(redisplay_window): If current window start is not at the

beginning of a line, select a new window start if buffer is modified
and window start is in the modified region, but the first change is
before window start.

1 files changed, 27 insertions, 0 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 075e05b0e13..db987ad5a90 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -12860,6 +12860,33 @@ redisplay_window (window, just_this_one_p)
                || (XFASTINT (w->last_modified) >= MODIFF
                    && XFASTINT (w->last_overlay_modified) >= OVERLAY_MODIFF)))
     {
+
+      /* If first window line is a continuation line, and window start
+         is inside the modified region, but the first change is before
+         current window start, we must select a new window start.*/
+      if (NILP (w->start_at_line_beg))
+        {
+          /* Make sure beg_unchanged and end_unchanged are up to date.
+             Do it only if buffer has really changed.  This may or may
+             not have been done by try_window_id (see which) already. */
+          if (MODIFF > SAVE_MODIFF
+              /* This seems to happen sometimes after saving a buffer.  */
+              || BEG_UNCHANGED + END_UNCHANGED > Z_BYTE)
+            {
+              if (GPT - BEG < BEG_UNCHANGED)
+                BEG_UNCHANGED = GPT - BEG;
+              if (Z - GPT < END_UNCHANGED)
+                END_UNCHANGED = Z - GPT;
+            }
+
+          if (CHARPOS (startp) > BEG + BEG_UNCHANGED
+              && CHARPOS (startp) <= Z - END_UNCHANGED)
+            {
+              centering_position = 0;
+              goto recenter;
+            }
+        }
+
 #if GLYPH_DEBUG
       debug_method_add (w, "same window start");
 #endif