Add variable `scroll-preserve-screen-position-commands'.

http://lists.gnu.org/archive/html/emacs-devel/2010-04/msg00403.html

* window.c (Vscroll_preserve_screen_position_commands): New variable
with the default value as the list of Qscroll_down and Qscroll_up.
(window_scroll_pixel_based, window_scroll_line_based): Search the
last command in the list Vscroll_preserve_screen_position_commands
instead of comparing with Qscroll_up and Qscroll_down.

* mwheel.el (scroll-preserve-screen-position-commands):
Add mwheel-scroll to this list of commands.

* simple.el (scroll-preserve-screen-position-commands):
Add scroll-up-command, scroll-down-command, scroll-up-line,
scroll-down-line to this list of commands.

1 files changed, 19 insertions, 5 deletions

diff --git a/src/window.c b/src/window.c
index f17a645f82c..2757b98ddd9 100644
--- a/src/window.c
+++ b/src/window.c
@@ -168,6 +168,10 @@ static Lisp_Object Vwindow_configuration_change_hook;
 
 Lisp_Object Vscroll_preserve_screen_position;
 
+/* List of commands affected by `Vscroll_preserve_screen_position'.  */
+
+Lisp_Object Vscroll_preserve_screen_position_commands;
+
 /* Non-nil means that text is inserted before window's markers.  */
 
 Lisp_Object Vwindow_point_insertion_type;
@@ -4946,8 +4950,8 @@ window_scroll_pixel_based (window, n, whole, noerror)
          possibility of point becoming "stuck" on a tall line when
          scrolling by one line.  */
       if (window_scroll_pixel_based_preserve_y < 0
-          || (!EQ (current_kboard->Vlast_command, Qscroll_up)
-              && !EQ (current_kboard->Vlast_command, Qscroll_down)))
+          || NILP (Fmemq (current_kboard->Vlast_command,
+                          Vscroll_preserve_screen_position_commands)))
         {
           start_display (&it, w, start);
           move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
@@ -5207,8 +5211,8 @@ window_scroll_line_based (window, n, whole, noerror)
   if (!NILP (Vscroll_preserve_screen_position))
     {
       if (window_scroll_preserve_vpos <= 0
-          || (!EQ (current_kboard->Vlast_command, Qscroll_up)
-              && !EQ (current_kboard->Vlast_command, Qscroll_down)))
+          || NILP (Fmemq (current_kboard->Vlast_command,
+                          Vscroll_preserve_screen_position_commands)))
         {
           struct position posit
             = *compute_motion (startpos, 0, 0, 0,
@@ -7265,9 +7269,19 @@ at the scroll margin or window boundary respectively.
 A value of t means point keeps its screen position if the scroll
 command moved it vertically out of the window, e.g. when scrolling
 by full screens.
-Any other value means point always keeps its screen position.  */);
+Any other value means point always keeps its screen position.
+Scroll commands are defined by the variable
+`scroll-preserve-screen-position-commands'.  */);
   Vscroll_preserve_screen_position = Qnil;
 
+  DEFVAR_LISP ("scroll-preserve-screen-position-commands",
+               &Vscroll_preserve_screen_position_commands,
+               doc: /* A list of commands whose scrolling should keep screen position unchanged.
+This list defines the names of scroll commands affected by the variable
+`scroll-preserve-screen-position'.  */);
+  Vscroll_preserve_screen_position_commands =
+    Fcons (Qscroll_down, Fcons (Qscroll_up, Qnil));
+
   DEFVAR_LISP ("window-point-insertion-type", &Vwindow_point_insertion_type,
                doc: /* Type of marker to use for `window-point'.  */);
   Vwindow_point_insertion_type = Qnil;