buffer-or-name} appear in some window, without selecting the window or making the buffer current. The argument @var{buffer-or-name} must be a buffer or the name of an existing buffer. The return value is the window chosen to display the buffer, or @code{nil} if no suitable window was found. The optional argument @var{action}, if non-@code{nil}, should normally be a display action (described above). @code{display-buffer} builds a list of action functions and an action alist, by consolidating display actions from the following sources (in order of their precedence, from highest to lowest): @itemize @item The variable @code{display-buffer-overriding-action}. @item The user option @code{display-buffer-alist}. @item The @var{action} argument. @item The user option @code{display-buffer-base-action}. @item The constant @code{display-buffer-fallback-action}. @end itemize @noindent In practice this means that @code{display-buffer} builds a list of all action functions specified by these display actions. The first element of this list is the first action function specified by @code{display-buffer-overriding-action}, if any. Its last element is @code{display-buffer-pop-up-frame}---the last action function specified by @code{display-buffer-fallback-action}. Duplicates are not removed from this list---hence one and the same action function may be called multiple times during one call of @code{display-buffer}. @code{display-buffer} calls the action functions specified by this list in turn, passing the buffer as the first argument and the combined action alist as the second argument, until one of the functions returns non-@code{nil}. @xref{Precedence of Action Functions}, for examples how display actions specified by different sources are processed by @code{display-buffer}. Note that the second argument is always the list of @emph{all} action alist entries specified by the sources named above. Hence, the first element of that list is the first action alist entry specified by @code{display-buffer-overriding-action}, if any. Its last element is the last alist entry of @code{display-buffer-base-action}, if any (the action alist of @code{display-buffer-fallback-action} is empty). Note also, that the combined action alist may contain duplicate entries and entries for the same key with different values. As a rule, action functions always use the first association of a key they find. Hence, the association an action function uses is not necessarily the association provided by the display action that specified that action function, The argument @var{action} can also have a non-@code{nil}, non-list value. This has the special meaning that the buffer should be displayed in a window other than the selected one, even if the selected window is already displaying it. If called interactively with a prefix argument, @var{action} is @code{t}. Lisp programs should always supply a list value. The optional argument @var{frame}, if non-@code{nil}, specifies which frames to check when deciding whether the buffer is already displayed. It is equivalent to adding an element @w{@code{(reusable-frames . @var{frame})}} to the action alist of @var{action} (@pxref{Buffer Display Action Alists}). The @var{frame} argument is provided for compatibility reasons, Lisp programs should not use it. @end deffn @defvar display-buffer-overriding-action The value of this variable should be a display action, which is treated with the highest priority by @code{display-buffer}. The default value is an empty display action, i.e., @w{@code{(nil . nil)}}. @end defvar @defopt display-buffer-alist The value of this option is an alist mapping conditions to display actions. Each condition may be either a regular expression matching a buffer name or a function that takes two arguments: a buffer name and the @var{action} argument passed to @code{display-buffer}. If either the name of the buffer passed to @code{display-buffer} matches a regular expression in this alist, or the function specified by a condition returns non-@code{nil}, then @code{display-buffer} uses the corresponding display action to display the buffer. @end defopt @defopt display-buffer-base-action The value of this option should be a display action. This option can be used to define a standard display action for calls to @code{display-buffer}. @end defopt @defvr Constant display-buffer-fallback-action This display action specifies the fallback behavior for @code{display-buffer} if no other display actions are given. @end defvr @node Buffer Display Action Functions @subsection Action Functions for Buffer Display @cindex buffer display action function @cindex action function, for buffer display An @dfn{action function} is a function @code{display-buffer} calls for choosing a window to display a buffer. Action functions take two arguments: @var{buffer}, the buffer to display, and @var{alist}, an action alist (@pxref{Buffer Display Action Alists}). They are supposed to return a window displaying @var{buffer} if they succeed and @code{nil} if they fail. The following basic action functions are defined in Emacs. @defun display-buffer-same-window buffer alist This function tries to display @var{buffer} in the selected window. It fails if the selected window is a minibuffer window or is dedicated to another buffer (@pxref{Dedicated Windows}). It also fails if @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry. @end defun @defun display-buffer-reuse-window buffer alist This function tries to display @var{buffer} by finding a window that is already displaying it. Windows on the selected frame are preferred to windows on other frames. If @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry, the selected window is not eligible for reuse. The set of frames to search for a window already displaying @var{buffer} can be specified with the help of the @code{reusable-frames} action alist entry. If @var{alist} contains no @code{reusable-frames} entry, this function searches just the selected frame. If this function chooses a window on another frame, it makes that frame visible and, unless @var{alist} contains an @code{inhibit-switch-frame} entry, raises that frame if necessary. @end defun @defun display-buffer-reuse-mode-window buffer alist This function tries to display @var{buffer} by finding a window that is displaying a buffer in a given mode. If @var{alist} contains a @code{mode} entry, its value specifes a major mode (a symbol) or a list of major modes. If @var{alist} contains no @code{mode} entry, the current major mode of @var{buffer} is used instead. A window is a candidate if it displays a buffer whose mode derives from one of the modes specified thusly. The behavior is also controlled by @var{alist} entries for @code{inhibit-same-window}, @code{reusable-frames} and @code{inhibit-switch-frame}, like @code{display-buffer-reuse-window} does. @end defun @defun display-buffer-pop-up-window buffer alist This function tries to display @var{buffer} by splitting the largest or least recently-used window (usually located on the selected frame). It actually performs the split by calling the function specified by @code{split-window-preferred-function} (@pxref{Choosing Window Options}). The size of the new window can be adjusted by supplying @code{window-height} and @code{window-width} entries in @var{alist}. If @var{alist} contains a @code{preserve-size} entry, Emacs will also try to preserve the size of the new window during future resize operations (@pxref{Preserving Window Sizes}). This function fails if no window can be split. More often than not, this happens because no window is large enough to allow splitting. Setting @code{split-height-threshold} or @code{split-width-threshold} to lower values may help in this regard. Splitting also fails when the selected frame has an @code{unsplittable} frame parameter; @pxref{Buffer Parameters}. @end defun @defun display-buffer-in-previous-window buffer alist This function tries to display @var{buffer} in a window where it was displayed previously. If @var{alist} contains a non-@code{nil} @code{inhibit-same-window} entry, the selected window is not eligible for use. A dedicated window is usable only if it already shows @var{buffer}. If @var{alist} contains a @code{previous-window} entry, the window specified by that entry is usable even if it never showed @var{buffer} before. If @var{alist} contains a @code{reusable-frames} entry (@pxref{Buffer Display Action Alists}), its value determines which frames to search for a suitable window. If @var{alist} contains no @code{reusable-frames} entry, this function searches just the selected frame if @code{display-buffer-reuse-frames} and @code{pop-up-frames} are both @code{nil}; it searches all frames on the current terminal if either of those variables is non-@code{nil}. If more than one window qualifies as usable according to these rules, this function makes a choice in the following order of preference: @itemize @bullet @item The window specified by any @code{previous-window} @var{alist} entry, provided it is not the selected window. @item A window that showed @var{buffer} before, provided it is not the selected window. @item The selected window if it is either specified by a @code{previous-window} @var{alist} entry or showed @var{buffer} before. @end itemize @end defun @defun display-buffer-use-some-window buffer alist This function tries to display @var{buffer} by choosing an existing window and displaying the buffer in that window. It can fail if all windows are dedicated to other buffers (@pxref{Dedicated Windows}). @end defun @defun display-buffer-use-least-recent-window buffer alist This function is like @code{display-buffer-use-some-window}, but will not reuse the current window, and will use the least recently switched-to window. @end defun @defun display-buffer-in-direction buffer alist This function tries to display @var{buffer} at a location specified by @var{alist}. For this purpose, @var{alist} should contain a @code{direction} entry whose value is one of @code{left}, @code{above} (or @code{up}), @code{right} and @code{below} (or @code{down}). Other values are usually interpreted as @code{below}. If @var{alist} also contains a @code{window} entry, its value specifies a reference window. That value can be a special symbol like @code{main} which stands for the selected frame's main window (@pxref{Side Window Options and Functions}) or @code{root} standing for the selected frame's root window (@pxref{Windows and Frames}). It can also specify an arbitrary valid window. Any other value (or omitting the @code{window} entry entirely) means to use the selected window as reference window. This function first tries to reuse a window in the specified direction that already shows @var{buffer}. If no such window exists, it tries to split the reference window in order to produce a new window in the specified direction. If this fails as well, it will try to display @var{buffer} in an existing window in the specified direction. In either case, the window chosen will appear on the side of the reference window specified by the @code{direction} entry, sharing at least one edge with the reference window. If the reference window is live, the edge the chosen window will share with it is always the opposite of the one specified by the @code{direction} entry. For example, if the value of the @code{direction} entry is @code{left}, the chosen window's right edge coordinate (@pxref{Coordinates and Windows}) will equal the reference window's left edge coordinate. If the reference window is internal, a reused window must share with it the edge specified by the @code{direction} entry. Hence if, for example, the reference window is the frame's root window and the value of the @code{direction} entry is @code{left}, a reused window must be on the left of the frame. This means that the left edge coordinate of the chosen window and that of the reference window are the same. A new window, however, will be created by splitting the reference window such that the chosen window will share the opposite edge with the reference window. In our example, a new root window would be created with a new live window and the reference window as its children. The chosen window's right edge coordinate would then equal the left edge coordinate of the reference window. Its left edge coordinate would equal the left edge coordinate of the frame's new root window. Four special values for @code{direction} entries allow to implicitly specify the selected frame's main window as the reference window: @code{leftmost}, @code{top}, @code{rightmost} and @code{bottom}. This means that instead of, for example, @w{@code{(direction . left) (window . main)}} one can just specify @w{@code{(direction . leftmost)}}. An existing @code{window} @var{alist} entry is ignored in such cases. @end defun @defun display-buffer-below-selected buffer alist This function tries to display @var{buffer} in a window below the selected window. If there is a window below the selected one and that window already displays @var{buffer}, it reuses that window. If there is no such window, this function tries to create a new window by splitting the selected one, and displays @var{buffer} there. It will also try to adjust that window's size provided @var{alist} contains a suitable @code{window-height} or @code{window-width} entry, see above. If splitting the selected window fails and there is a non-dedicated window below the selected one showing some other buffer, this function tries to use that window for showing @var{buffer}. If @var{alist} contains a @code{window-min-height} entry, this function ensures that the window used is or can become at least as high as specified by that entry's value. Note that this is only a guarantee. In order to actually resize the window used, @var{alist} must also provide an appropriate @code{window-height} entry. @end defun @defun display-buffer-at-bottom buffer alist This function tries to display @var{buffer} in a window at the bottom of the selected frame. This either tries to split the window at the bottom of the frame or the frame's root window, or to reuse an existing window at the bottom of the selected frame. @end defun @defun display-buffer-pop-up-frame buffer alist This function creates a new frame, and displays the buffer in that frame's window. It actually performs the frame creation by calling the function specified in @code{pop-up-frame-function} (@pxref{Choosing Window Options}). If @var{alist} contains a @code{pop-up-frame-parameters} entry, the associated value is added to the newly created frame's parameters. @end defun @defun display-buffer-in-child-frame buffer alist This function tries to display @var{buffer} in a child frame (@pxref{Child Frames}) of the selected frame, either reusing an existing child frame or by making a new one. If @var{alist} has a non-@code{nil} @code{child-frame-parameters} entry, the corresponding value is an alist of frame parameters to give the new frame. A @code{parent-frame} parameter specifying the selected frame is provided by default. If the child frame should become the child of another frame, a corresponding entry must be added to @var{alist}. The appearance of child frames is largely dependent on the parameters provided via @var{alist}. It is advisable to use at least ratios to specify the size (@pxref{Size Parameters}) and the position (@pxref{Position Parameters}) of the child frame, and to add a @code{keep-ratio} parameter (@pxref{Frame Interaction Parameters}), in order to make sure that the child frame remains visible. For other parameters that should be considered see @ref{Child Frames}. @end defun @defun display-buffer-use-some-frame buffer alist This function tries to display @var{buffer} by finding a frame that meets a predicate (by default any frame other than the selected frame). If this function chooses a window on another frame, it makes that frame visible and, unless @var{alist} contains an @code{inhibit-switch-frame} entry, raises that frame if necessary. If @var{alist} has a non-@code{nil} @code{frame-predicate} entry, its value is a function taking one argument (a frame), returning non-@code{nil} if the frame is a candidate; this function replaces the default predicate. If @var{alist} has a non-@code{nil} @code{inhibit-same-window} entry, the selected window is not used; thus if the selected frame has a single window, it is not used. @end defun @defun display-buffer-no-window buffer alist If @var{alist} has a non-@code{nil} @code{allow-no-window} entry, then this function does not display @var{buffer} and returns the symbol @code{fail}. This constitutes the only exception to the convention that an action function returns either @code{nil} or a window showing @var{buffer}. If @var{alist} has no such @code{allow-no-window} entry, this function returns @code{nil}. If this function returns @code{fail}, @code{display-buffer} will skip the execution of any further display actions and return @code{nil} immediately. If this function returns @code{nil}, @code{display-buffer} will continue with the next display action, if any. It is assumed that when a caller of @code{display-buffer} specifies a non-@code{nil} @code{allow-no-window} entry, it is also able to handle a @code{nil} return value. @end defun Two other action functions are described in their proper sections---@code{display-buffer-in-side-window} (@pxref{Displaying Buffers in Side Windows}) and @code{display-buffer-in-atom-window} (@pxref{Atomic Windows}). @node Buffer Display Action Alists @subsection Action Alists for Buffer Display @cindex buffer display action alist @cindex action alist for buffer display An @dfn{action alist} is an association list mapping predefined symbols recognized by action functions to values these functions are supposed to interpret accordingly. In each call, @code{display-buffer} constructs a new, possibly empty action alist and passes that entire list on to any action function it calls. By design, action functions are free in their interpretation of action alist entries. In fact, some entries like @code{allow-no-window} or @code{previous-window} have a meaning only for one or a few action functions, and are ignored by the rest. Other entries, like @code{inhibit-same-window} or @code{window-parameters}, are supposed to be respected by most action functions, including those provided by application programs and external packages. In the previous subsection we have described in detail how individual action functions interpret the action alist entries they care about. Here we give a reference list of all known action alist entries according to their symbols, together with their values and action functions (@pxref{Buffer Display Action Functions}) that recognize them. Throughout this list, the terms ``buffer'' will refer to the buffer @code{display-buffer} is supposed to display, and ``value'' refers to the entry's value. @table @code @vindex inhibit-same-window@r{, a buffer display action alist entry} @item inhibit-same-window If the value is non-@code{nil}, this signals that the selected window must not be used for displaying the buffer. All action functions that (re-)use an existing window should respect this entry. @vindex previous-window@r{, a buffer display action alist entry} @item previous-window The value must specify a window that may have displayed the buffer previously. @code{display-buffer-in-previous-window} will give preference to such a window provided it is still live and not dedicated to another buffer. @vindex mode@r{, a buffer display action alist entry} @item mode The value is either a major mode or a list of major modes. @code{display-buffer-reuse-mode-window} may reuse a window whenever the value specified by this entry matches the major mode of that window's buffer. Other action functions ignore such entries. @vindex frame-predicate@r{, a buffer display action alist entry} @item frame-predicate The value must be a function taking one argument (a frame), supposed to return non-@code{nil} if that frame is a candidate for displaying the buffer. This entry is used by @code{display-buffer-use-some-frame}. @vindex reusable-frames@r{, a buffer display action alist entry} @item reusable-frames The value specifies the set of frames to search for a window that can be reused because it already displays the buffer. It can be set as follows: @itemize @bullet @item @code{nil} means consider only windows on the selected frame. (Actually, the last frame used that is not a minibuffer-only frame.) @item @code{t} means consider windows on all frames. @item @code{visible} means consider windows on all visible frames. @item 0 means consider windows on all visible or iconified frames. @item A frame means consider windows on that frame only. @end itemize Note that the meaning of @code{nil} differs slightly from that of the @var{all-frames} argument to @code{next-window} (@pxref{Cyclic Window Ordering}). A major client of this is @code{display-buffer-reuse-window}, but all other action functions that try to reuse a window are affected as well. @code{display-buffer-in-previous-window} consults it when searching for a window that previously displayed the buffer on another frame. @vindex inhibit-switch-frame@r{, a buffer display action alist entry} @item inhibit-switch-frame A non-@code{nil} value prevents another frame from being raised or selected, if the window chosen by @code{display-buffer} is displayed there. Primarily affected by this are @code{display-buffer-use-some-frame} and @code{display-buffer-reuse-window}. @code{display-buffer-pop-up-frame} should be affected as well, but