Fix bug #17905 with display of point in partially visible line at end of window.

 src/xdisp.c (redisplay_window): If redisplay of a window ends up
 with point in a partially visible line at end of the window, make
 sure the amended position of point actually has smaller Y
 coordinate; if not, give up and scroll the display.
 src/window.c (window_scroll_pixel_based): When point ends up at the
 last fully visible line, don't let move_it_to stop at the left
 edge of the line and dupe us into thinking point is inside the
 scroll margin.

3 files changed, 48 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 24343faa407..a88c6caacfd 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,15 @@
 2014-07-04  Eli Zaretskii  <eliz@gnu.org>
 
+        * xdisp.c (redisplay_window): If redisplay of a window ends up
+        with point in a partially visible line at end of the window, make
+        sure the amended position of point actually has smaller Y
+        coordinate; if not, give up and scroll the display.  (Bug#17905)
+
+        * window.c (window_scroll_pixel_based): When point ends up at the
+        last fully visible line, don't let move_it_to stop at the left
+        edge of the line and dupe us into thinking point is inside the
+        scroll margin.
+
         * w32.c (network_interface_info): Make sure the argument is a
         Lisp string.
 
diff --git a/src/window.c b/src/window.c
index 8e8252d3b76..5e9dd0ec718 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5167,6 +5167,32 @@ window_scroll_pixel_based (Lisp_Object window, int n, bool whole, int noerror)
       charpos = IT_CHARPOS (it);
       bytepos = IT_BYTEPOS (it);
 
+      /* If PT is in the screen line at the last fully visible line,
+         move_it_to will stop at X = 0 in that line, because the
+         required Y coordinate is reached there.  See if we can get to
+         PT without descending lower in Y, and if we can, it means we
+         reached PT before the scroll margin.  */
+      if (charpos != PT)
+        {
+          struct it it2;
+          void *it_data;
+
+          it2 = it;
+          it_data = bidi_shelve_cache ();
+          move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
+          if (IT_CHARPOS (it) == PT && it.current_y == it2.current_y)
+            {
+              charpos = IT_CHARPOS (it);
+              bytepos = IT_BYTEPOS (it);
+              bidi_unshelve_cache (it_data, 1);
+            }
+          else
+            {
+              it = it2;
+              bidi_unshelve_cache (it_data, 0);
+            }
+        }
+
       /* See if point is on a partially visible line at the end.  */
       if (it.what == IT_EOB)
         partial_p = it.current_y + it.ascent + it.descent > it.last_visible_y;
diff --git a/src/xdisp.c b/src/xdisp.c
index 459edf4367f..fe5d0f579d8 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -16106,6 +16106,18 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
           /* Point does appear, but on a line partly visible at end of window.
              Move it back to a fully-visible line.  */
           new_vpos = window_box_height (w);
+          /* But if window_box_height suggests a Y coordinate that is
+             not less than we already have, that line will clearly not
+             be fully visible, so give up and scroll the display.
+             This can happen when the default face uses a font whose
+             dimensions are different from the frame's default
+             font.  */
+          if (new_vpos >= w->cursor.y)
+            {
+              w->cursor.vpos = -1;
+              clear_glyph_matrix (w->desired_matrix);
+              goto try_to_scroll;
+            }
         }
       else if (w->cursor.vpos >= 0)
         {