2 files changed, 28 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 5131f666c6e..1a83531ad10 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,12 @@
+2013-08-15  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (compute_window_start_on_continuation_line): When
+        WORD_WRAP is in effect, use move_it_to instead of move_it_by_lines
+        to make sure we end up setting the window start at the leftmost
+        visible character of the display line.  This avoids funky
+        horizontal shifting because the window start is not kept on the
+        same position.  (Bug#15090)
+
 2013-08-15  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
         * image.c (imagemagick_compute_animated_image): Implement animated
diff --git a/src/xdisp.c b/src/xdisp.c
index 4d0b0ab9974..8b72c58cd07 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -14912,7 +14912,25 @@ compute_window_start_on_continuation_line (struct window *w)
             {
               min_distance = distance;
               pos = it.current.pos;
-              move_it_by_lines (&it, 1);
+              if (it.line_wrap == WORD_WRAP)
+                {
+                  /* Under WORD_WRAP, move_it_by_lines is likely to
+                     overshoot and stop not at the first, but the
+                     second character from the left margin.  So in
+                     that case, we need a more tight control on the X
+                     coordinate of the iterator than move_it_by_lines
+                     promises in its contract.  The method is to first
+                     go to the last (rightmost) visible character of a
+                     line, then move to the leftmost character on the
+                     next line in a separate call.  */
+                  move_it_to (&it, ZV, it.last_visible_x, it.current_y, -1,
+                              MOVE_TO_POS | MOVE_TO_X | MOVE_TO_Y);
+                  move_it_to (&it, ZV, 0,
+                              it.current_y + it.max_ascent + it.max_descent, -1,
+                              MOVE_TO_POS | MOVE_TO_X | MOVE_TO_Y);
+                }
+              else
+                move_it_by_lines (&it, 1);
             }
 
           /* Set the window start there.  */