there is no guarantee that the window manager will comply. @vindex window-parameters@r{, a buffer display action alist entry} @item window-parameters The value specifies an alist of window parameters to give the chosen window. All action functions that choose a window should process this entry. @vindex window-min-height@r{, a buffer display action alist entry} @item window-min-height The value specifies a minimum height of the window used, in lines. If a window is not or cannot be made as high as specified by this entry, the window is not considered for use. The only client of this entry is presently @code{display-buffer-below-selected}. Note that providing such an entry alone does not necessarily make the window as tall as specified by its value. To actually resize an existing window or make a new window as tall as specified by that value, a @code{window-height} entry specifying that value should be provided as well. Such a @code{window-height} entry can, however, specify a completely different value or ask the window height to be fit to that of its buffer in which case the @code{window-min-height} entry provides the guaranteed minimum height of the window used. @vindex window-height@r{, a buffer display action alist entry} @item window-height The value specifies whether and how to adjust the height of the chosen window and can be one of the following: @itemize @bullet @item @code{nil} means to leave the height of the chosen window alone. @item An integer number specifies the desired total height of the chosen window in lines. @item A floating-point number specifies the fraction of the chosen window's desired total height with respect to the total height of its frame's root window. @item If the value specifies a function, that function is called with one argument---the chosen window. The function is supposed to adjust the height of the window; its return value is ignored. Suitable functions are @code{shrink-window-if-larger-than-buffer} and @code{fit-window-to-buffer}, see @ref{Resizing Windows}. @end itemize By convention, the height of the chosen window is adjusted only if the window is part of a vertical combination (@pxref{Windows and Frames}) to avoid changing the height of other, unrelated windows. Also, this entry should be processed only under certain conditions which are specified right below this list. @vindex window-width@r{, a buffer display action alist entry} @item window-width This entry is similar to the @code{window-height} entry described before, but used to adjust the chosen window's width instead. The value can be one of the following: @itemize @bullet @item @code{nil} means to leave the width of the chosen window alone. @item An integer specifies the desired total width of the chosen window in columns. @item A floating-point number specifies the fraction of the chosen window's desired total width with respect to the total width of the frame's root window. @item If the value specifies a function, that function is called with one argument---the chosen window. The function is supposed to adjust the width of the window; its return value is ignored. @end itemize By convention, the width of the chosen window is adjusted only if the window is part of a horizontal combination (@pxref{Windows and Frames}) to avoid changing the width of other, unrelated windows. Also, this entry should be processed under only certain conditions which are specified right below this list. @vindex dedicated@r{, a buffer display action alist entry} @item dedicated If non-@code{nil}, such an entry tells @code{display-buffer} to mark any window it creates as dedicated to its buffer (@pxref{Dedicated Windows}). It does that by calling @code{set-window-dedicated-p} with the chosen window as first argument and the entry's value as second. @vindex preserve-size@r{, a buffer display action alist entry} @item preserve-size If non-@code{nil} such an entry tells Emacs to preserve the size of the window chosen (@pxref{Preserving Window Sizes}). The value should be either @w{@code{(t . nil)}} to preserve the width of the window, @w{@code{(nil . t)}} to preserve its height or @w{@code{(t . t)}} to preserve both, its width and its height. This entry should be processed only under certain conditions which are specified right after this list. @vindex pop-up-frame-parameters@r{, a buffer display action alist entry} @item pop-up-frame-parameters The value specifies an alist of frame parameters to give a new frame, if one is created. @code{display-buffer-pop-up-frame} is its one and only addressee. @vindex parent-frame@r{, a buffer display action alist entry} @item parent-frame The value specifies the parent frame to be used when the buffer is displayed on a child frame. This entry is used only by @code{display-buffer-in-child-frame}. @vindex child-frame-parameters@r{, a buffer display action alist entry} @item child-frame-parameters The value specifies an alist of frame parameters to use when the buffer is displayed on a child frame. This entry is used only by @code{display-buffer-in-child-frame}. @vindex side@r{, a buffer display action alist entry} @item side The value denotes the side of the frame or window where a new window displaying the buffer shall be created. This entry is used by @code{display-buffer-in-side-window} to indicate the side of the frame where a new side window shall be placed (@pxref{Displaying Buffers in Side Windows}). It is also used by @code{display-buffer-in-atom-window} to indicate the side of an existing window where the new window shall be located (@pxref{Atomic Windows}). @vindex slot@r{, a buffer display action alist entry} @item slot If non-@code{nil}, the value specifies the slot of the side window supposed to display the buffer. This entry is used only by @code{display-buffer-in-side-window}. @vindex direction@r{, a buffer display action alist entry} @item direction The value specifies a direction which, together with a @code{window} entry, allows @code{display-buffer-in-direction} to determine the location of the window to display the buffer. @vindex window@r{, a buffer display action alist entry} @item window The value specifies a window that is in some way related to the window chosen by @code{display-buffer}. This entry is currently used by @code{display-buffer-in-atom-window} to indicate the window on whose side the new window shall be created. It is also used by @code{display-buffer-in-direction} to specify the reference window on whose side the resulting window shall appear. @vindex allow-no-window@r{, a buffer display action alist entry} @item allow-no-window If the value is non-@code{nil}, @code{display-buffer} does not necessarily have to display the buffer and the caller is prepared to accept that. This entry is not intended for user customizations, since there is no guarantee that an arbitrary caller of @code{display-buffer} will be able to handle the case that no window will display the buffer. @code{display-buffer-no-window} is the only action function that cares about this entry. @vindex body-function@r{, a buffer display action alist entry} @item body-function The value must be a function taking one argument (a displayed window). This function can be used to fill the displayed window's body with some contents that might depend on dimensions of the displayed window. It is called @emph{after} the buffer is displayed, and @emph{before} the entries @code{window-height}, @code{window-width} and @code{preserve-size} are applied that could resize the window to fit it to the inserted contents. @end table By convention, the entries @code{window-height}, @code{window-width} and @code{preserve-size} are applied after the chosen window's buffer has been set up and if and only if that window never showed another buffer before. More precisely, the latter means that the window must have been either created by the current @code{display-buffer} call or the window was created earlier by @code{display-buffer} to show the buffer and never was used to show another buffer until it was reused by the current invocation of @code{display-buffer}. @node Choosing Window Options @subsection Additional Options for Displaying Buffers The behavior of buffer display actions (@pxref{Choosing Window}) can be further modified by the following user options. @defopt pop-up-windows If the value of this variable is non-@code{nil}, @code{display-buffer} is allowed to split an existing window to make a new window for displaying in. This is the default. This variable is provided for backward compatibility only. It is obeyed by @code{display-buffer} via a special mechanism in @code{display-buffer-fallback-action}, which calls the action function @code{display-buffer-pop-up-window} (@pxref{Buffer Display Action Functions}) when the value of this option is non-@code{nil}. It is not consulted by @code{display-buffer-pop-up-window} itself, which the user may specify directly in @code{display-buffer-alist} etc. @end defopt @defopt split-window-preferred-function This variable specifies a function for splitting a window, in order to make a new window for displaying a buffer. It is used by the @code{display-buffer-pop-up-window} action function to actually split the window. The value must be a function that takes one argument, a window, and returns either a new window (which will be used to display the desired buffer) or @code{nil} (which means the splitting failed). The default value is @code{split-window-sensibly}, which is documented next. @end defopt @defun split-window-sensibly &optional window This function tries to split @var{window} and return the newly created window. If @var{window} cannot be split, it returns @code{nil}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. This function obeys the usual rules that determine when a window may be split (@pxref{Splitting Windows}). It first tries to split by placing the new window below, subject to the restriction imposed by @code{split-height-threshold} (see below), in addition to any other restrictions. If that fails, it tries to split by placing the new window to the right, subject to @code{split-width-threshold} (see below). If that also fails, and the window is the only window on its frame, this function again tries to split and place the new window below, disregarding @code{split-height-threshold}. If this fails as well, this function gives up and returns @code{nil}. @end defun @defopt split-height-threshold This variable specifies whether @code{split-window-sensibly} is allowed to split the window placing the new window below. If it is an integer, that means to split only if the original window has at least that many lines. If it is @code{nil}, that means not to split this way. @end defopt @defopt split-width-threshold This variable specifies whether @code{split-window-sensibly} is allowed to split the window placing the new window to the right. If the value is an integer, that means to split only if the original window has at least that many columns. If the value is @code{nil}, that means not to split this way. @end defopt @defopt even-window-sizes This variable, if non-@code{nil}, causes @code{display-buffer} to even window sizes whenever it reuses an existing window, and that window is adjacent to the selected one. If its value is @code{width-only}, sizes are evened only if the reused window is on the left or right of the selected one and the selected window is wider than the reused one. If its value is @code{height-only} sizes are evened only if the reused window is above or beneath the selected window and the selected window is higher than the reused one. Any other non-@code{nil} value means to even sizes in any of these cases provided the selected window is larger than the reused one in the sense of their combination. @end defopt @defopt pop-up-frames If the value of this variable is non-@code{nil}, that means @code{display-buffer} may display buffers by making new frames. The default is @code{nil}. A non-@code{nil} value also means that when @code{display-buffer} is looking for a window already displaying @var{buffer-or-name}, it can search any visible or iconified frame, not just the selected frame. This variable is provided mainly for backward compatibility. It is obeyed by @code{display-buffer} via a special mechanism in @code{display-buffer-fallback-action}, which calls the action function @code{display-buffer-pop-up-frame} (@pxref{Buffer Display Action Functions}) if the value is non-@code{nil}. (This is done before attempting to split a window.) This variable is not consulted by @code{display-buffer-pop-up-frame} itself, which the user may specify directly in @code{display-buffer-alist} etc. @end defopt @defopt pop-up-frame-function This variable specifies a function for creating a new frame, in order to make a new window for displaying a buffer. It is used by the @code{display-buffer-pop-up-frame} action function. The value should be a function that takes no arguments and returns a frame, or @code{nil} if no frame could be created. The default value is a function that creates a frame using the parameters specified by @code{pop-up-frame-alist} (see below). @end defopt @defopt pop-up-frame-alist This variable holds an alist of frame parameters (@pxref{Frame Parameters}), which is used by the function specified by @code{pop-up-frame-function} to make a new frame. The default is @code{nil}. This option is provided for backward compatibility only. Note, that when @code{display-buffer-pop-up-frame} calls the function specified by @code{pop-up-frame-function}, it prepends the value of all @code{pop-up-frame-parameters} action alist entries to @code{pop-up-frame-alist} so that the values specified by the action alist entry effectively override any corresponding values of @code{pop-up-frame-alist}. Hence, users should set up a @code{pop-up-frame-parameters} action alist entry in @code{display-buffer-alist} instead of customizing @code{pop-up-frame-alist}. Only this will guarantee that the value of a parameter specified by the user overrides the value of that parameter specified by the caller of @code{display-buffer}. @end defopt Many efforts in the design of @code{display-buffer} have been given to maintain compatibility with code that uses older options like @code{pop-up-windows}, @code{pop-up-frames}, @code{pop-up-frame-alist}, @code{same-window-buffer-names} and @code{same-window-regexps}. Lisp Programs and users should refrain from using these options. Above we already warned against customizing @code{pop-up-frame-alist}. Here we describe how to convert the remaining options to use display actions instead. @table @code @item pop-up-windows @vindex pop-up-windows@r{, replacement for} This variable is @code{t} by default. Instead of customizing it to @code{nil} and thus telling @code{display-buffer} what not to do, it's much better to list in @code{display-buffer-base-action} the action functions it should try instead as, for example: @example @group (customize-set-variable 'display-buffer-base-action '((display-buffer-reuse-window display-buffer-same-window display-buffer-in-previous-window display-buffer-use-some-window))) @end group @end example @item pop-up-frames @vindex pop-up-frames@r{, replacement for} Instead of customizing this variable to @code{t}, customize @code{display-buffer-base-action}, for example, as follows: @example @group (customize-set-variable 'display-buffer-base-action '((display-buffer-reuse-window display-buffer-pop-up-frame) (reusable-frames . 0))) @end group @end example @item same-window-buffer-names @itemx same-window-regexps @vindex same-window-buffer-names@r{, replacement for} @vindex same-window-regexps@r{, replacement for} Instead of adding a buffer name or a regular expression to one of these options use a @code{display-buffer-alist} entry for that buffer specifying the action function @code{display-buffer-same-window}. @example @group (customize-set-variable 'display-buffer-alist (cons '("\\*foo\\*" (display-buffer-same-window)) display-buffer-alist)) @end group @end example @end table @node Precedence of Action Functions @subsection Precedence of Action Functions @cindex precedence of buffer display action functions @cindex execution order of buffer display action functions @cindex buffer display action functions, precedence From the past subsections we already know that @code{display-buffer} must be supplied with a number of display actions (@pxref{Choosing Window}) in order to display a buffer. In a completely uncustomized Emacs, these actions are specified by @code{display-buffer-fallback-action} in the following order of precedence: Reuse a window, pop up a new window on the same frame, use a window previously showing the buffer, use some window and pop up a new frame. (Note that the remaining actions named by @code{display-buffer-fallback-action} are void in an uncustomized Emacs). Consider the following form: @example (display-buffer (get-buffer-create "*foo*")) @end example @noindent Evaluating this form in the buffer @file{*scratch*} of an uncustomized Emacs session will usually fail to reuse a window that shows @file{*foo*} already, but succeed in popping up a new window. Evaluating the same form again will now not cause any visible changes---@code{display-buffer} reused the window already showing @file{*foo*} because that action was applicable and had the highest precedence among all applicable actions. Popping up a new window will fail if there is not enough space on the selected frame. In an uncustomized Emacs it typically fails when there are already two windows on a frame. For example, if you now type @w{@kbd{C-x 1}} followed by @w{@kbd{C-x 2}} and evaluate the form once more, @file{*foo*} should show up in the lower window---@code{display-buffer} just used ``some'' window. If, before typing @w{@kbd{C-x 2}} you had typed @w{@kbd{C-x o}}, @file{*foo*} would have been shown in the upper window because ``some'' window stands for the ``least recently used'' window and the selected window has been least recently used if and only if it is alone on its frame. Let's assume you did not type @w{@kbd{C-x o}} and @file{*foo*} is shown in the lower window. Type @w{@kbd{C-x o}} to get there followed by @w{@kbd{C-x left}} and evaluate the form again. This should display @file{*foo*} in the same, lower window because that window had already shown @file{*foo*} previously and was therefore chosen instead of some other window. So far we have only observed the default behavior in an uncustomized Emacs session. To see how this behavior can be customized, let's consider the option @code{display-buffer-base-action}. It provides a very coarse customization which conceptually affects the display of @emph{any} buffer. It can be used to supplement the actions supplied by @code{display-buffer-fallback-action} by reordering them or by adding actions that are not present there but fit more closely the user's editing practice. However, it can also be used to change the default behavior in a more profound way. Let's consider a user who, as a rule, prefers to display buffers on another frame. Such a user might provide the following customization: @example @group (customize-set-variable 'display-buffer-base-action '((display-buffer-reuse-window display-buffer-pop-up-frame) (reusable-frames . 0))) @end group @end example @noindent This setting will cause @code{display-buffer} to first try to find a window showing the buffer on a visible or iconified frame and, if no such frame exists, pop up a new frame. You can observe this behavior on a graphical system by typing @w{@kbd{C-x 1}} in the window showing @file{*scratch*} and evaluating our canonical @code{display-buffer} form. This will usually create (and give focus to) a new frame whose root window shows @file{*foo*}. Iconify that frame and evaluate the canonical form again: @code{display-buffer} will reuse the window on the new frame (usually raising the frame and giving it focus too). Only if creating a new frame fails, @code{display-buffer} will apply the actions supplied by @code{display-buffer-fallback-action} which means to again try reusing a window, popping up a new window and so on. A trivial way to make frame creation fail is supplied by the following form: @example @group (let ((pop-up-frame-function 'ignore)) (display-buffer (get-buffer-create "*foo*"))) @end group @end example @noindent We will forget about that form immediately after observing that it fails to create a new frame and uses a fallback action instead. Note that @code{display-buffer-reuse-window} appears redundant in the customization of @code{display-buffer-base-action} because it is already part of @code{display-buffer-fallback-action} and should be tried there anyway. However, that would fail because due to the precedence of @code{display-buffer-base-action} over @code{display-buffer-fallback-action}, at that time @code{display-buffer-pop-up-frame} would have already won the race. In fact, this: @example @group (customize-set-variable 'display-buffer-base-action '(display-buffer-pop-up-frame (reusable-frames . 