Fix bug #12811 with scrolling under scroll-up/down-aggressively.

 src/xdisp.c (try_scrolling): Fix correction of aggressive-scroll
 amount when the scroll margins are too large.  When scrolling
 backwards in the buffer, give up if cannot reach point or the
 scroll margin within a reasonable number of screen lines.  Fixes
 point position in window under scroll-up/down-aggressively when
 point is positioned many lines beyond the window top/bottom.

2 files changed, 34 insertions, 16 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index c49039a3cf9..11e657cffa9 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,13 @@
+2012-11-06  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (try_scrolling): Fix correction of aggressive-scroll
+        amount when the scroll margins are too large.  When scrolling
+        backwards in the buffer, give up if cannot reach point or the
+        scroll margin within a reasonable number of screen lines.  Fixes
+        point position in window under scroll-up/down-aggressively when
+        point is positioned many lines beyond the window top/bottom.
+        (Bug#12811)
+
 2012-11-05  Eli Zaretskii  <eliz@gnu.org>
 
         * ralloc.c (relinquish): If real_morecore fails to return memory
diff --git a/src/xdisp.c b/src/xdisp.c
index bc1cbd94bd5..c7195504c4c 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -14791,13 +14791,18 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
           if (NUMBERP (aggressive))
             {
               double float_amount = XFLOATINT (aggressive) * height;
-              amount_to_scroll = float_amount;
-              if (amount_to_scroll == 0 && float_amount > 0)
-                amount_to_scroll = 1;
+              int aggressive_scroll = float_amount;
+              if (aggressive_scroll == 0 && float_amount > 0)
+                aggressive_scroll = 1;
               /* Don't let point enter the scroll margin near top of
-                 the window.  */
-              if (amount_to_scroll > height - 2*this_scroll_margin + dy)
-                amount_to_scroll = height - 2*this_scroll_margin + dy;
+                 the window.  This could happen if the value of
+                 scroll_up_aggressively is too large and there are
+                 non-zero margins, because scroll_up_aggressively
+                 means put point that fraction of window height
+                 _from_the_bottom_margin_.  */
+              if (aggressive_scroll + 2*this_scroll_margin > height)
+                aggressive_scroll = height - 2*this_scroll_margin;
+              amount_to_scroll = dy + aggressive_scroll;
             }
         }
 
@@ -14857,7 +14862,8 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
           /* Compute the vertical distance from PT to the scroll
              margin position.  Move as far as scroll_max allows, or
              one screenful, or 10 screen lines, whichever is largest.
-             Give up if distance is greater than scroll_max.  */
+             Give up if distance is greater than scroll_max or if we
+             didn't reach the scroll margin position.  */
           SET_TEXT_POS (pos, PT, PT_BYTE);
           start_display (&it, w, pos);
           y0 = it.current_y;
@@ -14867,7 +14873,8 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
                       y_to_move, -1,
                       MOVE_TO_POS | MOVE_TO_X | MOVE_TO_Y);
           dy = it.current_y - y0;
-          if (dy > scroll_max)
+          if (dy > scroll_max
+              || IT_CHARPOS (it) < CHARPOS (scroll_margin_pos))
             return SCROLLING_FAILED;
 
           /* Compute new window start.  */
@@ -14885,15 +14892,16 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
               if (NUMBERP (aggressive))
                 {
                   double float_amount = XFLOATINT (aggressive) * height;
-                  amount_to_scroll = float_amount;
-                  if (amount_to_scroll == 0 && float_amount > 0)
-                    amount_to_scroll = 1;
-                  amount_to_scroll -=
-                    this_scroll_margin - dy - FRAME_LINE_HEIGHT (f);
+                  int aggressive_scroll = float_amount;
+                  if (aggressive_scroll == 0 && float_amount > 0)
+                    aggressive_scroll = 1;
                   /* Don't let point enter the scroll margin near
-                     bottom of the window.  */
-                  if (amount_to_scroll > height - 2*this_scroll_margin + dy)
-                    amount_to_scroll = height - 2*this_scroll_margin + dy;
+                     bottom of the window, if the value of
+                     scroll_down_aggressively happens to be too
+                     large.  */
+                  if (aggressive_scroll + 2*this_scroll_margin > height)
+                    aggressive_scroll = height - 2*this_scroll_margin;
+                  amount_to_scroll = dy + aggressive_scroll;
                 }
             }