Fix bug #12403 with garbled display under non-zero scroll-margin.

 src/xdisp.c (try_window_reusing_current_matrix): Under bidi
 reordering, locate the cursor by calling set_cursor_from_row; if
 that fails, clear the desired glyph matrix before returning a
 failure indication to the caller.  Fixes leaving garbled display
 when fast scrolling with a down-key when scroll-margin is non-zero.

2 files changed, 31 insertions, 18 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 49c1fa345bb..39bdd191188 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2012-09-12  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (try_window_reusing_current_matrix): Under bidi
+        reordering, locate the cursor by calling set_cursor_from_row; if
+        that fails, clear the desired glyph matrix before returning a
+        failure indication to the caller.  Fixes leaving garbled display
+        when fast scrolling with a down-key.  (Bug#12403)
+
 2012-09-12  Jan Djärv  <jan.h.d@swipnet.se>
 
         * gtkutil.c (x_wm_set_size_hint): Use 1 col for base_width so it
diff --git a/src/xdisp.c b/src/xdisp.c
index 6762bf85eb4..3fab4b54cf0 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -16593,28 +16593,33 @@ try_window_reusing_current_matrix (struct window *w)
             }
           if (row < bottom_row)
             {
-              struct glyph *glyph = row->glyphs[TEXT_AREA] + w->cursor.hpos;
-              struct glyph *end = row->glyphs[TEXT_AREA] + row->used[TEXT_AREA];
-
-              /* Can't use this optimization with bidi-reordered glyph
-                 rows, unless cursor is already at point. */
+              /* Can't simply scan the row for point with
+                 bidi-reordered glyph rows.  Let set_cursor_from_row
+                 figure out where to put the cursor, and if it fails,
+                 give up.  */
               if (!NILP (BVAR (XBUFFER (w->buffer), bidi_display_reordering)))
                 {
-                  if (!(w->cursor.hpos >= 0
-                        && w->cursor.hpos < row->used[TEXT_AREA]
-                        && BUFFERP (glyph->object)
-                        && glyph->charpos == PT))
-                    return 0;
+                  if (!set_cursor_from_row (w, row, w->current_matrix,
+                                            0, 0, 0, 0))
+                    {
+                      clear_glyph_matrix (w->desired_matrix);
+                      return 0;
+                    }
                 }
               else
-                for (; glyph < end
-                       && (!BUFFERP (glyph->object)
-                           || glyph->charpos < PT);
-                     glyph++)
-                  {
-                    w->cursor.hpos++;
-                    w->cursor.x += glyph->pixel_width;
-                  }
+                {
+                  struct glyph *glyph = row->glyphs[TEXT_AREA] + w->cursor.hpos;
+                  struct glyph *end = row->glyphs[TEXT_AREA] + row->used[TEXT_AREA];
+
+                  for (; glyph < end
+                         && (!BUFFERP (glyph->object)
+                             || glyph->charpos < PT);
+                       glyph++)
+                    {
+                      w->cursor.hpos++;
+                      w->cursor.x += glyph->pixel_width;
+                    }
+                }
             }
         }