0))) @end group @end example @noindent would cause @code{display-buffer} to @emph{always} pop up a new frame which is probably not what our user wants. So far, we have only shown how @emph{users} can customize the default behavior of @code{display-buffer}. Let us now see how @emph{applications} can change the course of @code{display-buffer}. The canonical way to do that is to use the @var{action} argument of @code{display-buffer} or a function that calls it, like, for example, @code{pop-to-buffer} (@pxref{Switching Buffers}). Suppose an application wants to display @file{*foo*} preferably below the selected window (to immediately attract the attention of the user to the new window) or, if that fails, in a window at the bottom of the frame. It could do that with a call like this: @example @group (display-buffer (get-buffer-create "*foo*") '((display-buffer-below-selected display-buffer-at-bottom))) @end group @end example @noindent In order to see how this new, modified form works, delete any frame showing @file{*foo*}, type @w{@kbd{C-x 1}} followed by @w{@kbd{C-x 2}} in the window showing @file{*scratch*}, and subsequently evaluate that form. @code{display-buffer} should split the upper window, and show @file{*foo*} in the new window. Alternatively, if after @w{@kbd{C-x 2}} you had typed @w{@kbd{C-x o}}, @code{display-buffer} would have split the window at the bottom instead. Suppose now that, before evaluating the new form, you have made the selected window as small as possible, for example, by evaluating the form @code{(fit-window-to-buffer)} in that window. In that case, @code{display-buffer} would have failed to split the selected window and would have split the frame's root window instead, effectively displaying @file{*foo*} at the bottom of the frame. In either case, evaluating the new form a second time should reuse the window already showing @file{*foo*} since both functions supplied by the @var{action} argument try to reuse such a window first. By setting the @var{action} argument, an application effectively overrules any customization of @code{display-buffer-base-action}. Our user can now either accept the choice of the application, or redouble by customizing the option @code{display-buffer-alist} as follows: @example @group (customize-set-variable 'display-buffer-alist '(("\\*foo\\*" (display-buffer-reuse-window display-buffer-pop-up-frame)))) @end group @end example @noindent Trying this with the new, modified form above in a configuration that does not show @file{*foo*} anywhere, will display @file{*foo*} on a separate frame, completely ignoring the @var{action} argument of @code{display-buffer}. Note that we didn't care to specify a @code{reusable-frames} action alist entry in our specification of @code{display-buffer-alist}. @code{display-buffer} always takes the first one it finds---in our case the one specified by @code{display-buffer-base-action}. If we wanted to use a different specification, for example, to exclude iconified frames showing @file{*foo*} from the list of reusable ones, we would have to specify that separately, however: @example @group (customize-set-variable 'display-buffer-alist '(("\\*foo\\*" (display-buffer-reuse-window display-buffer-pop-up-frame) (reusable-frames . visible)))) @end group @end example @noindent If you try this, you will notice that repeated attempts to display @file{*foo*} will succeed to reuse a frame only if that frame is visible. The above example would allow the conclusion that users customize @code{display-buffer-alist} for the sole purpose to overrule the @var{action} argument chosen by applications. Such a conclusion would be incorrect. @code{display-buffer-alist} is the standard option for users to direct the course of display of specific buffers in a preferred way regardless of whether the display is also guided by an @var{action} argument. We can, however, reasonably conclude that customizing @code{display-buffer-alist} differs from customizing @code{display-buffer-base-action} in two major aspects: it is stronger because it overrides the @var{action} argument of @code{display-buffer}, and it allows to explicitly specify the affected buffers. In fact, displaying other buffers is not affected in any way by a customization for @file{*foo*}. For example, @example (display-buffer (get-buffer-create "*bar*")) @end example @noindent continues being governed by the settings of @code{display-buffer-base-action} and @code{display-buffer-fallback-action} only. We could stop with our examples here but Lisp programs still have an ace up their sleeves which they can use to overrule any customization of @code{display-buffer-alist}. It's the variable @code{display-buffer-overriding-action} which they can bind around @code{display-buffer} calls as follows: @example @group (let ((display-buffer-overriding-action '((display-buffer-same-window)))) (display-buffer (get-buffer-create "*foo*") '((display-buffer-below-selected display-buffer-at-bottom)))) @end group @end example @noindent Evaluating this form will usually display @file{*foo*} in the selected window regardless of the @var{action} argument and any user customizations. (Usually, an application will not bother to also provide an @var{action} argument. Here it just serves to illustrate the fact that it gets overridden.) It might be illustrative to look at the list of action functions @code{display-buffer} would have tried to display @file{*foo*} with the customizations we provided here. The list (including comments explaining who added this and the subsequent elements) is: @example @group (display-buffer-same-window ;; `display-buffer-overriding-action' display-buffer-reuse-window ;; `display-buffer-alist' display-buffer-pop-up-frame display-buffer-below-selected ;; ACTION argument display-buffer-at-bottom display-buffer-reuse-window ;; `display-buffer-base-action' display-buffer-pop-up-frame display-buffer--maybe-same-window ;; `display-buffer-fallback-action' display-buffer-reuse-window display-buffer--maybe-pop-up-frame-or-window display-buffer-in-previous-window display-buffer-use-some-window display-buffer-pop-up-frame) @end group @end example @noindent Note that among the internal functions listed here, @code{display-buffer--maybe-same-window} is effectively ignored while @code{display-buffer--maybe-pop-up-frame-or-window} actually runs @code{display-buffer-pop-up-window}. The action alist passed in each function call is: @example @group ((reusable-frames . visible) (reusable-frames . 0)) @end group @end example @noindent which shows that we have used the second specification of @code{display-buffer-alist} above, overriding the specification supplied by @code{display-buffer-base-action}. Suppose our user had written that as @example @group (customize-set-variable 'display-buffer-alist '(("\\*foo\\*" (display-buffer-reuse-window display-buffer-pop-up-frame) (inhibit-same-window . t) (reusable-frames . visible)))) @end group @end example @noindent In this case the @code{inhibit-same-window} alist entry will successfully invalidate the @code{display-buffer-same-window} specification from @code{display-buffer-overriding-action} and @code{display-buffer} will show @file{*foo*} on another frame. To make @code{display-buffer-overriding-action} more robust in this regard, the application would have to specify an appropriate @code{inhibit-same-window} entry too, for example, as follows: @example @group (let ((display-buffer-overriding-action '(display-buffer-same-window (inhibit-same-window . nil)))) (display-buffer (get-buffer-create "*foo*"))) @end group @end example @noindent This last example shows that while the precedence order of action functions is fixed, as described in @ref{Choosing Window}, an action alist entry specified by a display action ranked lower in that order can affect the execution of a higher ranked display action. @node The Zen of Buffer Display @subsection The Zen of Buffer Display @cindex guidelines for buffer display @cindex writing buffer display actions @cindex buffer display conventions In its most simplistic form, a frame accommodates always one single window that can be used for displaying a buffer. As a consequence, it is always the latest call of @code{display-buffer} that will have succeeded in placing its buffer there. Since working with such a frame is not very practical, Emacs by default allows for more complex frame layouts controlled by the default values of the frame size and the @code{split-height-threshold} and @code{split-width-threshold} options. Displaying a buffer not yet shown on a frame then either splits the single window on that frame or (re-)uses one of its two windows. The default behavior is abandoned as soon as the user customizes one of these thresholds or manually changes the frame's layout. The default behavior is also abandoned when calling @code{display-buffer} with a non-@code{nil} @var{action} argument or the user customizes one of the options mentioned in the previous subsections. Mastering @code{display-buffer} soon may become a frustrating experience due to the plethora of applicable display actions and the resulting frame layouts. However, refraining from using buffer display functions and falling back on a split & delete windows metaphor is not a good idea either. Buffer display functions give Lisp programs and users a framework to reconcile their different needs; no comparable framework exists for splitting and deleting windows. Buffer display functions also allow to at least partially restore the layout of a frame when removing a buffer from it later (@pxref{Quitting Windows}). Below we will give a number of guidelines to redeem the frustration mentioned above and thus to avoid literally losing buffers in-between the windows of a frame. @table @asis @item Write display actions without stress Writing display actions can be a pain because one has to lump together action functions and action alists in one huge list. (Historical reasons prevented us from having @code{display-buffer} support separate arguments for these.) It might help to memorize some basic forms like the ones listed below: @example '(nil (inhibit-same-window . t)) @end example @noindent specifies an action alist entry only and no action function. Its sole purpose is to inhibit a @code{display-buffer-same-window} function specified elsewhere from showing the buffer in the same window, see also the last example of the preceding subsection. @example '(display-buffer-below-selected) @end example @noindent on the other hand, specifies one action function and an empty action alist. To combine the effects of the above two specifications one would write the form @example '(display-buffer-below-selected (inhibit-same-window . t)) @end example @noindent to add another action function one would write @example @group '((display-buffer-below-selected display-buffer-at-bottom) (inhibit-same-window . t)) @end group @end example @noindent and to add another alist entry one would write @example @group '((display-buffer-below-selected display-buffer-at-bottom) (inhibit-same-window . t) (window-height . fit-window-to-buffer)) @end group @end example @noindent That last form can be used as @var{action} argument of @code{display-buffer} in the following way: @example @group (display-buffer (get-buffer-create "*foo*") '((display-buffer-below-selected display-buffer-at-bottom) (inhibit-same-window . t) (window-height . fit-window-to-buffer))) @end group @end example @noindent In a customization of @code{display-buffer-alist} it would be used as follows: @example @group (customize-set-variable 'display-buffer-alist '(("\\*foo\\*" (display-buffer-below-selected display-buffer-at-bottom) (inhibit-same-window . t) (window-height . fit-window-to-buffer)))) @end group @end example @noindent To add a customization for a second buffer one would then write: @example @group (customize-set-variable 'display-buffer-alist '(("\\*foo\\*" (display-buffer-below-selected display-buffer-at-bottom) (inhibit-same-window . t) (window-height . fit-window-to-buffer)) ("\\*bar\\*" (display-buffer-reuse-window display-buffer-pop-up-frame) (reusable-frames . visible)))) @end group @end example @item Treat each other with respect @code{display-buffer-alist} and @code{display-buffer-base-action} are user options---Lisp programs must never set or rebind them. @code{display-buffer-overriding-action}, on the other hand, is reserved for applications---who seldom use that option and if they use it, then with utmost care. Older implementations of @code{display-buffer} frequently caused users and applications to fight over the settings of user options like @code{pop-up-frames} and @code{pop-up-windows} (@pxref{Choosing Window Options}). This was one major reason for redesigning @code{display-buffer}---to provide a clear framework specifying what users and applications should be allowed to do. Lisp programs must be prepared that user customizations may cause buffers to get displayed in an unexpected way. They should never assume in their subsequent behavior, that the buffer has been shown precisely the way they asked for in the @var{action} argument of @code{display-buffer}. Users should not pose too many and too severe restrictions on how arbitrary buffers get displayed. Otherwise, they will risk to lose the characteristics of showing a buffer for a certain purpose. Suppose a Lisp program has been written to compare different versions of a buffer in two windows side-by-side. If the customization of @code{display-buffer-alist} prescribes that any such buffer should be always shown in or below the selected window, the program will have a hard time to set up the desired window configuration via @code{display-buffer}. To specify a preference for showing an arbitrary buffer, users should customize @code{display-buffer-base-action}. An example of how users who prefer working with multiple frames would do that was given in the previous subsection. @code{display-buffer-alist} should be reserved for displaying specific buffers in a specific way. @item Consider reusing a window that already shows the buffer Generally, it's always a good idea for users and Lisp programmers to be prepared for the case that a window already shows the buffer in question and to reuse that window. In the preceding subsection we have shown that failing to do so properly may cause @code{display-buffer} to continuously pop up a new frame although a frame showing that buffer existed already. In a few cases only, it might be undesirable to reuse a window, for example, when a different portion of the buffer should be shown in that window. Hence, @code{display-buffer-reuse-window} is one action function that should be used as often as possible, both in @var{action} arguments and customizations. An @code{inhibit-same-window} entry in the @var{action} argument usually takes care of the most common case where reusing a window showing the buffer should be avoided---that where the window in question is the selected one. @item Attract focus to the window chosen This is a no-brainer for people working with multiple frames---the frame showing the buffer will automatically raise and get focus unless an @code{inhibit-switch-frame} entry forbids it. For single frame users this task can be considerably more difficult. In particular, @code{display-buffer-pop-up-window} and @code{display-buffer-use-some-window} can become obtrusive in this regard. They split or use a seemingly arbitrary (often the largest or least recently used) window, distracting the user's attention. Some Lisp programs therefore try to choose a window at the bottom of the frame, for example, in order to display the buffer in vicinity of the minibuffer window where the user is expected to answer a question related to the new window. For non-input related actions @code{display-buffer-below-selected} might be preferable because the selected window usually already has the user's attention. @item Handle subsequent invocations of @code{display-buffer} @code{display-buffer} is not overly well suited for displaying several buffers in sequence and making sure that all these buffers are shown orderly in the resulting window configuration. Again, the standard action functions @code{display-buffer-pop-up-window} and @code{display-buffer-use-some-window} are not very suited for this purpose due to their somewhat chaotic nature in more complex configurations. To produce a window configuration displaying multiple buffers (or different views of one and the same buffer) in one and the same display cycle, Lisp programmers will unavoidably have to write their own action functions. A few tricks listed below might help in this regard. @itemize @bullet @item Making windows atomic (@pxref{Atomic Windows}) avoids breaking an existing window composition when popping up a new window. The new window will pop up outside the composition instead. @item Temporarily dedicating windows to their buffers (@pxref{Dedicated Windows}) avoids using a window for displaying a different buffer. A non-dedicated window will be used instead. @item Calling @code{window-preserve-size} (@pxref{Preserving Window Sizes}) will try to keep the size of the argument window unchanged when popping up a new window. You have to make sure that another window in the same combination can be shrunk instead, though. @item Side windows (@pxref{Side Windows}) can be used for displaying specific buffers always in a window at the same position of a frame. This permits grouping buffers that do not compete for being shown at the same time on a frame and showing any such buffer in the same window without disrupting the display of other buffers. @item Child frames (@pxref{Child Frames}) can be used to display a buffer within the screen estate of the selected frame without disrupting that frame's window configuration and without the overhead associated with full-fledged frames as inflicted by @code{display-buffer-pop-up-frame}. @end itemize @end table @node Window History @section Window History @cindex window history Each window remembers in a list the buffers it has previously displayed, and the order in which these buffers were removed from it. This history is used, for example, by @code{replace-buffer-in-windows} (@pxref{Buffers and Windows}), and when quitting windows (@pxref{Quitting Windows}). The list is automatically maintained by Emacs, but you can use the following functions to explicitly inspect or alter it: @defun window-prev-buffers &optional window This function returns a list specifying the previous contents of @var{window}. The optional argument @var{window} should be a live window and defaults to the selected one. Each list element has the form @code{(@var{buffer} @var{window-start} @var{window-pos})}, where @var{buffer} is a buffer previously shown in the window, @var{window-start} is the window start position (@pxref{Window Start and End}) when that buffer was last shown, and @var{window-pos} is the point position (@pxref{Window Point}) when that buffer was last shown in @var{window}. The list is ordered so that earlier elements correspond to more recently-shown buffers, and the first element usually corresponds to the buffer most recently removed from the window. @end defun @defun set-window-prev-buffers window prev-buffers This function sets @var{window}'s previous buffers to the value of @var{prev-buffers}. The argument @var{window} must be a live window and defaults to the selected one. The argument @var{prev-buffers} should be a list of the same form as that returned by @code{window-prev-buffers}. @end defun In addition, each window maintains a list of @dfn{next buffers}, which is a list of buffers re-shown by @code{switch-to-prev-buffer} (see below). This list is mainly used by @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} for choosing buffers to switch to. @defun window-next-buffers &optional window This function returns the list of buffers recently re-shown in @var{window} via @code{switch-to-prev-buffer}. The @var{window} argument must denote a live window or @code{nil} (meaning the selected window). @end defun @defun set-window-next-buffers window next-buffers This function sets the next buffer list of @var{window} to @var{next-buffers}. The @var{window} argument should be a live window or @code{nil} (meaning the selected window). The argument @var{next-buffers} should be a list of buffers. @end defun The following commands can be used to cycle through the global buffer list, much like @code{bury-buffer} and @code{unbury-buffer}. However, they cycle according to the specified window's history list, rather than the global buffer list. In addition, they restore window-specific window start and point positions, and may show a buffer even if it is already shown in another window. The @code{switch-to-prev-buffer} command, in particular, is used by @code{replace-buffer-in-windows}, @code{bury-buffer} and @code{quit-window} to find a replacement buffer for a window. @deffn Command switch-to-prev-buffer &optional window bury-or-kill This command displays the previous buffer in @var{window}. The argument @var{window} should be a live window or @code{nil} (meaning the selected window). If the optional argument @var{bury-or-kill} is non-@code{nil}, this means that the buffer currently shown in @var{window} is about to be buried or killed and consequently should not be switched to in future invocations of this command. The previous buffer is usually the buffer shown before the buffer currently shown in @var{window}. However, a buffer that has been buried or killed, or has been already shown by a recent invocation of @code{switch-to-prev-buffer}, does not qualify as previous buffer. If repeated invocations of this command have already shown all buffers previously shown in @var{window}, further invocations will show buffers from the buffer list of the frame @var{window} appears on (@pxref{Buffer List}). The option @code{switch-to-prev-buffer-skip} described below can be used to inhibit switching to certain buffers, for example, to those already shown in another window. Also, if @var{window}'s frame has a @code{buffer-predicate} parameter (@pxref{Buffer Parameters}), that predicate may inhibit switching to certain buffers. @end deffn @deffn Command switch-to-next-buffer &optional window This command switches to the next buffer in @var{window}, thus undoing the effect of the last @code{switch-to-prev-buffer} command in @var{window}. The argument @var{window} must be a live window and defaults to the selected one. If there is no recent invocation of @code{switch-to-prev-buffer} that can be undone, this function tries to show a buffer from the buffer list of the frame @var{window} appears on (@pxref{Buffer List}). The option @code{switch-to-prev-buffer-skip} and the @code{buffer-predicate} (@pxref{Buffer Parameters}) of @var{window}'s frame affect this command as they do for @code{switch-to-prev-buffer}. @end deffn By default @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} can switch to a buffer that is already shown in another window. The following option can be used to override this behavior. @defopt switch-to-prev-buffer-skip If this variable is @code{nil}, @code{switch-to-prev-buffer} may switch to any buffer, including those already shown in other windows. If this variable is non-@code{nil}, @code{switch-to-prev-buffer} will refrain from switching to certain buffers. The following values can be used: @itemize @bullet @item @code{this} means do not switch to a buffer shown on the frame that hosts the window @code{switch-to-prev-buffer} is acting upon. @item @code{visible} means do not switch to a buffer shown on any visible frame. @item 0 (the number zero) means do not switch to a buffer shown on any visible or iconified frame. @item @code{t} means do not switch to a buffer shown on any live frame. @item A function that takes three arguments---the @var{window} argument of @code{switch-to-prev-buffer}, a buffer @code{switch-to-prev-buffer} intends to switch to and the @var{bury-or-kill} argument of @code{switch-to-prev-buffer}. If that function returns non-@code{nil}, @code{switch-to-prev-buffer} will refrain from switching to the buffer specified by the second argument. @end itemize The command @code{switch-to-next-buffer} obeys this option in a similar way. If this option specifies a function, @code{switch-to-next-buffer} will call that function with the third argument always @code{nil}. Note that since @code{switch-to-prev-buffer} is called by @code{bury-buffer}, @code{replace-buffer-in-windows} and @code{quit-restore-window} as well, customizing this option may also affect the behavior of Emacs when a window is quit or a buffer gets buried or killed. Note also that under certain circumstances @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} may ignore this option, for example, when there is only one buffer left these functions can switch to. @end defopt @node Dedicated Windows @section Dedicated Windows @cindex dedicated window Functions for displaying a buffer can be told to not use specific windows by marking these windows as @dfn{dedicated} to their buffers. @code{display-buffer} (@pxref{Choosing Window}) never uses a dedicated window for displaying another buffer in it. @code{get-lru-window} and @code{get-largest-window} (@pxref{Cyclic Window Ordering}) do not consider dedicated windows as candidates when their @var{dedicated} argument is non-@code{nil}. The behavior of @code{set-window-buffer} (@pxref{Buffers and Windows}) with respect to dedicated windows is slightly different, see below. Functions supposed to remove a buffer from a window or a window from a frame can behave specially when a window they operate on is dedicated. We will distinguish three basic cases, namely where (1) the window is not the only window on its frame, (2) the window is the only window on its frame but there are other frames on the same terminal left, and (3) the window is the only window on the only frame on the same terminal. In particular, @code{delete-windows-on} (@pxref{Deleting Windows}) handles case (2) by deleting the associated frame and case (3) by showing another buffer in that frame's only window. The function @code{replace-buffer-in-windows} (@pxref{Buffers and Windows}) which is called when a buffer gets killed, deletes the window in case (1) and behaves like @code{delete-windows-on} otherwise. @c FIXME: Does replace-buffer-in-windows _delete_ a window in case (1)? When @code{bury-buffer} (@pxref{Buffer List}) operates on the selected window (which shows the buffer that shall be buried), it handles case (2) by calling @code{frame-auto-hide-function} (@pxref{Quitting Windows}) to deal with the selected frame. The other two cases are handled as with @code{replace-buffer-in-windows}. @defun window-dedicated-p &optional window This function returns non-@code{nil} if @var{window} is dedicated to its buffer and @code{nil} otherwise. More precisely, the return value is the value assigned by the last call of @code{set-window-dedicated-p} for @var{window}, or @code{nil} if that function was never called with @var{window} as its argument. The default for @var{window} is the selected window. @end defun @defun set-window-dedicated-p window flag This function marks @var{window} as dedicated to its buffer if @var{flag} is non-@code{nil}, and non-dedicated otherwise. As a special case, if @var{flag} is @code{t}, @var{window} becomes @dfn{strongly} dedicated to its buffer. @code{set-window-buffer} signals an error when the window it acts upon is strongly dedicated to its buffer and does not already display the buffer it is asked to display. Other functions do not treat @code{t} differently from any non-@code{nil} value. @end defun You can also tell @code{display-buffer} to mark a window it creates as dedicated to its buffer by providing a suitable @code{dedicated} action alist entry (@pxref{Buffer Display Action Alists}). @node Quitting Windows @section Quitting Windows When you want to get rid of a window used for displaying a buffer, you can call @code{delete-window} or @code{delete-windows-on} (@pxref{Deleting Windows}) to remove that window from its frame. If the buffer is shown on a separate frame, you might want to call @code{delete-frame} (@pxref{Deleting Frames}) instead. If, on the other hand, a window has been reused for displaying the buffer, you might prefer showing the buffer previously shown in that window, by calling the function @code{switch-to-prev-buffer} (@pxref{Window History}). Finally, you might want to either bury (@pxref{Buffer List}) or kill (@pxref{Killing Buffers}) the window's buffer. The following command uses information on how the window for displaying the buffer was obtained in the first place, thus attempting to automate the above decisions for you. @deffn Command quit-window &optional kill window This command quits @var{window} and buries its buffer. The argument @var{window} must be a live window and defaults to the selected one. With prefix argument @var{kill} non-@code{nil}, it kills the buffer instead of burying it. It calls the function @code{quit-restore-window} described next to deal with the window and its buffer. @vindex quit-window-hook The functions in @code{quit-window-hook} are run before doing anything else. @end deffn @defun quit-restore-window &optional window bury-or-kill This function handles @var{window} and its buffer after quitting. The optional argument @var{window} must be a live window and defaults to the selected one. The function's behavior is determined by the four elements of the list specified by @var{window}'s @code{quit-restore} parameter (@pxref{Window Parameters}). The first element of the @code{quit-restore} parameter is one of the symbols @code{window}, meaning that the window has been specially created by @code{display-buffer}; @code{frame}, a separate frame has been created; @code{same}, the window has only ever displayed this buffer; or @code{other}, the window showed another buffer before. @code{frame} and @code{window} affect how the window is quit, while @code{same} and @code{other} affect the redisplay of buffers previously shown in @var{window}. The parameter's second element is either one of the symbols @code{window} or @code{frame}, or a list whose elements are the buffer shown in @var{window} before, that buffer's window start and window point positions, and @var{window}'s height at that time. If that buffer is still live when @var{window} is quit, then this function may reuse @var{window} to display it. The third element is the window selected at the time the parameter was created. If this function deletes @var{window}, it subsequently tries to reselect the window named by that element. The fourth element is the buffer whose display caused the creation of this parameter. This function may delete @var{window} if and only if it still shows that buffer. This function will try to delete @var{window} if and only if (1) the first element of its @code{quit-restore} parameter is either @code{window} or @code{frame}, (2) the window has no history of previously-displayed buffers and (3) the fourth element of the @code{quit-restore} parameter specifies the buffer currently displayed in @var{window}. If @var{window} is part of an atomic window (@pxref{Atomic Windows}), it will try to delete the root of that atomic window instead. In either case, it tries to avoid signaling an error when @var{window} cannot be deleted. If @var{window} shall be deleted, is the only window on its frame and there are other frames on that frame's terminal, the value of the optional argument @var{bury-or-kill} determines how to proceed with the window. If @var{bury-or-kill} equals @code{kill}, the frame is deleted unconditionally. Otherwise, the fate of the frame is determined by calling @code{frame-auto-hide-function} (see below) with that frame as sole argument. If the third element of the @code{quit-restore} parameter is a list of buffer, window start (@pxref{Window Start and End}), and point (@pxref{Window Point}), and that buffer is still live, the buffer will be displayed, and start and point set accordingly. If, in addition, @var{window}'s buffer was temporarily resized, this function will also try to restore the original height of @var{window}. Otherwise, if @var{window} was previously used for displaying other buffers (@pxref{Window History}), the most recent buffer in that history will be displayed. In either case, if @var{window} is not deleted, its @code{quit-restore} parameter is reset to @code{nil}. The optional argument @var{bury-or-kill} specifies how to deal with @var{window}'s buffer. The following values are handled: @table @code @item nil This means to not deal with the buffer in any particular way. As a consequence, if @var{window} is not deleted, invoking @code{switch-to-prev-buffer} will usually show the buffer again. @item append This means that if @var{window} is not deleted, its buffer is moved to the end of @var{window}'s list of previous buffers, so it's less likely that a future invocation of @code{switch-to-prev-buffer} will switch to it. Also, it moves the buffer to the end of the frame's buffer list. @item bury This means that if @var{window} is not deleted, its buffer is removed from @var{window}'s list of previous buffers. Also, it moves the buffer to the end of the frame's buffer list. This value provides the most reliable remedy to not have @code{switch-to-prev-buffer} switch to this buffer again without killing the buffer. @item kill This means to kill @var{window}'s buffer. @end table Typically, the display routines run by @code{display-buffer} will set the @code{quit-restore} window parameter correctly. It's also possible to set it manually, using the following code for displaying @var{buffer} in @var{window}: @example @group (display-buffer-record-window type window buffer) (set-window-buffer window buffer) (set-window-prev-buffers window nil) @end group @end example Setting the window history to @code{nil} ensures that a future call to @code{quit-window} can delete the window altogether. @end defun The following option specifies how to deal with a frame containing just one window that should be either quit, or whose buffer should be buried. @defopt frame-auto-hide-function The function specified by this option is called to automatically hide frames. This function is called with one argument---a frame. The function specified here is called by @code{bury-buffer} (@pxref{Buffer List}) when the selected window is dedicated and shows the buffer to bury. It is also called by @code{quit-restore-window} (see above) when the frame of the window to quit has been specially created for displaying that window's buffer and the buffer is not killed. The default is to call @code{iconify-frame} (@pxref{Visibility of Frames}). Alternatively, you may specify either @code{delete-frame} (@pxref{Deleting Frames}) to remove the frame from its display, @code{make-frame-invisible} to make the frame invisible, @code{ignore} to leave the frame unchanged, or any other function that can take a frame as its sole argument. Note that the function specified by this option is called only if the specified frame contains just one live window and there is at least one other frame on the same terminal. For a particular frame, the value specified here may be overridden by that frame's @code{auto-hide-function} frame parameter (@pxref{Frame Interaction Parameters}). @end defopt @node Side Windows @section Side Windows @cindex side windows @cindex main window @cindex main window of a frame Side windows are special windows positioned at any of the four sides of a frame's root window (@pxref{Windows and Frames}). In practice, this means that the area of the frame's root window is subdivided into a main window and a number of side windows surrounding that main window. The main window is either a ``normal'' live window or specifies the area containing all the normal windows. In their most simple form of use, side windows allow to display specific buffers always in the same area of a frame. Hence they can be regarded as a generalization of the concept provided by @code{display-buffer-at-bottom} (@pxref{Buffer Display Action Functions}) to the remaining sides of a frame. With suitable customizations, however, side windows can be also used to provide frame layouts similar to those found in so-called integrated development environments (IDEs). @menu * Displaying Buffers in Side Windows:: An action function for displaying buffers in side windows. * Side Window Options and Functions:: Further tuning of side windows. * Frame Layouts with Side Windows:: Setting up frame layouts with side windows. @end menu @node Displaying Buffers in Side Windows @subsection Displaying Buffers in Side Windows The following action function for @code{display-buffer} (@pxref{Buffer Display Action Functions}) creates or reuses a side window for displaying the specified buffer. @defun display-buffer-in-side-window buffer alist This function displays @var{buffer} in a side window of the selected frame. It returns the window used for displaying @var{buffer}, @code{nil} if no such window can be found or created. @var{alist} is an association list of symbols and values as for @code{display-buffer}. The following symbols in @var{alist} are special for this function: @table @code @item side Denotes the side of the frame where the window shall be located. Valid values are @code{left}, @code{top}, @code{right} and @code{bottom}. If unspecified, the window is located at the bottom of the frame. @item slot Denotes a slot at the specified side where to locate the window. A value of zero means to preferably position the window in the middle of the specified side. A negative value means to use a slot preceding (that is, above or on the left of) the middle slot. A positive value means to use a slot following (that is, below or on the right of) the middle slot. Hence, all windows on a specific side are ordered by their @code{slot} value. If unspecified, the window is located in the middle of the specified side. @end table If you specify the same slot on the same side for two or more different buffers, the buffer displayed last is shown in the corresponding window. Hence, slots can be used for sharing the same side window between buffers. This function installs the @code{window-side} and @code{window-slot} parameters (@pxref{Window Parameters}) and makes them persistent. It does not install any other window parameters unless they have been explicitly provided via a @code{window-parameters} entry in @var{alist}. @end defun By default, side windows cannot be split via @code{split-window} (@pxref{Splitting Windows}). Also, a side window is not reused or split by any buffer display action (@pxref{Buffer Display Action Functions}) unless it is explicitly specified as target of that action. Note also that @code{delete-other-windows} cannot make a side window the only window on its frame (@pxref{Deleting Windows}). Once set up, side windows also change the behavior of the commands @code{switch-to-prev-buffer} and @code{switch-to-next-buffer} (@pxref{Window History}). In particular, these commands will refrain from showing, in a side window, buffers that have not been displayed in that window before. They will also refrain from having a normal, non-side window show a buffer that has been already displayed in a side window. A notable exception to the latter rule occurs when an application, after displaying a buffer, resets that buffer's local variables. @node Side Window Options and Functions @subsection Side Window Options and Functions The following options provide additional control over the placement of side windows. @defopt window-sides-vertical If non-@code{nil}, the side windows on the left and right of a frame occupy the frame's full height. Otherwise, the side windows on the top and bottom of the frame occupy the frame's full width. @end defopt @defopt window-sides-slots This option specifies the maximum number of side windows on each side of a frame. The value is a list of four elements specifying the number of side window slots on (in this order) the left, top, right and bottom of each frame. If an element is a number, it means to display at most that many windows on the corresponding side. If an element is @code{nil}, it means there's no bound on the number of slots on that side. If any of the specified values is zero, no window can be created on the corresponding side. @code{display-buffer-in-side-window} will not signal an error in that case, but will return @code{nil}. If a specified value just forbids the creation of an additional side window, the most suitable window on that side is reused and may have its @code{window-slot} parameter changed accordingly. @end defopt @defopt window-sides-reversed This option specifies whether top/bottom side windows should appear in reverse order. When this is @code{nil}, side windows on the top and bottom of a frame are always drawn from left to right with increasing slot values. When this is @code{t}, the drawing order is reversed and side windows on the top and bottom of a frame are drawn from right to left with increasing slot values. When this is @code{bidi}, the drawing order is reversed if and only if the value of @code{bidi-paragraph-direction} (@pxref{Bidirectional Display}) is @code{right-to-left} in the buffer displayed in the window most recently selected within the main window area of this frame. Sometimes that window may be hard to find, so heuristics are used to avoid that the drawing order changes inadvertently when another window gets selected. The layout of side windows on the left or right of a frame is not affected by the value of this variable. @end defopt When a frame has side windows, the following function returns the main window of that frame. @defun window-main-window &optional frame This function returns the main window of the specified @var{frame}. The optional argument @var{frame} must be a live frame and defaults to the selected one. If @var{frame} has no side windows, it returns @var{frame}'s root window. Otherwise, it returns either an internal non-side window such that all other non-side windows on @var{frame} descend from it, or the single live non-side window of @var{frame}. Note that the main window of a frame cannot be deleted via @code{delete-window}. @end defun The following command is handy to toggle the appearance of all side windows on a specified frame. @deffn Command window-toggle-side-windows &optional frame This command toggles side windows on the specified @var{frame}. The optional argument @var{frame} must be a live frame and defaults to the selected one. If @var{frame} has at least one side window, this command saves the state of @var{frame}'s root window in the @var{frame}'s @code{window-state} frame parameter and deletes all side windows on @var{frame} afterwards. If @var{frame} has no side windows, but does have a @code{window-state} parameter, this command uses that parameter's value to restore the side windows on @var{frame} leaving @var{frame}'s main window alone. An error is signaled if @var{frame} has no side windows and no saved state is found for it. @end deffn @node Frame Layouts with Side Windows @subsection Frame Layouts with Side Windows Side windows can be used to create more complex frame layouts like those provided by integrated development environments (IDEs). In such layouts, the area of the main window is where the normal editing activities take place. Side windows are not conceived for editing in the usual sense. Rather, they are supposed to display information complementary to the current editing activity, like lists of files, tags or buffers, help information, search or grep results or shell output. The layout of such a frame might appear as follows: @smallexample @group ___________________________________ | *Buffer List* | |___________________________________| | | | | | * | | * | | d | | T | | i | | a | | r | Main Window Area | g | | e | | s | | d | | * | | * | | | |_____|_______________________|_____| | *help*/*grep*/ | *shell*/ | | *Completions* | *compilation* | |_________________|_________________| | Echo Area | |___________________________________| @end group @end smallexample The following example illustrates how window parameters (@pxref{Window Parameters}) can be used with @code{display-buffer-in-side-window} (@pxref{Displaying Buffers in Side Windows}) to set up code for producing the frame layout sketched above. @example @group (defvar parameters '(window-parameters . ((no-other-window . t) (no-delete-other-windows . t)))) (setq fit-window-to-buffer-horizontally t) (setq window-resize-pixelwise t) (setq display-buffer-alist `(("\\*Buffer List\\*" display-buffer-in-side-window (side . top) (slot . 