Fix failures in try_scrolling when scrolling back.

 src/xdisp.c (try_scrolling): When point is above the window, allow
 searching as far as scroll_max, or one screenful, to compute
 vertical distance from PT to the scroll margin position.  This
 prevents try_scrolling from unnecessarily failing when
 scroll-conservatively is set to a value slightly larger than the
 window height.

2 files changed, 16 insertions, 4 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index e7a93ab7819..cb9096a5a5c 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,12 @@
+2011-03-28  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (try_scrolling): When point is above the window, allow
+        searching as far as scroll_max, or one screenful, to compute
+        vertical distance from PT to the scroll margin position.  This
+        prevents try_scrolling from unnecessarily failing when
+        scroll-conservatively is set to a value slightly larger than the
+        window height.
+
 2011-03-27  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (try_scrolling): Clean up the case of PT below the
diff --git a/src/xdisp.c b/src/xdisp.c
index 1b72f2e3081..871d070ed31 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -13176,16 +13176,19 @@ try_scrolling (Lisp_Object window, int just_this_one_p,
         {
           /* Point is in the scroll margin at the top of the window or
              above what is displayed in the window.  */
-          int y0;
+          int y0, y_to_move;
 
           /* Compute the vertical distance from PT to the scroll
-             margin position.  Give up if distance is greater than
-             scroll_max.  */
+             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.  */
           SET_TEXT_POS (pos, PT, PT_BYTE);
           start_display (&it, w, pos);
           y0 = it.current_y;
+          y_to_move = max (it.last_visible_y,
+                           max (scroll_max, 10 * FRAME_LINE_HEIGHT (f)));
           move_it_to (&it, CHARPOS (scroll_margin_pos), 0,
-                      it.last_visible_y, -1,
+                      y_to_move, -1,
                       MOVE_TO_POS | MOVE_TO_X | MOVE_TO_Y);
           dy = it.current_y - y0;
           if (dy > scroll_max)