(window_scroll_pixel_based): Fix scrolling in the wrong

direction if window height was smaller than next-screen-context-lines.
Now always scroll at least one line in the requested direction.
Ensure that we actually do scroll backwards when requested to do so.

1 files changed, 16 insertions, 6 deletions

diff --git a/src/window.c b/src/window.c
index bdc105da3ed..07b197cef75 100644
--- a/src/window.c
+++ b/src/window.c
@@ -4580,7 +4580,9 @@ window_scroll_pixel_based (window, n, whole, noerror)
           int px;
           int dy = WINDOW_FRAME_LINE_HEIGHT (w);
           if (whole)
-            dy = window_box_height (w) - next_screen_context_lines * dy;
+            dy = max ((window_box_height (w)
+                       - next_screen_context_lines * dy),
+                      dy);
           dy *= n;
 
           if (n < 0 && (px = XINT (XCAR (tem))) > 0)
@@ -4615,18 +4617,26 @@ window_scroll_pixel_based (window, n, whole, noerror)
   start_display (&it, w, start);
   if (whole)
     {
-      int screen_full = (window_box_height (w)
-                         - next_screen_context_lines * FRAME_LINE_HEIGHT (it.f));
-      int dy = n * screen_full;
+      int start_pos = IT_CHARPOS (it);
+      int dy = WINDOW_FRAME_LINE_HEIGHT (w);
+      dy = max ((window_box_height (w)
+                 - next_screen_context_lines * dy),
+                dy) * n;
 
       /* Note that move_it_vertically always moves the iterator to the
          start of a line.  So, if the last line doesn't have a newline,
          we would end up at the start of the line ending at ZV.  */
       if (dy <= 0)
-        move_it_vertically_backward (&it, -dy);
+        {
+          move_it_vertically_backward (&it, -dy);
+          /* Ensure we actually does move, e.g. in case we are currently
+             looking at an image that is taller that the window height.  */
+          while (start_pos == IT_CHARPOS (it)
+                 && start_pos > BEGV)
+            move_it_by_lines (&it, -1, 1);
+        }
       else if (dy > 0)
         {
-          int start_pos = IT_CHARPOS (it);
           move_it_to (&it, ZV, -1, it.current_y + dy, -1,
                       MOVE_TO_POS | MOVE_TO_Y);
           /* Ensure we actually does move, e.g. in case we are currently