Recompute :map when image :scale, :rotation, or :flip changes

Now, when transforming an image, its :map is recomputed to fit.
Image map coordinates are integers, so when computing :map,
coordinates are rounded.  To prevent an image from drifting from
its map after repeated transformations, 'create-image' now adds
a new image property :original-map, which is combined with the
image's transformation parameters to recompute :map.

* lisp/image.el (image-recompute-map-p): Add user option to
control whether :map is recomputed when an image is transformed.
(create-image): Create :map from :original-map and vice versa.
(image--delayed-change-size): Fix comment.
(image--change-size, image-rotate, image-flip-horizontally,
image-flip-vertically): Recompute image map after transformation
and mention 'image-recompute-map-p' in docstring.
(image--compute-map): Add function to compute a map from original
map.
(image--compute-original-map): Add function to compute an
original map from map.
(image--scale-map): Add function to scale a map based on :scale.
(image--rotate-map): Add function to rotate a map based on
:rotation.
(image--rotate-coord): Add function to rotate a map coordinate
pair.
(image--flip-map): Add function to flip a map based on :flip.
(image-increase-size, image-decrease-size, image-mouse-increase-size)
(image-mouse-decrease-size): Mention 'image-recompute-map-p' in
docstrings.
* etc/NEWS: Add NEWS entry.
* doc/lispref/display.texi (Image Descriptors): Document :original-map
and new user option 'image-recompute-map-p'.
* test/lisp/image-tests.el (image--compute-map-and-original-map):
Test 'image--compute-map' and 'image--compute-original-map'.
(image-tests--map-equal): Add equality predicate to compare image maps.
(image-create-image-with-map): Test that 'create-image' adds :map
and/or :original-map as appropriate.
(image-transform-map): Test functions related to transforming maps.
(Bug#69602)

1 files changed, 12 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index c6b654a9d3b..19588fe8eeb 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1368,6 +1368,18 @@ without specifying a file, like this:
     (notifications-notify
       :title "I am playing music" :app-icon 'multimedia-player)
 
+** Image
+
++++
+*** Image :map property is now recomputed when image is transformed.
+Now images with clickable maps work as expected after you run commands
+such as `image-increase-size', `image-decrease-size', `image-rotate',
+`image-flip-horizontally', and `image-flip-vertically'.
+
++++
+*** New user option 'image-recompute-map-p'
+Set this option to nil to prevent Emacs from recomputing image maps.
+
 ** Image Dired
 
 *** New user option 'image-dired-thumb-naming'.