Fix glyph string generation for multi-font compositions (Bug#26742)

* src/xdisp.c (glyph_string_containing_background_width): New function.
(draw_glyphs): Use it to get correct background width.
(compute_overhangs_and_x): Don't change x in the middle of composite
characters.

1 files changed, 25 insertions, 3 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 41458c38176..c730cdae054 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -25421,6 +25421,20 @@ set_glyph_string_background_width (struct glyph_string *s, int start, int last_x
 }
 
 
+/* Return glyph string that shares background with glyph string S and
+   whose `background_width' member has been set.  */
+
+static struct glyph_string *
+glyph_string_containing_background_width (struct glyph_string *s)
+{
+  if (s->cmp)
+    while (s->cmp_from)
+      s = s->prev;
+
+  return s;
+}
+
+
 /* Compute overhangs and x-positions for glyph string S and its
    predecessors, or successors.  X is the starting x-position for S.
    BACKWARD_P means process predecessors.  */
@@ -25434,7 +25448,8 @@ compute_overhangs_and_x (struct glyph_string *s, int x, bool backward_p)
         {
           if (FRAME_RIF (s->f)->compute_glyph_string_overhangs)
             FRAME_RIF (s->f)->compute_glyph_string_overhangs (s);
-          x -= s->width;
+          if (!s->cmp || s->cmp_to == s->cmp->glyph_len)
+            x -= s->width;
           s->x = x;
           s = s->prev;
         }
@@ -25446,7 +25461,8 @@ compute_overhangs_and_x (struct glyph_string *s, int x, bool backward_p)
           if (FRAME_RIF (s->f)->compute_glyph_string_overhangs)
             FRAME_RIF (s->f)->compute_glyph_string_overhangs (s);
           s->x = x;
-          x += s->width;
+          if (!s->cmp || s->cmp_to == s->cmp->glyph_len)
+            x += s->width;
           s = s->next;
         }
     }
@@ -25778,7 +25794,10 @@ draw_glyphs (struct window *w, int x, struct glyph_row *row,
   USE_SAFE_ALLOCA;
   BUILD_GLYPH_STRINGS (i, end, head, tail, hl, x, last_x);
   if (tail)
-    x_reached = tail->x + tail->background_width;
+    {
+      s = glyph_string_containing_background_width (tail);
+      x_reached = s->x + s->background_width;
+    }
   else
     x_reached = x;
 
@@ -25933,6 +25952,9 @@ draw_glyphs (struct window *w, int x, struct glyph_row *row,
           compute_overhangs_and_x (h, tail->x + tail->width, false);
           append_glyph_string_lists (&head, &tail, h, t);
         }
+      tail = glyph_string_containing_background_width (tail);
+      if (clip_tail)
+        clip_tail = glyph_string_containing_background_width (clip_tail);
       if (clip_head || clip_tail)
         for (s = head; s; s = s->next)
           {