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

[Manuel Giraud]

Hi,

Regarding this feature, I came up with the following patch:

diff --git a/src/xdisp.c b/src/xdisp.c
index 75d769600c4..735200fdf65 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -30985,6 +30985,24 @@ draw_glyphs (struct window *w, int x, struct glyph_row 
*row,
          }
     }
 
+  /* Update image glyphs with mouse face features.  */
+  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)
+           {
+             /* Alter the spec a bit to have a different hash for the
+                image cache.  */
+             ptrdiff_t id;
+             Lisp_Object spec = Fcopy_sequence (s->img->spec);
+             spec = nconc2 (spec, list2 (intern (":highlight"), Qt));
+             id = lookup_image (f, spec, hlinfo->mouse_face_face_id);
+             s->img = IMAGE_FROM_ID (f, id);
+           }
+    }
+
   /* Draw all strings.  */
   for (s = head; s; s = s->next)
     FRAME_RIF (f)->draw_glyph_string (s);

It does something on the an image glyph when it is hover but the image
is completely messed up.  I have stepped this code down to
svg_load_image but I do not understand what went wrong.  Any ideas?
-- 
Manuel Giraud