bug#67794: 30.0.50; mouse-face is not respected on SVG images

[Manuel Giraud via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

[...]

> It would be a shame to waste cycles on PNG images as long as we don't
> solve this problem, so I'd prefer to enable this only for SVG and
> leave a FIXME comment about PNG.

Here is an updated version of this patch:

     - I had to export 'image_spec_value' from image.c to use it in
       xdisp.c
     - I also guard this feature behind a #ifdef HAVE_RSVG


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From afc1097a0fe0ee483bcdb2cac2045201a3f00a72 Mon Sep 17 00:00:00 2001
From: Manuel Giraud <manuel@ledu-giraud.fr>
Date: Tue, 19 Dec 2023 12:25:24 +0100
Subject: [PATCH] Respect mouse-face on SVG image glyphs (bug#67794)

* src/dispextern.h:
* src/image.c (image_spec_value): Export 'image_spec_value'.
* src/xdisp.c (draw_glyphs): Maybe update SVG image glyphs with mouse
face features before drawing.
---
 src/dispextern.h |  1 +
 src/image.c      |  2 +-
 src/xdisp.c      | 20 ++++++++++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/dispextern.h b/src/dispextern.h
index 3a4d6095f73..020c33a2628 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -3618,6 +3618,7 @@ #define TRY_WINDOW_IGNORE_FONTS_CHANGE	(1 << 1)
 bool valid_image_p (Lisp_Object);
 void prepare_image_for_display (struct frame *, struct image *);
 ptrdiff_t lookup_image (struct frame *, Lisp_Object, int);
+Lisp_Object image_spec_value (Lisp_Object, Lisp_Object, bool *);
 
 #if defined HAVE_X_WINDOWS || defined USE_CAIRO || defined HAVE_NS \
   || defined HAVE_HAIKU || defined HAVE_ANDROID
diff --git a/src/image.c b/src/image.c
index 38744fc1cce..651ec0b34e5 100644
--- a/src/image.c
+++ b/src/image.c
@@ -1543,7 +1543,7 @@ parse_image_spec (Lisp_Object spec, struct image_keyword *keywords,
    if KEY is not present in SPEC.  Set *FOUND depending on whether KEY
    was found in SPEC.  */
 
-static Lisp_Object
+Lisp_Object
 image_spec_value (Lisp_Object spec, Lisp_Object key, bool *found)
 {
   Lisp_Object tail;
diff --git a/src/xdisp.c b/src/xdisp.c
index 75d769600c4..731ad231058 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -30985,6 +30985,26 @@ draw_glyphs (struct window *w, int x, struct glyph_row *row,
 	  }
     }
 
+#ifdef HAVE_RSVG
+  /* Update SVG image glyphs with mouse face features.  FIXME: it
+     should be possible to have this behaviour with transparent
+     background PNG.  */
+  if (hl == DRAW_MOUSE_FACE)
+    {
+      Mouse_HLInfo *hlinfo = MOUSE_HL_INFO (f);
+      for (s = head; s; s = s->next)
+	if (s->first_glyph->type == IMAGE_GLYPH)
+	  if (s->img
+	      && (EQ (image_spec_value (s->img->spec, QCtype, NULL), Qsvg)))
+	    {
+	      ptrdiff_t id;
+	      id = lookup_image (f, s->img->spec, hlinfo->mouse_face_face_id);
+	      s->img = IMAGE_FROM_ID (f, id);
+	      prepare_image_for_display(f, s->img);
+	    }
+    }
+#endif
+
   /* Draw all strings.  */
   for (s = head; s; s = s->next)
     FRAME_RIF (f)->draw_glyph_string (s);
-- 
2.43.0


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-- 
Manuel Giraud