Merge from emacs-24

[gnu-emacs] / src / window.c

diff --git a/src/window.c b/src/window.c
index e4ff2b418060d048b888de59391a2edfe4fe8512..7c2b3ca29d20c5a4fea21a286b11d9eb3b4b50c0 100644 (file)
--- a/src/window.c
+++ b/src/window.c
@@ -4950,9 +4950,14 @@ window_scroll_pixel_based (Lisp_Object window, int n, bool whole, int noerror)
        {
          int px;
          int dy = frame_line_height;
+         /* In the below we divide the window box height by the
+            frame's line height to make the result predictable when
+            the window box is not an integral multiple of the line
+            height.  This is important to ensure we get back to the
+            same position when scrolling up, then down.  */
          if (whole)
-           dy = max ((window_box_height (w)
-                      - next_screen_context_lines * dy),
+           dy = max ((window_box_height (w) / dy
+                      - next_screen_context_lines) * dy,
                      dy);
          dy *= n;
 
@@ -5034,9 +5039,12 @@ window_scroll_pixel_based (Lisp_Object window, int n, bool whole, int noerror)
     {
       ptrdiff_t start_pos = IT_CHARPOS (it);
       int dy = frame_line_height;
-
-      dy = max ((window_box_height (w)
-                - next_screen_context_lines * dy),
+      /* In the below we divide the window box height by the frame's
+        line height to make the result predictable when the window
+        box is not an integral multiple of the line height.  This is
+        important to ensure we get back to the same position when
+        scrolling up, then down.  */
+      dy = max ((window_box_height (w) / dy - next_screen_context_lines) * dy,
                dy) * n;
 
       /* Note that move_it_vertically always moves the iterator to the