0) (window-height . fit-window-to-buffer) (preserve-size . (nil . t)) ,parameters) ("\\*Tags List\\*" display-buffer-in-side-window (side . right) (slot . 0) (window-width . fit-window-to-buffer) (preserve-size . (t . nil)) ,parameters) ("\\*\\(?:help\\|grep\\|Completions\\)\\*" display-buffer-in-side-window (side . bottom) (slot . -1) (preserve-size . (nil . t)) ,parameters) ("\\*\\(?:shell\\|compilation\\)\\*" display-buffer-in-side-window (side . bottom) (slot . 1) (preserve-size . (nil . t)) ,parameters))) @end group @end example This specifies @code{display-buffer-alist} entries (@pxref{Choosing Window}) for buffers with fixed names. In particular, it asks for showing @file{*Buffer List*} with adjustable height at the top of the frame and @file{*Tags List*} with adjustable width on the frame's right. It also asks for having the @file{*help*}, @file{*grep*} and @file{*Completions*} buffers share a window on the bottom left side of the frame and the @file{*shell*} and @file{*compilation*} buffers appear in a window on the bottom right side of the frame. Note that the option @code{fit-window-to-buffer-horizontally} must have a non-@code{nil} value in order to allow horizontal adjustment of windows. Entries are also added that ask for preserving the height of side windows at the top and bottom of the frame and the width of side windows at the left or right of the frame. To assure that side windows retain their respective sizes when maximizing the frame, the variable @code{window-resize-pixelwise} is set to a non-@code{nil} value. @xref{Resizing Windows}. The last form also makes sure that none of the created side windows are accessible via @w{@kbd{C-x o}} by installing the @code{no-other-window} parameter for each of these windows. In addition, it makes sure that side windows are not deleted via @w{@kbd{C-x 1}} by installing the @code{no-delete-other-windows} parameter for each of these windows. Since @code{dired} buffers have no fixed names, we use a special function @code{dired-default-directory-on-left} in order to display a lean directory buffer on the left side of the frame. @example @group (defun dired-default-directory-on-left () "Display `default-directory' in side window on left, hiding details." (interactive) (let ((buffer (dired-noselect default-directory))) (with-current-buffer buffer (dired-hide-details-mode t)) (display-buffer-in-side-window buffer `((side . left) (slot . 0) (window-width . fit-window-to-buffer) (preserve-size . (t . nil)) ,parameters)))) @end group @end example Evaluating the preceding forms and typing, in any order, @w{@kbd{M-x list-buffers}}, @kbd{C-h f}, @kbd{M-x shell}, @w{@kbd{M-x list-tags}}, and @kbd{M-x dired-default-directory-on-left} should now reproduce the frame layout sketched above. @node Atomic Windows @section Atomic Windows @cindex atomic windows Atomic windows are rectangular compositions of at least two live windows. They have the following distinctive characteristics: @itemize @bullet @item The function @code{split-window} (@pxref{Splitting Windows}), when applied to a constituent of an atomic window, will try to create the new window outside of the atomic window. @item The function @code{delete-window} (@pxref{Deleting Windows}), when applied to a constituent of an atomic window, will try to delete the entire atomic window instead. @item The function @code{delete-other-windows} (@pxref{Deleting Windows}), when applied to a constituent of an atomic window, will try to make the atomic window fill its frame or main window (@pxref{Side Windows}). @end itemize This means that the basic groups of functions that alter the window structure treat an atomic window like a live one, thus preserving the internal structure of the atomic window. Atomic windows are useful to construct and preserve window layouts that are meaningful only when all involved buffers are shown simultaneously in a specific manner, such as when showing differences between file revisions, or the same text in different languages or markups. They can also be used to permanently display information pertinent to a specific window in bars on that window's sides. @cindex root window of atomic window Atomic windows are implemented with the help of the reserved @code{window-atom} window parameter (@pxref{Window Parameters}) and an internal window (@pxref{Basic Windows}) called the root window of the atomic window. All windows that are part of the same atomic window have this root window as their common ancestor and are assigned a non-@code{nil} @code{window-atom} parameter. The following function returns the root of the atomic window a specified window is part of: @defun window-atom-root &optional window This functions returns the root of the atomic window @var{window} is a part of. The specified @var{window} must be a valid window and defaults to the selected one. It returns @code{nil} if @var{window} is not part of an atomic window. @end defun The most simple approach to make a new atomic window is to take an existing internal window and apply the following function: @defun window-make-atom window This function converts @var{window} into an atomic window. The specified @var{window} must be an internal window. All this function does is to set the @code{window-atom} parameter of each descendant of @var{window} to @code{t}. @end defun To create a new atomic window from an existing live window or to add a new window to an existing atomic window, the following buffer display action function (@pxref{Buffer Display Action Functions}) can be used: @defun display-buffer-in-atom-window buffer alist This function tries to display @var{buffer} in a new window that will be combined with an existing window to form an atomic window. If the existing window is already part of an atomic window, it adds the new window to that atomic window. The specified @var{alist} is an association list of symbols and values. The following symbols have a special meaning: @table @code @item window The value of such an element specifies an existing window the new window shall be combined with. If it specifies an internal window, all children of that window become part of the atomic window too. If no window is specified, the new window becomes a sibling of the selected window. The @code{window-atom} parameter of the existing window is set to @code{main} provided that window is live and its @code{window-atom} parameter was not already set. @item side The value of such an element denotes the side of the existing window where the new window shall be located. Valid values are @code{below}, @code{right}, @code{above} and @code{left}. The default is @code{below}. The @code{window-atom} parameter of the new window is set to this value. @end table The return value is the new window, @code{nil} when creating that window failed. @end defun Note that the value of the @code{window-atom} parameter does not really matter as long as it is non-@code{nil}. The values assigned by @code{display-buffer-in-atom-window} just allow for easy retrieval of the original and the new window after that function has been applied. Note also that the @code{window-atom} parameter is the only window parameter assigned by @code{display-buffer-in-atom-window}. Further parameters have to be set by the application explicitly via a @code{window-parameters} entry in @var{alist}. Atomic windows automatically cease to exist when one of their constituents gets deleted. To dissolve an atomic window manually, reset the @code{window-atom} parameter of its constituents---the root of the atomic window and all its descendants. The following code snippet, when applied to a single-window frame, first splits the selected window and makes the selected and the new window constituents of an atomic window with their parent as root. It then displays the buffer @file{*Messages*} in a new window at the frame's bottom and makes that new window part of the atomic window just created. @example @group (let ((window (split-window-right))) (window-make-atom (window-parent window)) (display-buffer-in-atom-window (get-buffer-create "*Messages*") `((window . ,(window-parent window)) (window-height . 5)))) @end group @end example At this moment typing @w{@kbd{C-x 2}} in any window of that frame produces a new window at the bottom of the frame. Typing @w{@kbd{C-x 3}} instead will put the new window at the frame's right. In either case, typing now @w{@kbd{C-x 1}} in any window of the atomic window will remove the new window only. Typing @w{@kbd{C-x 0}} in any window of the atomic window will make that new window fill the frame. @node Window Point @section Windows and Point @cindex window position @cindex window point @cindex position in window @cindex point in window Each window has its own value of point (@pxref{Point}), independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer. @itemize @bullet @item The window point is established when a window is first created; it is initialized from the buffer's point, or from the window point of another window opened on the buffer if such a window exists. @item Selecting a window sets the value of point in its buffer from the window's value of point. Conversely, deselecting a window sets the window's value of point from that of the buffer. Thus, when you switch between windows that display a given buffer, the point value for the selected window is in effect in the buffer, while the point values for the other windows are stored in those windows. @item As long as the selected window displays the current buffer, the window's point and the buffer's point always move together; they remain equal. @end itemize @cindex cursor Emacs displays the cursor, by default as a rectangular block, in each window at the position of that window's point. When the user switches to another buffer in a window, Emacs moves that window's cursor to where point is in that buffer. If the exact position of point is hidden behind some display element, such as a display string or an image, Emacs displays the cursor immediately before or after that display element. @defun window-point &optional window This function returns the current position of point in @var{window}. For a nonselected window, this is the value point would have (in that window's buffer) if that window were selected. The default for @var{window} is the selected window. When @var{window} is the selected window, the value returned is the value of point in that window's buffer. Strictly speaking, it would be more correct to return the top-level value of point, outside of any @code{save-excursion} forms. But that value is hard to find. @end defun @defun set-window-point window position This function positions point in @var{window} at position @var{position} in @var{window}'s buffer. It returns @var{position}. If @var{window} is selected, this simply does @code{goto-char} in @var{window}'s buffer. @end defun @defvar window-point-insertion-type This variable specifies the marker insertion type (@pxref{Marker Insertion Types}) of @code{window-point}. The default is @code{nil}, so @code{window-point} will stay behind text inserted there. @end defvar @node Window Start and End @section The Window Start and End Positions @cindex window start position @cindex display-start position Each window maintains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the @dfn{display-start} position of the window (or just the @dfn{start}). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line. After switching windows or buffers, and in some other cases, if the window start is in the middle of a line, Emacs adjusts the window start to the start of a line. This prevents certain operations from leaving the window start at a meaningless point within a line. This feature may interfere with testing some Lisp code by executing it using the commands of Lisp mode, because they trigger this readjustment. To test such code, put it into a command and bind the command to a key. @defun window-start &optional window @cindex window top line This function returns the display-start position of window @var{window}. If @var{window} is @code{nil}, the selected window is used. When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or to @code{point-min} if the buffer doesn't have any. Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)---to make sure point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay. @end defun @defun window-group-start &optional window @vindex window-group-start-function This function is like @code{window-start}, except that when @var{window} is a part of a group of windows (@pxref{Window Group}), @code{window-group-start} returns the start position of the entire group. This condition holds when the buffer local variable @code{window-group-start-function} is set to a function. In this case, @code{window-group-start} calls the function with the single argument @var{window}, then returns its result. @end defun @cindex window end position @cindex last visible position in a window @defun window-end &optional window update This function returns the position where display of its buffer ends in @var{window}. The default for @var{window} is the selected window. Simply changing the buffer text or moving point does not update the value that @code{window-end} returns. The value is updated only when Emacs redisplays and redisplay completes without being preempted. If the last redisplay of @var{window} was preempted, and did not finish, Emacs does not know the position of the end of display in that window. In that case, this function returns @code{nil}. If @var{update} is non-@code{nil}, @code{window-end} always returns an up-to-date value for where display ends, based on the current @code{window-start} value. If a previously saved value of that position is still valid, @code{window-end} returns that value; otherwise it computes the correct value by scanning the buffer text. Even if @var{update} is non-@code{nil}, @code{window-end} does not attempt to scroll the display if point has moved off the screen, the way real redisplay would do. It does not alter the @code{window-start} value. In effect, it reports where the displayed text will end if scrolling is not required. Note that the position it returns might be only partially visible. @end defun @vindex window-group-end-function @defun window-group-end &optional window update This function is like @code{window-end}, except that when @var{window} is a part of a group of windows (@pxref{Window Group}), @code{window-group-end} returns the end position of the entire group. This condition holds when the buffer local variable @code{window-group-end-function} is set to a function. In this case, @code{window-group-end} calls the function with the two arguments @var{window} and @var{update}, then returns its result. The argument @var{update} has the same meaning as in @code{window-end}. @end defun @defun set-window-start window position &optional noforce This function sets the display-start position of @var{window} to @var{position} in @var{window}'s buffer. It returns @var{position}. The display routines insist that the position of point be visible when a buffer is displayed. Normally, they select the display-start position according to their internal logic (and scroll the window if necessary) to make point visible. However, if you specify the start position with this function using @code{nil} for @var{noforce}, it means you want display to start at @var{position} even if that would put the location of point off the screen. If this does place point off screen, the display routines attempt to move point to the left margin on the middle line in the window. For example, if point @w{is 1} and you set the start of the window @w{to 37}, the start of the next line, point will be above the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example: @example @group ;; @r{Here is what @samp{foo} looks like before executing} ;; @r{the @code{set-window-start} expression.} @end group @group ---------- Buffer: foo ---------- @point{}This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- @end group @group (set-window-start (selected-window) (save-excursion (goto-char 1) (forward-line 1) (point))) @result{} 37 @end group @group ;; @r{Here is what @samp{foo} looks like after executing} ;; @r{the @code{set-window-start} expression.} ---------- Buffer: foo ---------- 2 3 @point{}4 5 6 ---------- Buffer: foo ---------- @end group @end example If the attempt to make point visible (i.e., in a fully-visible screen line) fails, the display routines will disregard the requested window-start position and compute a new one anyway. Thus, for reliable results Lisp programs that call this function should always move point to be inside the window whose display starts at @var{position}. If @var{noforce} is non-@code{nil}, and @var{position} would place point off screen at the next redisplay, then redisplay computes a new window-start position that works well with point, and thus @var{position} is not used. @end defun @vindex set-window-group-start-function @defun set-window-group-start window position &optional noforce This function is like @code{set-window-start}, except that when @var{window} is a part of a group of windows (@pxref{Window Group}), @code{set-window-group-start} sets the start position of the entire group. This condition holds when the buffer local variable @code{set-window-group-start-function} is set to a function. In this case, @code{set-window-group-start} calls the function with the three arguments @var{window}, @var{position}, and @var{noforce}, then returns its result. The arguments @var{position} and @var{noforce} in this function have the same meaning as in @code{set-window-start}. @end defun @defun pos-visible-in-window-p &optional position window partially This function returns non-@code{nil} if @var{position} is within the range of text currently visible on the screen in @var{window}. It returns @code{nil} if @var{position} is scrolled vertically out of view. Locations that are partially obscured are not considered visible unless @var{partially} is non-@code{nil}. The argument @var{position} defaults to the current position of point in @var{window}; @var{window} defaults to the selected window. If @var{position} is @code{t}, that means to check either the first visible position of the last screen line in @var{window}, or the end-of-buffer position, whichever comes first. This function considers only vertical scrolling. If @var{position} is out of view only because @var{window} has been scrolled horizontally, @code{pos-visible-in-window-p} returns non-@code{nil} anyway. @xref{Horizontal Scrolling}. If @var{position} is visible, @code{pos-visible-in-window-p} returns @code{t} if @var{partially} is @code{nil}; if @var{partially} is non-@code{nil}, and the character following @var{position} is fully visible, it returns a list of the form @code{(@var{x} @var{y})}, where @var{x} and @var{y} are the pixel coordinates relative to the top left corner of the window; otherwise it returns an extended list of the form @code{(@var{x} @var{y} @var{rtop} @var{rbot} @var{rowh} @var{vpos})}, where @var{rtop} and @var{rbot} specify the number of off-window pixels at the top and bottom of the row at @var{position}, @var{rowh} specifies the visible height of that row, and @var{vpos} specifies the vertical position (zero-based row number) of that row. Here is an example: @example @group ;; @r{If point is off the screen now, recenter it now.