Fix 'recenter' when visual-line-mode is turned on

* src/window.c (Frecenter): Use the same code for GUI and TTY
frames alike; use vmotion only for "initial" frames.  This is
because vmotion doesn't support visual-line-mode.  Rewrite the
'iarg >= 0' case to use move_it_* functions instead of using
vmotion, for the same reason.  Fix the clipping of the argument
value to support scroll-margin in all cases and avoid unwarranted
recentering.  Reported by Milan Stanojević <milanst@gmail.com> in
http://lists.gnu.org/archive/html/help-gnu-emacs/2015-04/msg00092.html,
which see.

1 files changed, 31 insertions, 10 deletions

diff --git a/src/window.c b/src/window.c
index d59616d0545..55fcb8cf02f 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5799,10 +5799,9 @@ and redisplay normally--don't erase and redraw the frame.  */)
   this_scroll_margin
     = max (0, min (scroll_margin, w->total_lines / 4));
 
-  /* Handle centering on a graphical frame specially.  Such frames can
-     have variable-height lines and centering point on the basis of
-     line counts would lead to strange effects.  */
-  if (FRAME_WINDOW_P (XFRAME (w->frame)))
+  /* Don't use redisplay code for initial frames, as the necessary
+     data structures might not be set up yet then.  */
+  if (!FRAME_INITIAL_P (XFRAME (w->frame)))
     {
       if (center_p)
         {
@@ -5824,9 +5823,11 @@ and redisplay normally--don't erase and redraw the frame.  */)
           ptrdiff_t nlines = min (PTRDIFF_MAX, -iarg);
           int extra_line_spacing;
           int h = window_box_height (w);
+          int ht = window_internal_height (w);
           void *itdata = bidi_shelve_cache ();
 
-          iarg = - max (-iarg, this_scroll_margin);
+          nlines = clip_to_bounds (this_scroll_margin + 1, nlines,
+                                   ht - this_scroll_margin);
 
           SET_TEXT_POS (pt, PT, PT_BYTE);
           start_display (&it, w, pt);
@@ -5890,13 +5891,33 @@ and redisplay normally--don't erase and redraw the frame.  */)
         }
       else
         {
-          struct position pos;
+          struct it it;
+          struct text_pos pt;
+          ptrdiff_t nlines = min (PTRDIFF_MAX, iarg);
+          int ht = window_internal_height (w);
+          void *itdata = bidi_shelve_cache ();
+
+          nlines = clip_to_bounds (this_scroll_margin, nlines,
+                                   ht - this_scroll_margin - 1);
+
+          SET_TEXT_POS (pt, PT, PT_BYTE);
+          start_display (&it, w, pt);
 
-          iarg = max (iarg, this_scroll_margin);
+          /* Move to the beginning of screen line containing PT.  */
+          move_it_by_lines (&it, 0);
+
+          /* Move back to find the point which is ARG screen lines above PT.  */
+          if (nlines > 0)
+            {
+              it.current_y = 0;
+              it.vpos = 0;
+              move_it_by_lines (&it, -nlines);
+            }
 
-          pos = *vmotion (PT, PT_BYTE, -iarg, w);
-          charpos = pos.bufpos;
-          bytepos = pos.bytepos;
+          charpos = IT_CHARPOS (it);
+          bytepos = IT_BYTEPOS (it);
+
+          bidi_unshelve_cache (itdata, 0);
         }
     }
   else