[Emacs-diffs] Changes to emacs/src/window.c

[Chong Yidong]

Index: emacs/src/window.c
diff -u emacs/src/window.c:1.536 emacs/src/window.c:1.537
--- emacs/src/window.c:1.536    Wed Feb 22 21:01:34 2006
+++ emacs/src/window.c  Tue Feb 28 14:52:46 2006
@@ -50,6 +50,7 @@
 
 
 Lisp_Object Qwindowp, Qwindow_live_p, Qwindow_configuration_p;
+Lisp_Object Qscroll_up, Qscroll_down;
 Lisp_Object Qwindow_size_fixed;
 extern Lisp_Object Qleft_margin, Qright_margin;
 
@@ -4721,9 +4722,9 @@
   struct text_pos start;
   Lisp_Object tem;
   int this_scroll_margin;
-  int preserve_y;
   /* True if we fiddled the window vscroll field without really scrolling.   */
   int vscrolled = 0;
+  static int preserve_y = -1;
 
   SET_TEXT_POS_FROM_MARKER (start, w->start);
 
@@ -4787,9 +4788,18 @@
      point in the same window line as it is now, so get that line.  */
   if (!NILP (Vscroll_preserve_screen_position))
     {
-      start_display (&it, w, start);
-      move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
-      preserve_y = it.current_y;
+      /* We preserve the goal pixel coordinate across consecutive
+        calls to scroll-up or scroll-down.  This avoids the
+        possibility of point becoming "stuck" on a tall line when
+        scrolling by one line.  */
+      if (preserve_y < 0
+         || (current_kboard->Vlast_command != Qscroll_up
+             && current_kboard->Vlast_command != Qscroll_down))
+       {
+         start_display (&it, w, start);
+         move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
+         preserve_y = it.current_y;
+       }
     }
   else
     preserve_y = -1;
@@ -4926,10 +4936,9 @@
        {
          /* If we have a header line, take account of it.
             This is necessary because we set it.current_y to 0, above.  */
-         if (WINDOW_WANTS_HEADER_LINE_P (w))
-           preserve_y -= CURRENT_HEADER_LINE_HEIGHT (w);
-
-         move_it_to (&it, -1, -1, preserve_y, -1, MOVE_TO_Y);
+         move_it_to (&it, -1, -1,
+                     preserve_y - (WINDOW_WANTS_HEADER_LINE_P (w) ? 1 : 0 ),
+                     -1, MOVE_TO_Y);
          SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
        }
       else
@@ -4983,15 +4992,9 @@
        {
          SET_TEXT_POS_FROM_MARKER (start, w->start);
          start_display (&it, w, start);
-#if 0  /* It's wrong to subtract this here
-         because we called start_display again
-         and did not alter it.current_y this time.  */
-
-         /* If we have a header line, take account of it.  */
-         if (WINDOW_WANTS_HEADER_LINE_P (w))
-           preserve_y -= CURRENT_HEADER_LINE_HEIGHT (w);
-#endif
-
+         /* It would be wrong to subtract CURRENT_HEADER_LINE_HEIGHT
+            here because we called start_display again and did not
+            alter it.current_y this time.  */
          move_it_to (&it, -1, -1, preserve_y, -1, MOVE_TO_Y);
          SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
        }
@@ -6988,6 +6991,12 @@
 void
 syms_of_window ()
 {
+  Qscroll_up = intern ("scroll-up");
+  staticpro (&Qscroll_up);
+
+  Qscroll_down = intern ("scroll-down");
+  staticpro (&Qscroll_down);
+
   Qwindow_size_fixed = intern ("window-size-fixed");
   staticpro (&Qwindow_size_fixed);
   Fset (Qwindow_size_fixed, Qnil);