} (or (pos-visible-in-window-p (point) (selected-window)) (recenter 0)) @end group @end example @end defun @vindex pos-visible-in-window-group-p-function @defun pos-visible-in-window-group-p &optional position window partially This function is like @code{pos-visible-in-window-p}, except that when @var{window} is a part of a group of windows (@pxref{Window Group}), @code{pos-visible-in-window-group-p} tests the visibility of @var{pos} in the entire group, not just in the single @var{window}. This condition holds when the buffer local variable @code{pos-visible-in-window-group-p-function} is set to a function. In this case @code{pos-visible-in-window-group-p} calls the function with the three arguments @var{position}, @var{window}, and @var{partially}, then returns its result. The arguments @var{position} and @var{partially} have the same meaning as in @code{pos-visible-in-window-p}. @end defun @defun window-line-height &optional line window This function returns the height of text line @var{line} in @var{window}. If @var{line} is one of @code{header-line} or @code{mode-line}, @code{window-line-height} returns information about the corresponding line of the window. Otherwise, @var{line} is a text line number starting from 0. A negative number counts from the end of the window. The default for @var{line} is the current line in @var{window}; the default for @var{window} is the selected window. If the display is not up to date, @code{window-line-height} returns @code{nil}. In that case, @code{pos-visible-in-window-p} may be used to obtain related information. If there is no line corresponding to the specified @var{line}, @code{window-line-height} returns @code{nil}. Otherwise, it returns a list @code{(@var{height} @var{vpos} @var{ypos} @var{offbot})}, where @var{height} is the height in pixels of the visible part of the line, @var{vpos} and @var{ypos} are the vertical position in lines and pixels of the line relative to the top of the first text line, and @var{offbot} is the number of off-window pixels at the bottom of the text line. If there are off-window pixels at the top of the (first) text line, @var{ypos} is negative. @end defun @node Textual Scrolling @section Textual Scrolling @cindex textual scrolling @cindex scrolling textually @dfn{Textual scrolling} means moving the text up or down through a window. It works by changing the window's display-start location. It may also change the value of @code{window-point} to keep point on the screen (@pxref{Window Point}). The basic textual scrolling functions are @code{scroll-up} (which scrolls forward) and @code{scroll-down} (which scrolls backward). In these function names, ``up'' and ``down'' refer to the direction of motion of the buffer text relative to the window. Imagine that the text is written on a long roll of paper and that the scrolling commands move the paper up and down. Thus, if you are looking at the middle of a buffer and repeatedly call @code{scroll-down}, you will eventually see the beginning of the buffer. Unfortunately, this sometimes causes confusion, because some people tend to think in terms of the opposite convention: they imagine the window moving over text that remains in place, so that ``down'' commands take you to the end of the buffer. This convention is consistent with fact that such a command is bound to a key named @key{PageDown} on modern keyboards. @ignore We have not switched to this convention as that is likely to break existing Emacs Lisp code. @end ignore Textual scrolling functions (aside from @code{scroll-other-window}) have unpredictable results if the current buffer is not the one displayed in the selected window. @xref{Current Buffer}. If the window contains a row taller than the height of the window (for example in the presence of a large image), the scroll functions will adjust the window's vertical scroll position to scroll the partially visible row. Lisp callers can disable this feature by binding the variable @code{auto-window-vscroll} to @code{nil} (@pxref{Vertical Scrolling}). @deffn Command scroll-up &optional count This function scrolls forward by @var{count} lines in the selected window. If @var{count} is negative, it scrolls backward instead. If @var{count} is @code{nil} (or omitted), the distance scrolled is @code{next-screen-context-lines} lines less than the height of the window's text area. If the selected window cannot be scrolled any further, this function signals an error. Otherwise, it returns @code{nil}. @end deffn @deffn Command scroll-down &optional count This function scrolls backward by @var{count} lines in the selected window. If @var{count} is negative, it scrolls forward instead. In other respects, it behaves the same way as @code{scroll-up} does. @end deffn @deffn Command scroll-up-command &optional count This behaves like @code{scroll-up}, except that if the selected window cannot be scrolled any further and the value of the variable @code{scroll-error-top-bottom} is @code{t}, it tries to move to the end of the buffer instead. If point is already there, it signals an error. @end deffn @deffn Command scroll-down-command &optional count This behaves like @code{scroll-down}, except that if the selected window cannot be scrolled any further and the value of the variable @code{scroll-error-top-bottom} is @code{t}, it tries to move to the beginning of the buffer instead. If point is already there, it signals an error. @end deffn @deffn Command scroll-other-window &optional count This function scrolls the text in another window upward @var{count} lines. Negative values of @var{count}, or @code{nil}, are handled as in @code{scroll-up}. You can specify which buffer to scroll by setting the variable @code{other-window-scroll-buffer} to a buffer. If that buffer isn't already displayed, @code{scroll-other-window} displays it in some window. When the selected window is the minibuffer, the next window is normally the leftmost one immediately above it. You can specify a different window to scroll, when the minibuffer is selected, by setting the variable @code{minibuffer-scroll-window}. This variable has no effect when any other window is selected. When it is non-@code{nil} and the minibuffer is selected, it takes precedence over @code{other-window-scroll-buffer}. @xref{Definition of minibuffer-scroll-window}. When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case, @code{scroll-other-window} attempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message @samp{End of buffer}. @end deffn @deffn Command scroll-other-window-down &optional count This function scrolls the text in another window downward @var{count} lines. Negative values of @var{count}, or @code{nil}, are handled as in @code{scroll-down}. In other respects, it behaves the same way as @code{scroll-other-window} does. @end deffn @defvar other-window-scroll-buffer If this variable is non-@code{nil}, it tells @code{scroll-other-window} which buffer's window to scroll. @end defvar @defopt scroll-margin This option specifies the size of the scroll margin---a minimum number of lines between point and the top or bottom of a window. Whenever point gets within this many lines of the top or bottom of the window, redisplay scrolls the text automatically (if possible) to move point out of the margin, closer to the center of the window. @end defopt @defopt maximum-scroll-margin This variable limits the effective value of @code{scroll-margin} to a fraction of the current window line height. For example, if the current window has 20 lines and @code{maximum-scroll-margin} is 0.1, then the scroll margins will never be larger than 2 lines, no matter how big @code{scroll-margin} is. @code{maximum-scroll-margin} itself has a maximum value of 0.5, which allows setting margins large to keep the cursor at the middle line of the window (or two middle lines if the window has an even number of lines). If it's set to a larger value (or any value other than a float between 0.0 and 0.5) then the default value of 0.25 will be used instead. @end defopt @defopt scroll-conservatively This variable controls how scrolling is done automatically when point moves off the screen (or into the scroll margin). If the value is a positive integer @var{n}, then redisplay scrolls the text up to @var{n} lines in either direction, if that will bring point back into proper view. This behavior is called @dfn{conservative scrolling}. Otherwise, scrolling happens in the usual way, under the control of other variables such as @code{scroll-up-aggressively} and @code{scroll-down-aggressively}. The default value is zero, which means that conservative scrolling never happens. @end defopt @defopt scroll-down-aggressively The value of this variable should be either @code{nil} or a fraction @var{f} between 0 and 1. If it is a fraction, that specifies where on the screen to put point when scrolling down. More precisely, when a window scrolls down because point is above the window start, the new start position is chosen to put point @var{f} part of the window height from the top. The larger @var{f}, the more aggressive the scrolling. A value of @code{nil} is equivalent to .5, since its effect is to center point. This variable automatically becomes buffer-local when set in any fashion. @end defopt @defopt scroll-up-aggressively Likewise, for scrolling up. The value, @var{f}, specifies how far point should be placed from the bottom of the window; thus, as with @code{scroll-down-aggressively}, a larger value scrolls more aggressively. @end defopt @defopt scroll-step This variable is an older variant of @code{scroll-conservatively}. The difference is that if its value is @var{n}, that permits scrolling only by precisely @var{n} lines, not a smaller number. This feature does not work with @code{scroll-margin}. The default value is zero. @end defopt @cindex @code{scroll-command} property @defopt scroll-preserve-screen-position If this option is @code{t}, whenever a scrolling command moves point off-window, Emacs tries to adjust point to keep the cursor at its old vertical position in the window, rather than the window edge. If the value is non-@code{nil} and not @code{t}, Emacs adjusts point to keep the cursor at the same vertical position, even if the scrolling command didn't move point off-window. This option affects all scroll commands that have a non-@code{nil} @code{scroll-command} symbol property. @end defopt @defopt next-screen-context-lines The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example, @code{scroll-up} with an argument of @code{nil} scrolls so that this many lines at the bottom of the window appear instead at the top. The default value is @code{2}. @end defopt @defopt scroll-error-top-bottom If this option is @code{nil} (the default), @code{scroll-up-command} and @code{scroll-down-command} simply signal an error when no more scrolling is possible. If the value is @code{t}, these commands instead move point to the beginning or end of the buffer (depending on scrolling direction); only if point is already on that position do they signal an error. @end defopt @deffn Command recenter &optional count redisplay @cindex centering point This function scrolls the text in the selected window so that point is displayed at a specified vertical position within the window. It does not move point with respect to the text. If @var{count} is a non-negative number, that puts the line containing point @var{count} lines down from the top of the window. If @var{count} is a negative number, then it counts upward from the bottom of the window, so that @minus{}1 stands for the last usable line in the window. If @var{count} is @code{nil} (or a non-@code{nil} list), @code{recenter} puts the line containing point in the middle of the window. If @var{count} is @code{nil} and @var{redisplay} is non-@code{nil}, this function may redraw the frame, according to the value of @code{recenter-redisplay}. Thus, omitting the second argument can be used to countermand the effect of @code{recenter-redisplay} being non-@code{nil}. Interactive calls pass non-‘nil’ for @var{redisplay}. When @code{recenter} is called interactively, @var{count} is the raw prefix argument. Thus, typing @kbd{C-u} as the prefix sets the @var{count} to a non-@code{nil} list, while typing @kbd{C-u 4} sets @var{count} to 4, which positions the current line four lines from the top. With an argument of zero, @code{recenter} positions the current line at the top of the window. The command @code{recenter-top-bottom} offers a more convenient way to achieve this. @end deffn @vindex recenter-window-group-function @defun recenter-window-group &optional count This function is like @code{recenter}, except that when the selected window is part of a group of windows (@pxref{Window Group}), @code{recenter-window-group} scrolls the entire group. This condition holds when the buffer local variable @code{recenter-window-group-function} is set to a function. In this case, @code{recenter-window-group} calls the function with the argument @var{count}, then returns its result. The argument @var{count} has the same meaning as in @code{recenter}, but with respect to the entire window group. @end defun @defopt recenter-redisplay If this variable is non-@code{nil}, calling @code{recenter} with a @code{nil} @var{count} argument and non-@code{nil} @var{redisplay} argument redraws the frame. The default value is @code{tty}, which means only redraw the frame if it is a tty frame. @end defopt @deffn Command recenter-top-bottom &optional count This command, which is the default binding for @kbd{C-l}, acts like @code{recenter}, except if called with no argument. In that case, successive calls place point according to the cycling order defined by the variable @code{recenter-positions}. @end deffn @defopt recenter-positions This variable controls how @code{recenter-top-bottom} behaves when called with no argument. The default value is @code{(middle top bottom)}, which means that successive calls of @code{recenter-top-bottom} with no argument cycle between placing point at the middle, top, and bottom of the window. @end defopt @node Vertical Scrolling @section Vertical Fractional Scrolling @cindex vertical fractional scrolling @cindex vertical scroll position @dfn{Vertical fractional scrolling} means shifting text in a window up or down by a specified multiple or fraction of a line. Emacs uses it, for example, on images and screen lines which are taller than the window. Each window has a @dfn{vertical scroll position}, which is a number, never less than zero. It specifies how far to raise the contents of the window when displaying them. Raising the window contents generally makes all or part of some lines disappear off the top, and all or part of some other lines appear at the bottom. The usual value is zero. The vertical scroll position is measured in units of the normal line height, which is the height of the default font. Thus, if the value is .5, that means the window contents will be scrolled up half the normal line height. If it is 3.3, that means the window contents are scrolled up somewhat over three times the normal line height. What fraction of a line the vertical scrolling covers, or how many lines, depends on what the lines contain. A value of .5 could scroll a line whose height is very short off the screen, while a value of 3.3 could scroll just part of the way through a tall line or an image. @defun window-vscroll &optional window pixels-p This function returns the current vertical scroll position of @var{window}. The default for @var{window} is the selected window. If @var{pixels-p} is non-@code{nil}, the return value is measured in pixels, rather than in units of the normal line height. @example @group (window-vscroll) @result{} 0 @end group @end example @end defun @defun set-window-vscroll window lines &optional pixels-p This function sets @var{window}'s vertical scroll position to @var{lines}. If @var{window} is @code{nil}, the selected window is used. The argument @var{lines} should be zero or positive; if not, it is taken as zero. The actual vertical scroll position must always correspond to an integral number of pixels, so the value you specify is rounded accordingly. The return value is the result of this rounding. @example @group (set-window-vscroll (selected-window) 1.2) @result{} 1.13 @end group @end example If @var{pixels-p} is non-@code{nil}, @var{lines} specifies a number of pixels. In this case, the return value is @var{lines}. @end defun @defvar auto-window-vscroll If this variable is non-@code{nil}, the @code{line-move}, @code{scroll-up}, and @code{scroll-down} functions will automatically modify the vertical scroll position to scroll through display rows that are taller than the height of the window, for example in the presence of large images. @end defvar @node Horizontal Scrolling @section Horizontal Scrolling @cindex horizontal scrolling @dfn{Horizontal scrolling} means shifting the image in the window left or right by a specified multiple of the normal character width. Each window has a @dfn{horizontal scroll position}, which is a number, never less than zero. It specifies how far to shift the contents left. Shifting the window contents left generally makes all or part of some characters disappear off the left, and all or part of some other characters appear at the right. The usual value is zero. The horizontal scroll position is measured in units of the normal character width, which is the width of space in the default font. Thus, if the value is 5, that means the window contents are scrolled left by 5 times the normal character width. How many characters actually disappear off to the left depends on their width, and could vary from line to line. Because we read from side to side in the inner loop, and from top to bottom in the outer loop, the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual scrolling involves selection of a portion of text to display, and vertical scrolling moves the window contents contiguously; but horizontal scrolling causes part of @emph{each line} to go off screen. Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge. @vindex auto-hscroll-mode If @code{auto-hscroll-mode} is set, redisplay automatically alters the horizontal scrolling of a window as necessary to ensure that point is always visible. However, you can still set the horizontal scrolling value explicitly. The value you specify serves as a lower bound for automatic scrolling, i.e., automatic scrolling will not scroll a window to a column less than the specified one. The default value of @code{auto-hscroll-mode} is @code{t}; setting it to @code{current-line} activates a variant of automatic horizontal scrolling whereby only the line showing the cursor is horizontally scrolled to make point visible, the rest of the window is left either unscrolled, or at the minimum scroll amount set by @code{scroll-left} and @code{scroll-right}, see below. @deffn Command scroll-left &optional count set-minimum This function scrolls the selected window @var{count} columns to the left (or to the right if @var{count} is negative). The default for @var{count} is the window width, minus 2. The return value is the total amount of leftward horizontal scrolling in effect after the change---just like the value returned by @code{window-hscroll} (below). Note that text in paragraphs whose base direction is right-to-left (@pxref{Bidirectional Display}) moves in the opposite direction: e.g., it moves to the right when @code{scroll-left} is invoked with a positive value of @var{count}. Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect. If @var{set-minimum} is non-@code{nil}, the new scroll amount becomes the lower bound for automatic scrolling; that is, automatic scrolling will not scroll a window to a column less than the value returned by this function. Interactive calls pass non-@code{nil} for @var{set-minimum}. @end deffn @deffn Command scroll-right &optional count set-minimum This function scrolls the selected window @var{count} columns to the right (or to the left if @var{count} is negative). The default for @var{count} is the window width, minus 2. Aside from the direction of scrolling, this works just like @code{scroll-left}. @end deffn @defun window-hscroll &optional window This function returns the total leftward horizontal scrolling of @var{window}---the number of columns by which the text in @var{window} is scrolled left past the left margin. (In right-to-left paragraphs, the value is the total amount of the rightward scrolling instead.) The default for @var{window} is the selected window. The return value is never negative. It is zero when no horizontal scrolling has been done in @var{window} (which is usually the case). @example @group (window-hscroll) @result{} 0 @end group @group (scroll-left 5) @result{} 5 @end group @group (window-hscroll) @result{} 5 @end group @end example @end defun @defun set-window-hscroll window columns This function sets horizontal scrolling of @var{window}. The value of @var{columns} specifies the amount of scrolling, in terms of columns from the left margin (right margin in right-to-left paragraphs). The argument @var{columns} should be zero or positive; if not, it is taken as zero. Fractional values of @var{columns} are not supported at present. Note that @code{set-window-hscroll} may appear not to work if you test it by evaluating a call with @kbd{M-:} in a simple way. What happens is that the function sets the horizontal scroll value and returns, but then redisplay adjusts the horizontal scrolling to make point visible, and this overrides what the function did. You can observe the function's effect if you call it while point is sufficiently far from the left margin that it will remain visible. The value returned is @var{columns}. @example @group (set-window-hscroll (selected-window) 10) @result{} 10 @end group @end example @end defun Here is how you can determine whether a given position @var{position} is off the screen due to horizontal scrolling: @c FIXME: Maybe hscroll-on-screen-p is a better name? @example @group (defun hscroll-on-screen (window position) (save-excursion (goto-char position) (and (>= (- (current-column) (window-hscroll window)) 0) (< (- (current-column) (window-hscroll window)) (window-width window))))) @end group @end example @node Coordinates and Windows @section Coordinates and Windows @cindex frame-relative coordinate @cindex coordinate, relative to frame @cindex window position This section describes functions that report positions of and within a window. Most of these functions report positions relative to an origin at the native position of the window's frame (@pxref{Frame Geometry}). Some functions report positions relative to the origin of the display of the window's frame. In any case, the origin has the coordinates (0, 0) and X and Y coordinates increase rightward and downward respectively. For the following functions, X and Y coordinates are reported in integer character units, i.e., numbers of lines and columns respectively. On a graphical display, each ``line'' and ``column'' corresponds to the height and width of the default character specified by the frame's default font (@pxref{Frame Font}). @defun window-edges &optional window body absolute pixelwise This function returns a list of the edge coordinates of @var{window}. If @var{window} is omitted or @code{nil}, it defaults to the selected window. The return value has the form @code{(@var{left} @var{top} @var{right} @var{bottom})}. These list elements are, respectively, the X coordinate of the leftmost column occupied by the window, the Y coordinate of the topmost row, the X coordinate one column to the right of the rightmost column, and the Y coordinate one row down from the bottommost row. Note that these are the actual outer edges of the window, including any header line, mode line, scroll bar, fringes, window divider and display margins. On a text terminal, if the window has a neighbor on its right, its right edge includes the separator line between the window and its neighbor. If the optional argument @var{body} is @code{nil}, this means to return the edges corresponding to the total size of @var{window}. @var{body} non-@code{nil} means to return the edges of @var{window}'s body (aka text area). If @var{body} is non-@code{nil}, @var{window} must specify a live window. If the optional argument @var{absolute} is @code{nil}, this means to return edges relative to the native position of @var{window}'s frame. @var{absolute} non-@code{nil} means to return coordinates relative to the origin (0, 0) of @var{window}'s display. On non-graphical systems this argument has no effect. If the optional argument @var{pixelwise} is @code{nil}, this means to return the coordinates in terms of the default character width and height of @var{window}'s frame (@pxref{Frame Font}), rounded if necessary. @var{pixelwise} non-@code{nil} means to return the coordinates in pixels. Note that the pixel specified by @var{right} and @var{bottom} is immediately outside of these edges. If @var{absolute} is non-@code{nil}, @var{pixelwise} is implicitly non-@code{nil} too. @end defun @defun window-body-edges &optional window This function returns the edges of @var{window}'s body (@pxref{Window Sizes}). Calling @code{(window-body-edges window)} is equivalent to calling @code{(window-edges window t)}, see above. @end defun @comment The following two functions are confusing and hardly used. @ignore @defun window-left-column &optional window This function returns the leftmost column of @var{window}. This value equals the @var{left} entry in the list returned by @code{(window-edges window)} minus the number of columns occupied by the internal border of @var{window}'s frame. @end defun @defun window-top-line &optional window This function returns the topmost row of @var{window}. This value is equal to the @var{top} entry in the list returned by @code{(window-edges window)} minus the number of lines occupied by the internal border of @var{window}'s frame. @end defun @end ignore The following functions can be used to relate a set of frame-relative coordinates to a window: @defun window-at x y &optional frame This function returns the live window at the coordinates @var{x} and @var{y} given in default character sizes (@pxref{Frame Font}) relative to the native position of @var{frame} (@pxref{Frame Geometry}). If there is no window at that position, the return value is @code{nil}. If @var{frame} is omitted or @code{nil}, it defaults to the selected frame. @end defun @defun coordinates-in-window-p coordinates window This function checks whether a window @var{window} occupies the frame relative coordinates @var{coordinates}, and if so, which part of the window that is. @var{window} should be a live window. @var{coordinates} should be a cons cell of the form @code{(@var{x} . @var{y})}, where @var{x} and @var{y} are given in default character sizes (@pxref{Frame Font}) relative to the native position of @var{window}'s frame (@pxref{Frame Geometry}). If there is no window at the specified position, the return value is @code{nil} . Otherwise, the return value is one of the following: @table @code @item (@var{relx} . @var{rely}) The coordinates are inside @var{window}. The numbers @var{relx} and @var{rely} are the equivalent window-relative coordinates for the specified position, counting from 0 at the top left corner of the window. @item mode-line The coordinates are in the mode line of @var{window}. @item header-line The coordinates are in the header line of @var{window}. @item tab-line The coordinates are in the tab line of @var{window}. @item right-divider The coordinates are in the divider separating @var{window} from a window on the right. @item bottom-divider The coordinates are in the divider separating @var{window} from a window beneath. @item vertical-line The coordinates are in the vertical line between @var{window} and its neighbor to the right. This value occurs only if the window doesn't have a scroll bar; positions in a scroll bar are considered outside the window for these purposes. @item left-fringe @itemx right-fringe The coordinates are in the left or right fringe of the window. @item left-margin @itemx right-margin The coordinates are in the left or right margin of the window. @item nil The coordinates are not in any part of @var{window}. @end table The function @code{coordinates-in-window-p} does not require a frame as argument because it always uses the frame that @var{window} is on. @end defun The following functions return window positions in pixels, rather than character units. Though mostly useful on graphical displays, they can also be called on text terminals, where the screen area of each text character is taken to be one pixel. @defun window-pixel-edges &optional window This function returns a list of pixel coordinates for the edges of @var{window}. Calling @code{(window-pixel-edges window)} is equivalent to calling @code{(window-edges window nil nil t)}, see above. @end defun @comment The following two functions are confusing and hardly used. @ignore @defun window-pixel-left &optional window This function returns the left pixel edge of window @var{window}. This value equals the @var{left} entry in the list returned by @code{(window-pixel-edges window)} minus the number of pixels occupied by the internal border of @var{window}'s frame. @var{window} must be a valid window and defaults to the selected one. @end defun @defun window-pixel-top &optional window This function returns the top pixel edge of window @var{window}. This value is equal to the @var{top} entry in the list returned by @code{(window-pixel-edges window)} minus the number of pixels occupied by the internal border of @var{window}'s frame. @var{window} must be a valid window and defaults to the selected one. @end defun @end ignore @defun window-body-pixel-edges &optional window This function returns the pixel edges of @var{window}'s body. Calling @code{(window-body-pixel-edges window)} is equivalent to calling @code{(window-edges window t nil t)}, see above. @end defun The following functions return window positions in pixels, relative to the origin of the display screen rather than that of the frame: @defun window-absolute-pixel-edges &optional window This function returns the pixel coordinates of @var{window} relative to an origin at (0, 0) of the display of @var{window}'s frame. Calling @code{(window-absolute-pixel-edges)} is equivalent to calling @code{(window-edges window nil t t)}, see above. @end defun @defun window-absolute-body-pixel-edges &optional window This function returns the pixel coordinates of @var{window}'s body relative to an origin at (0, 0) of the display of @var{window}'s frame. Calling @code{(window-absolute-body-pixel-edges window)} is equivalent to calling @code{(window-edges window t t t)}, see above. Combined with @code{set-mouse-absolute-pixel-position}, this function can be used to move the mouse pointer to an arbitrary buffer position visible in some window: @example @group (let ((edges (window-absolute-body-pixel-edges)) (position (pos-visible-in-window-p nil nil t))) (set-mouse-absolute-pixel-position (+ (nth 0 edges) (nth 0 position)) (+ (nth 1 edges) (nth 1 position)))) @end group @end example On a graphical terminal this form ``warps'' the mouse cursor to the upper left corner of the glyph at the selected window's point. A position calculated this way can be also used to show a tooltip window there. @end defun The following function returns the screen coordinates of a buffer position visible in a window: @defun window-absolute-pixel-position &optional position window If the buffer position @var{position} is visible in window @var{window}, this function returns the display coordinates of the upper/left corner of the glyph at @var{position}. The return value is a cons of the X- and Y-coordinates of that corner, relative to an origin at (0, 0) of @var{window}'s display. It returns @code{nil} if @var{position} is not visible in @var{window}. @var{window} must be a live window and defaults to the selected window. @var{position} defaults to the value of @code{window-point} of @var{window}. This means that in order to move the mouse pointer to the position of point in the selected window, it's sufficient to write: @example @group (let ((position (window-absolute-pixel-position))) (set-mouse-absolute-pixel-position (car position) (cdr position))) @end group @end example @end defun The following function returns the largest rectangle that can be inscribed in a window without covering text displayed in that window. @defun window-largest-empty-rectangle &optional window count min-width min-height positions left This function calculates the dimensions of the largest empty rectangle that can be inscribed in the specified @var{window}'s text area. @var{window} must be a live window and defaults to the selected one. The return value is a triple of the width and the start and end y-coordinates of the largest rectangle that can be inscribed into the empty space (space not displaying any text) of the text area of @var{window}. No x-coordinates are returned by this function---any such rectangle is assumed to end at the right edge of @var{window}'s text area. If no empty space can be found, the return value is @code{nil}. The optional argument @var{count}, if non-@code{nil}, specifies a maximum number of rectangles to return. This means that the return value is a list of triples specifying rectangles with the largest rectangle first. @var{count} can be also a cons cell whose car specifies the number of rectangles to return and whose @sc{cdr}, if non-@code{nil}, states that all rectangles returned must be disjoint. The optional arguments @var{min-width} and @var{min-height}, if non-@code{nil}, specify the minimum width and height of any rectangle returned. The optional argument @var{positions}, if non-@code{nil}, is a cons cell whose @sc{car} specifies the uppermost and whose @sc{cdr} specifies the lowermost pixel position that must be covered by any rectangle returned. These positions measure from the start of the text area of @var{window}. The optional argument @var{left}, if non-@code{nil}, means to return values suitable for buffers displaying right to left text. In that case, any rectangle returned is assumed to start at the left edge of @var{window}'s text area. Note that this function has to retrieve the dimensions of each line of @var{window}'s glyph matrix via @code{window-lines-pixel-dimensions} (@pxref{Size of Displayed Text}). Hence, this function may also return @code{nil} when the current glyph matrix of @var{window} is not up-to-date. @end defun @node Mouse Window Auto-selection @section Mouse Window Auto-selection @cindex window auto-selection @cindex auto-selection of window The following option allows to automatically select the window under the mouse pointer. This accomplishes a policy similar to that of window managers that give focus to a frame (and thus trigger its subsequent selection) whenever the mouse pointer enters its window-system window (@pxref{Input Focus}). @defopt mouse-autoselect-window If this variable is non-@code{nil}, Emacs will try to automatically select the window under the mouse pointer. The following values are meaningful: @table @asis @item A positive number This specifies a delay in seconds after which auto-selection triggers. The window under the mouse pointer is selected after the mouse has remained in it for the entire duration of the delay. @item A negative number A negative number has a similar effect as a positive number, but selects the window under the mouse pointer only after the mouse pointer has remained in it for the entire duration of the absolute value of that number and in addition has stopped moving. @item Other value Any other non-@code{nil} value means to select a window instantaneously as soon as the mouse pointer enters it. @end table In either case, the mouse pointer must enter the text area of a window in order to trigger its selection. Dragging the scroll bar slider or the mode line of a window conceptually should not cause its auto-selection. Mouse auto-selection selects the minibuffer window only if it is active, and never deselects the active minibuffer window. @end defopt Mouse auto-selection can be used to emulate a focus follows mouse policy for child frames (@pxref{Child Frames}) which usually are not tracked by the window manager. This requires to set the value of @code{focus-follows-mouse} (@pxref{Input Focus}) to a non-@code{nil} value. If the value of @code{focus-follows-mouse} is @code{auto-raise}, entering a child frame with the mouse will raise it automatically above all other child frames of that frame's parent frame. @node Window Configurations @section Window Configurations @cindex window configurations @cindex saving window information A @dfn{window configuration} records the entire layout of one frame---all windows, their sizes, which buffers they contain, how those buffers are scrolled, and their value of point; also their fringes, margins, and scroll bar settings. It also includes the value of @code{minibuffer-scroll-window}. As a special exception, the window configuration does not record the value of point in the selected window for the current buffer. You can bring back an entire frame layout by restoring a previously saved window configuration. If you want to record the layout of all frames instead of just one, use a frame configuration instead of a window configuration. @xref{Frame Configurations}. @defun current-window-configuration &optional frame This function returns a new object representing @var{frame}'s current window configuration. The default for @var{frame} is the selected frame. The variable @code{window-persistent-parameters} specifies which window parameters (if any) are saved by this function. @xref{Window Parameters}. @end defun @defun set-window-configuration configuration &optional dont-set-frame This function restores the configuration of windows and buffers as specified by @var{configuration}, for the frame that @var{configuration} was created for, regardless of whether that frame is selected or not. The argument @var{configuration} must be a value that was previously returned by @code{current-window-configuration} for that frame. Normally the function also selects the frame which is recorded in the configuration, but if @var{dont-set-frame} is non-@code{nil}, it leaves selected the frame which was current at the start of the function. If the frame from which @var{configuration} was saved is dead, all this function does is to restore the value of the variable @code{minibuffer-scroll-window} and to adjust the value returned by @code{minibuffer-selected-window}. In this case, the function returns @code{nil}. Otherwise, it returns @code{t}. If the buffer of a window of @var{configuration} has been killed since @var{configuration} was made, that window is, as a rule, removed from the restored configuration. However, if that window is the last window remaining in the restored configuration, another live buffer is shown in it. Here is a way of using this function to get the same effect as @code{save-window-excursion}: @example @group (let ((config (current-window-configuration))) (unwind-protect (progn (split-window-below nil) @dots{}) (set-window-configuration config))) @end group @end example @end defun @defmac save-window-excursion forms@dots{} This macro records the window configuration of the selected frame, executes @var{forms} in sequence, then restores the earlier window configuration. The return value is the value of the final form in @var{forms}. Most Lisp code should not use this macro; @code{save-selected-window} is typically sufficient. In particular, this macro cannot reliably prevent the code in @var{forms} from opening new windows, because new windows might be opened in other frames (@pxref{Choosing Window}), and @code{save-window-excursion} only saves and restores the window configuration on the current frame. @end defmac @defun window-configuration-p object This function returns @code{t} if @var{object} is a window configuration. @end defun @defun compare-window-configurations config1 config2 This function compares two window configurations as regards the structure of windows, but ignores the values of point and the saved scrolling positions---it can return @code{t} even if those aspects differ. @end defun @defun window-configuration-frame config This function returns the frame for which the window configuration @var{config} was made. @end defun Other primitives to look inside of window configurations would make sense, but are not implemented because we did not need them. See the file @file{winner.el} for some more operations on windows configurations. The objects returned by @code{current-window-configuration} die together with the Emacs process. In order to store a window configuration on disk and read it back in another Emacs session, you can use the functions described next. These functions are also useful to clone the state of a frame into an arbitrary live window (@code{set-window-configuration} effectively clones the windows of a frame into the root window of that very frame only). @cindex window state @defun window-state-get &optional window writable This function returns the state of @var{window} as a Lisp object. The argument @var{window} must be a valid window and defaults to the root window of the selected frame. If the optional argument @var{writable} is non-@code{nil}, this means to not use markers for sampling positions like @code{window-point} or @code{window-start}. This argument should be non-@code{nil} when the state will be written to disk and read back in another session. Together, the argument @var{writable} and the variable @code{window-persistent-parameters} specify which window parameters are saved by this function. @xref{Window Parameters}. @end defun The value returned by @code{window-state-get} can be used in the same session to make a clone of a window in another window. It can be also written to disk and read back in another session. In either case, use the following function to restore the state of the window. @defun window-state-put state &optional window ignore This function puts the window state @var{state} into @var{window}. The argument @var{state} should be the state of a window returned by an earlier invocation of @code{window-state-get}, see above. The optional argument @var{window} can be either a live window or an internal window (@pxref{Windows and Frames}). If @var{window} is not a live window, it is replaced by a new live window created on the same frame before putting @var{state} into it. If @var{window} is @code{nil}, it puts the window state into a new window. If the optional argument @var{ignore} is non-@code{nil}, it means to ignore minimum window sizes and fixed-size restrictions. If @var{ignore} is @code{safe}, this means windows can get as small as one line and/or two columns. @end defun The functions @code{window-state-get} and @code{window-state-put} also allow to exchange the contents of two live windows. The following function does precisely that: @deffn Command window-swap-states &optional window-1 window-2 size This command swaps the states of the two live windows @var{window-1} and @var{window-2}. @var{window-1} must specify a live window and defaults to the selected one. @var{window-2} must specify a live window and defaults to the window following @var{window-1} in the cyclic ordering of windows, excluding minibuffer windows and including live windows on all visible frames. Optional argument @var{size} non-@code{nil} means to try swapping the sizes of @var{window-1} and @var{window-2} as well. A value of @code{height} means to swap heights only, a value of @code{width} means to swap widths only, while @code{t} means to swap both widths and heights, if possible. Frames are not resized by this function. @end deffn @node Window Parameters @section Window Parameters @cindex window parameters This section describes the window parameters that can be used to associate additional information with windows. @defun window-parameter window parameter This function returns @var{window}'s value for @var{parameter}. The default for @var{window} is the selected window. If @var{window} has no setting for @var{parameter}, this