master 66189689ca: Fix 'window-text-pixel-size' when starting from a display property

[Eli Zaretskii]

branch: master
commit 66189689ca2f22de47e1a83af1deb9b0bff29ab7
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Fix 'window-text-pixel-size' when starting from a display property
    
    * src/xdisp.c (Fwindow_text_pixel_size): Handle the case where
    there's a display property at START and 'move_it_to' overshoots.
    (Bug#54862)
---
 src/xdisp.c | 47 +++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index bdefd2b042..6a0d0ea879 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -10957,6 +10957,7 @@ window_text_pixel_size (Lisp_Object window, Lisp_Object 
from, Lisp_Object to,
      same directionality.  */
   it.bidi_p = false;
 
+  int start_x;
   if (vertical_offset != 0)
     {
       int last_y;
@@ -10990,6 +10991,7 @@ window_text_pixel_size (Lisp_Object window, Lisp_Object 
from, Lisp_Object to,
                      + WINDOW_HEADER_LINE_HEIGHT (w));
       start = clip_to_bounds (BEGV, IT_CHARPOS (it), ZV);
       start_y = it.current_y;
+      start_x = it.current_x;
     }
   else
     {
@@ -10999,11 +11001,52 @@ window_text_pixel_size (Lisp_Object window, 
Lisp_Object from, Lisp_Object to,
       reseat_at_previous_visible_line_start (&it);
       it.current_x = it.hpos = 0;
       if (IT_CHARPOS (it) != start)
-       move_it_to (&it, start, -1, -1, -1, MOVE_TO_POS);
+       {
+         void *it1data = NULL;
+         struct it it1;
+
+         SAVE_IT (it1, it, it1data);
+         move_it_to (&it, start, -1, -1, -1, MOVE_TO_POS);
+         /* We could have a display property at START, in which case
+            asking move_it_to to stop at START will overshoot and
+            stop at position after START.  So we try again, stopping
+            before START, and account for the width of the last
+            buffer position manually.  */
+         if (IT_CHARPOS (it) > start && start > BEGV)
+           {
+             ptrdiff_t it1pos = IT_CHARPOS (it1);
+             int it1_x = it1.current_x;
+
+             RESTORE_IT (&it, &it1, it1data);
+             /* If START - 1 is the beginning of screen line,
+                move_it_to will not move, so we need to use a
+                lower-level move_it_in_display_line subroutine, and
+                tell it to move just 1 pixel, so it stops at the next
+                display element.  */
+             if (start - 1 > it1pos)
+               move_it_to (&it, start - 1, -1, -1, -1, MOVE_TO_POS);
+             else
+               move_it_in_display_line (&it, start, it1_x + 1,
+                                        MOVE_TO_POS | MOVE_TO_X);
+             move_it_to (&it, start - 1, -1, -1, -1, MOVE_TO_POS);
+             start_x = it.current_x;
+             /* If we didn't change our buffer position, the pixel
+                width of what's here was not yet accounted for; do it
+                manually.  */
+             if (IT_CHARPOS (it) == start - 1)
+               start_x += it.pixel_width;
+           }
+         else
+           {
+             start_x = it.current_x;
+             bidi_unshelve_cache (it1data, true);
+           }
+       }
+      else
+       start_x = it.current_x;
     }
 
   /* Now move to TO.  */
-  int start_x = it.current_x;
   int move_op = MOVE_TO_POS | MOVE_TO_Y;
   int to_x = -1;
   it.current_y = start_y;