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.

1 files changed, 12 insertions, 0 deletions

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)
 	{