function returns @code{nil}. @end defun @defun window-parameters &optional window This function returns all parameters of @var{window} and their values. The default for @var{window} is the selected window. The return value is either @code{nil}, or an association list whose elements have the form @code{(@var{parameter} . @var{value})}. @end defun @defun set-window-parameter window parameter value This function sets @var{window}'s value of @var{parameter} to @var{value} and returns @var{value}. The default for @var{window} is the selected window. @end defun By default, the functions that save and restore window configurations or the states of windows (@pxref{Window Configurations}) do not care about window parameters. This means that when you change the value of a parameter within the body of a @code{save-window-excursion}, the previous value is not restored when that macro exits. It also means that when you restore via @code{window-state-put} a window state saved earlier by @code{window-state-get}, all cloned windows have their parameters reset to @code{nil}. The following variable allows you to override the standard behavior: @cindex persistent window parameters @defvar window-persistent-parameters This variable is an alist specifying which parameters get saved by @code{current-window-configuration} and @code{window-state-get}, and subsequently restored by @code{set-window-configuration} and @code{window-state-put}. @xref{Window Configurations}. The @sc{car} of each entry of this alist is a symbol specifying the parameter. The @sc{cdr} should be one of the following: @table @asis @item @code{nil} This value means the parameter is saved neither by @code{window-state-get} nor by @code{current-window-configuration}. @item @code{t} This value specifies that the parameter is saved by @code{current-window-configuration} and (provided its @var{writable} argument is @code{nil}) by @code{window-state-get}. @item @code{writable} This means that the parameter is saved unconditionally by both @code{current-window-configuration} and @code{window-state-get}. This value should not be used for parameters whose values do not have a read syntax. Otherwise, invoking @code{window-state-put} in another session may fail with an @code{invalid-read-syntax} error. @end table @end defvar Some functions (notably @code{delete-window}, @code{delete-other-windows} and @code{split-window}), may behave specially when the window specified by their @var{window} argument has a parameter whose name is equal to the function's name. You can override such special behavior by binding the following variable to a non-@code{nil} value: @defvar ignore-window-parameters If this variable is non-@code{nil}, some standard functions do not process window parameters. The functions currently affected by this are @code{split-window}, @code{delete-window}, @code{delete-other-windows}, and @code{other-window}. An application can bind this variable to a non-@code{nil} value around calls to these functions. If it does so, the application is fully responsible for correctly assigning the parameters of all involved windows when exiting that function. @end defvar The following parameters are currently used by the window management code: @table @code @item delete-window @vindex delete-window@r{, a window parameter} This parameter affects the execution of @code{delete-window} (@pxref{Deleting Windows}). @item delete-other-windows @vindex delete-other-windows@r{, a window parameter} This parameter affects the execution of @code{delete-other-windows} (@pxref{Deleting Windows}). @item no-delete-other-windows @vindex no-delete-other-windows@r{, a window parameter} This parameter marks the window as not deletable by @code{delete-other-windows} (@pxref{Deleting Windows}). @item split-window @vindex split-window@r{, a window parameter} This parameter affects the execution of @code{split-window} (@pxref{Splitting Windows}). @item other-window @vindex other-window@r{, a window parameter} This parameter affects the execution of @code{other-window} (@pxref{Cyclic Window Ordering}). @item no-other-window @vindex no-other-window@r{, a window parameter} This parameter marks the window as not selectable by @code{other-window} (@pxref{Cyclic Window Ordering}). @item clone-of @vindex clone-of@r{, a window parameter} This parameter specifies the window that this one has been cloned from. It is installed by @code{window-state-get} (@pxref{Window Configurations}). @item window-preserved-size @vindex window-preserved-size@r{, a window parameter} This parameter specifies a buffer, a direction where @code{nil} means vertical and @code{t} horizontal, and a size in pixels. If this window displays the specified buffer and its size in the indicated direction equals the size specified by this parameter, then Emacs will try to preserve the size of this window in the indicated direction. This parameter is installed and updated by the function @code{window-preserve-size} (@pxref{Preserving Window Sizes}). @item quit-restore @vindex quit-restore@r{, a window parameter} This parameter is installed by the buffer display functions (@pxref{Choosing Window}) and consulted by @code{quit-restore-window} (@pxref{Quitting Windows}). It is a list of four elements, see the description of @code{quit-restore-window} in @ref{Quitting Windows} for details. @item window-side @itemx window-slot @vindex window-side@r{, a window parameter} @vindex window-slot@r{, a window parameter} These parameters are used internally for implementing side windows (@pxref{Side Windows}). @item window-atom @vindex window-atom@r{, a window parameter} This parameter is used internally for implementing atomic windows, see @ref{Atomic Windows}. @item mode-line-format @vindex mode-line-format@r{, a window parameter} This parameter replaces the value of the buffer-local variable @code{mode-line-format} (@pxref{Mode Line Basics}) of this window's buffer whenever this window is displayed. The symbol @code{none} means to suppress display of a mode line for this window. Display and contents of the mode line on other windows showing this buffer are not affected. @item header-line-format @vindex header-line-format@r{, a window parameter} This parameter replaces the value of the buffer-local variable @code{header-line-format} (@pxref{Mode Line Basics}) of this window's buffer whenever this window is displayed. The symbol @code{none} means to suppress display of a header line for this window. Display and contents of the header line on other windows showing this buffer are not affected. @item tab-line-format @vindex tab-line-format@r{, a window parameter} This parameter replaces the value of the buffer-local variable @code{tab-line-format} (@pxref{Mode Line Basics}) of this window's buffer whenever this window is displayed. The symbol @code{none} means to suppress display of a tab line for this window. Display and contents of the tab line on other windows showing this buffer are not affected. @item min-margins @vindex min-margins@r{, a window parameter} The value of this parameter is a cons cell whose @sc{car} and @sc{cdr}, if non-@code{nil}, specify the minimum values (in columns) for the left and right margin of this window (@pxref{Display Margins}. When present, Emacs will use these values instead of the actual margin widths for determining whether a window can be split or shrunk horizontally. Emacs never auto-adjusts the margins of any window after splitting or resizing it. It is the sole responsibility of any application setting this parameter to adjust the margins of this window as well as those of any new window that inherits this window's margins due to a split. Both @code{window-configuration-change-hook} and @code{window-size-change-functions} (@pxref{Window Hooks}) should be employed for this purpose. This parameter was introduced in Emacs version 25.1 to support applications that use large margins to center buffer text within a window and should be used, with due care, exclusively by those applications. It might be replaced by an improved solution in future versions of Emacs. @end table @node Window Hooks @section Hooks for Window Scrolling and Changes @cindex hooks for window operations This section describes how Lisp programs can take action after a window has been scrolled or other window modifications occurred. We first consider the case where a window shows a different part of its buffer. @defvar window-scroll-functions This variable holds a list of functions that Emacs should call before redisplaying a window with scrolling. Displaying a different buffer in a window and making a new window also call these functions. This variable is not a normal hook, because each function is called with two arguments: the window, and its new display-start position. At the time of the call, the display-start position of the argument window is already set to its new value, and the buffer to be displayed in the window is set as the current buffer. These functions must take care when using @code{window-end} (@pxref{Window Start and End}); if you need an up-to-date value, you must use the @var{update} argument to ensure you get it. @strong{Warning:} don't use this feature to alter the way the window is scrolled. It's not designed for that, and such use probably won't work. @end defvar In addition, you can use @code{jit-lock-register} to register a Font Lock fontification function, which will be called whenever parts of a buffer are (re)fontified because a window was scrolled or its size changed. @xref{Other Font Lock Variables}. @cindex window change functions The remainder of this section covers six hooks that are called during redisplay provided a significant, non-scrolling change of a window has been detected. For simplicity, these hooks and the functions they call will be collectively referred to as @dfn{window change functions}. @cindex window buffer change The first of these hooks is run after a @dfn{window buffer change} is detected, which means that a window was created, deleted or assigned another buffer. @defvar window-buffer-change-functions This variable specifies functions called during redisplay when window buffers have changed. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been created or assigned that buffer since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if at least one window on that frame has been added, deleted or assigned another buffer since the last time window change functions were run. In this case the frame is passed as argument. @end defvar @cindex window size change The second of these hooks is run when a @dfn{window size change} has been detected which means that a window was created, assigned another buffer, or changed its total size or that of its text area. @defvar window-size-change-functions This variable specifies functions called during redisplay when a window size change occurred. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been added or assigned another buffer or changed its total or body size since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if at least one window on that frame has been added or assigned another buffer or changed its total or body size since the last time window change functions were run. In this case the frame is passed as argument. @end defvar @cindex window selection change The third of these hooks is run when a @dfn{window selection change} has selected another window since the last redisplay. @defvar window-selection-change-functions This variable specifies functions called during redisplay when the selected window or a frame's selected window has changed. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been selected or deselected (among all windows or among all windows on its frame) since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if that frame has been selected or deselected or the frame's selected window has changed since the last time window change functions were run. In this case the frame is passed as argument. @end defvar @cindex window state change The fourth of these hooks is run when a @dfn{window state change} has been detected, which means that at least one of the three preceding window changes has occurred. @defvar window-state-change-functions This variable specifies functions called during redisplay when a window buffer or size change occurred or the selected window or a frame's selected window has changed. The value should be a list of functions that take one argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if that window has been added or assigned another buffer, changed its total or body size or has been selected or deselected (among all windows or among all windows on its frame) since the last time window change functions were run. In this case the window is passed as argument. Functions specified by the default value are called for a frame if at least one window on that frame has been added, deleted or assigned another buffer, changed its total or body size or that frame has been selected or deselected or the frame's selected window has changed since the last time window change functions were run. In this case the frame is passed as argument. Functions specified by the default value are also run for a frame when that frame's window state change flag (see below) has been set since last redisplay. @end defvar @cindex window configuration change The fifth of these hooks is run when a @dfn{window configuration change} has been detected which means that either the buffer or the size of a window changed. It differs from the four preceding hooks in the way it is run. @defvar window-configuration-change-hook This variable specifies functions called during redisplay when either the buffer or the size of a window has changed. The value should be a list of functions that take no argument. Functions specified buffer-locally are called for any window showing the corresponding buffer if at least one window on that frame has been added, deleted or assigned another buffer or changed its total or body size since the last time window change functions were run. Each call is performed with the window showing the buffer temporarily selected and its buffer current. Functions specified by the default value are called for each frame if at least one window on that frame has been added, deleted or assigned another buffer or changed its total or body size since the last time window change functions were run. Each call is performed with the frame temporarily selected and the selected window's buffer current. @end defvar Finally, Emacs runs a normal hook that generalizes the behavior of @code{window-state-change-functions}. @defvar window-state-change-hook The default value of this variable specifies functions called during redisplay when a window state change has been detected or the window state change flag has been set on at least one frame. The value should be a list of functions that take no argument. Applications should put a function on this hook only if they want to react to changes that happened on (or have been signaled for) two or more frames since last redisplay. In every other case, putting the function on @code{window-state-change-functions} should be preferred. @end defvar Window change functions are called during redisplay for each frame as follows: First, any buffer-local window buffer change function, window size change function, selected window change and window state change functions are called in this order. Next, the default values for these functions are called in the same order. Then any buffer-local window configuration change functions are called followed by functions specified by the default value of those functions. Finally, functions on @code{window-state-change-hook} are run. Window change functions are run for a specific frame only if a corresponding change was registered for that frame earlier. Such changes include the creation or deletion of a window or the assignment of another buffer or size to a window. Note that even when such a change has been registered, this does not mean that any of the hooks described above is run. If, for example, a change was registered within the scope of a window excursion (@pxref{Window Configurations}), this will trigger a call of window change functions only if that excursion still persists at the time change functions are run. If it is exited earlier, hooks will be run only if registered by a change outside the scope of that excursion. @cindex window state change flag The @dfn{window state change flag} of a frame, if set, will cause the default values of @code{window-state-change-functions} (for that frame) and @code{window-state-change-hook} to be run during next redisplay regardless of whether a window state change actually occurred for that frame or not. After running any functions on these hooks, the flag is reset for each frame. Applications can set that flag and inspect its value using the following functions. @defun set-frame-window-state-change &optional frame arg This function sets @var{frame}'s window state change flag if @var{arg} is non-@code{nil} and resets it otherwise. @var{frame} must be a live frame and defaults to the selected one. @end defun @defun frame-window-state-change &optional frame This functions returns @code{t} if @var{frame}'s window state change flag is set and @code{nil} otherwise. @var{frame} must be a live frame and defaults to the selected one. @end defun While window change functions are run, the functions described next can be called to get more insight into what has changed for a specific window or frame since the last redisplay. All these functions take a live window as single, optional argument, defaulting to the selected window. @defun window-old-buffer &optional window This function returns the buffer shown in @var{window} at the last time window change functions were run for @var{window}'s frame. If it returns @code{nil}, @var{window} has been created after that. If it returns @code{t}, @var{window} was not shown at that time but has been restored from a previously saved window configuration afterwards. Otherwise, the return value is the buffer shown by @code{window} at that time. @end defun @defun window-old-pixel-width &optional window This function returns the total pixel width of @var{window} the last time window change functions found @code{window} live on its frame. It is zero if @code{window} was created after that. @end defun @defun window-old-pixel-height &optional window This function returns the total pixel height of @var{window} the last time window change functions found @code{window} live on its frame. It is zero if @code{window} was created after that. @end defun @defun window-old-body-pixel-width &optional window This function returns the pixel width of @var{window}'s text area the last time window change functions found @code{window} live on its frame. It is zero if @code{window} was created after that. @end defun @defun window-old-body-pixel-height &optional window This function returns the pixel height of @var{window}'s text area the last time window change functions found @code{window} live on its frame. It is zero if @code{window} was created after that. @end defun In order to find out which window or frame was selected the last time window change functions were run, the following functions can be used: @defun frame-old-selected-window &optional frame This function returns the selected window of @var{frame} at the last time window change functions were run. If omitted or @code{nil} @var{frame} defaults to the selected frame. @end defun @defun old-selected-window This function returns the selected window at the last time window change functions were run. @end defun @defun old-selected-frame This function returns the selected frame at the last time window change functions were run. @end defun Note that window change functions provide no information about which windows have been deleted since the last time they were run. If necessary, applications should remember any window showing a specific buffer in a local variable of that buffer and update it in a function run by the default values of any of the hooks that are run when a window buffer change was detected. The following caveats should be considered when adding a function to window change functions: @itemize @bullet @item Some operations will not trigger a call of window change functions. These include showing another buffer in a minibuffer window or any change of a tooltip window. @item Window change functions should not create or delete windows or change the buffer, size or selection status of any window because there is no guarantee that the information about such a change will be propagated to other window change functions. If at all, any such change should be executed only by the last function listed by the default value of @code{window-state-change-hook}. @item Macros like @code{save-window-excursion}, @code{with-selected-window} or @code{with-current-buffer} can be used when running window change functions. @item Running window change functions does not save and restore match data. Unless running @code{window-configuration-change-hook} it does not save or restore the selected window or frame or the current buffer either. @item Any redisplay triggering the run of window change functions may be aborted. If the abort occurs before window change functions have run to their completion, they will be run again with the previous values, that is, as if redisplay had not been performed. If aborted later, they will be run with the new values, that is, as if redisplay had been actually performed. @end itemize