Avoid recentering when lines differ in their height.

 xdisp.c (try_scrolling): When scroll-conservatively is set to
 most-positive-fixnum, be extra accurate when scrolling window
 start, to avoid missing the cursor line.

2 files changed, 26 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 7d875bf5bda..7405d92e0e6 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2010-06-20  Eli Zaretskii  <eliz@gnu.org>
+
+        * xdisp.c (try_scrolling): When scroll-conservatively is set to
+        most-positive-fixnum, be extra accurate when scrolling window
+        start, to avoid missing the cursor line.
+
 2010-06-19  Eli Zaretskii  <eliz@gnu.org>
 
         * xdisp.c (try_scrolling): Compute the limit for searching point
diff --git a/src/xdisp.c b/src/xdisp.c
index d533346c3b6..795e13e6f1a 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -13486,7 +13486,26 @@ try_scrolling (window, just_this_one_p, scroll_conservatively,
         return SCROLLING_FAILED;
 
       start_display (&it, w, startp);
-      move_it_vertically (&it, amount_to_scroll);
+      if (scroll_max < INT_MAX)
+        move_it_vertically (&it, amount_to_scroll);
+      else
+        {
+          /* Extra precision for users who set scroll-conservatively
+             to most-positive-fixnum: make sure the amount we scroll
+             the window start is never less than amount_to_scroll,
+             which was computed as distance from window bottom to
+             point.  This matters when lines at window top and lines
+             below window bottom have different height.  */
+          struct it it1 = it;
+          /* We use a temporary it1 because line_bottom_y can modify
+             its argument, if it moves one line down; see there.  */
+          int start_y = line_bottom_y (&it1);
+
+          do {
+            move_it_by_lines (&it, 1, 1);
+            it1 = it;
+          } while (line_bottom_y (&it1) - start_y < amount_to_scroll);
+        }
 
       /* If STARTP is unchanged, move it down another screen line.  */
       if (CHARPOS (it.current.pos) == CHARPOS (startp))