Add distinct controls for child frames' borders (Bug#45620)

The background of the 'child-frame-border' face instead of the
'internal-border' face now controls the color of child frames'
borders.

The 'child-frame-border-width' frame parameter is now used for the
width of child frames' borders instead of internal-border-width',
though we still fall back on using the latter if the former is not
set.

* doc/lispref/frames.texi (Frame Layout): Mention
'child-frame-border' and 'child-frame-border-width'.
(Layout Parameters): Mention 'child-frame-border-width'.
* etc/NEWS: Mention new face 'child-frame-border' and frame
parameter 'child-frame-border-width'.
* lisp/faces.el (child-frame-border): New face.
* src/dispextern.h (enum face_id): Add CHILD_FRAME_BORDER_FACE_ID.
* src/frame.c (Fframe_child_frame_border_width): New function.
(gui_report_frame_params): Add entry for Qchild_frame_border_width.
* src/frame.h (struct frame): New slot child_frame_border_width.
(FRAME_CHILD_FRAME_BORDER_WIDTH): New inlined function.
* src/nsfns.m (ns_set_child_frame_border_width): New function.
(Fx_create_frame): Handle Qchild_frame_border_width parameter.
(ns_frame_parm_handlers): Add ns_set_child_frame_border_width.
* src/nsterm.m (ns_clear_under_internal_border): Handle
CHILD_FRAME_BORDER_FACE_ID.
* src/w32fns.c (w32_clear_under_internal_border): Handle
CHILD_FRAME_BORDER_FACE_ID.
(w32_set_internal_border_width): New function.
(Fx_create_frame): Handle Qchild_frame_border_width parameter.
(w32_frame_parm_handlers): Add w32_set_child_frame_border_width.
* src/xfaces.c (lookup_basic_face, realize_basic_faces): Handle
CHILD_FRAME_BORDER_FACE_ID.
* src/xfns.c (x_set_child_frame_border_width): New function.
(Fx_create_frame): Handle Qchild_frame_border_width parameter.
(x_frame_parm_handlers): Add x_set_child_frame_border_width.
* src/xterm.c (x_clear_under_internal_border)
(x_after_update_window_line): Handle CHILD_FRAME_BORDER_FACE_ID.

1 files changed, 22 insertions, 2 deletions

diff --git a/src/frame.h b/src/frame.h
index 8cf41dc0046..7b3bf20a241 100644
--- a/src/frame.h
+++ b/src/frame.h
@@ -534,6 +534,10 @@ struct frame
   /* Border width of the frame window as known by the (X) window system.  */
   int border_width;
 
+  /* Width of child frames' internal border. Acts as
+     internal_border_width for child frames.  */
+  int child_frame_border_width;
+
   /* Width of the internal border.  This is a line of background color
      just inside the window's border.  When the frame is selected,
      a highlighting is displayed inside the internal border.  */
@@ -1432,11 +1436,27 @@ FRAME_TOTAL_FRINGE_WIDTH (struct frame *f)
   return FRAME_LEFT_FRINGE_WIDTH (f) + FRAME_RIGHT_FRINGE_WIDTH (f);
 }
 
-/* Pixel-width of internal border lines.  */
+INLINE int
+FRAME_CHILD_FRAME_BORDER_WIDTH (struct frame *f)
+{
+  return frame_dimension (f->child_frame_border_width);
+}
+
+/* Pixel-width of internal border.  Uses child_frame_border_width for
+   child frames if possible and falls back on internal_border_width
+   otherwise.  */
 INLINE int
 FRAME_INTERNAL_BORDER_WIDTH (struct frame *f)
 {
-  return frame_dimension (f->internal_border_width);
+#ifdef HAVE_WINDOW_SYSTEM
+  return FRAME_PARENT_FRAME(f)
+    ? (f->child_frame_border_width
+       ? FRAME_CHILD_FRAME_BORDER_WIDTH(f)
+       : frame_dimension (f->internal_border_width))
+    : frame_dimension (f->internal_border_width);
+#else
+  return frame_dimension (f->internal_border_width)
+#endif
 }
 
 /* Pixel-size of window divider lines.  */