* window.c (window_scroll_pixel_based_preserve_x)

(window_scroll_preserve_hpos, window_scroll_preserve_vpos): New vars.
(window_scroll_pixel_based, window_scroll_line_based):
Use them to preserve column positions.
(syms_of_window): Initialize them.
* indent.c (Fvertical_motion): Extend first arg to allow passing an
(HPOS . VPOS) pair.
* xdisp.c (move_it_in_display_line_to): Improve the type of its args.
(move_it_in_display_line): New wrapper.
* dispextern.h (move_it_in_display_line): Declare.

1 files changed, 41 insertions, 16 deletions

diff --git a/src/window.c b/src/window.c
index 095e8412aa8..9385b307b9e 100644
--- a/src/window.c
+++ b/src/window.c
@@ -224,8 +224,14 @@ int window_deletion_count;
 
 /* Used by the function window_scroll_pixel_based */
 
+static int window_scroll_pixel_based_preserve_x;
 static int window_scroll_pixel_based_preserve_y;
 
+/* Same for window_scroll_line_based.  */
+
+static int window_scroll_preserve_hpos;
+static int window_scroll_preserve_vpos;
+
 #if 0 /* This isn't used anywhere.  */
 /* Nonzero means we can split a frame even if it is "unsplittable".  */
 static int inhibit_frame_unsplittable;
@@ -5216,10 +5222,12 @@ window_scroll_pixel_based (window, n, whole, noerror)
           start_display (&it, w, start);
           move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
           window_scroll_pixel_based_preserve_y = it.current_y;
+          window_scroll_pixel_based_preserve_x = it.current_x;
         }
     }
   else
-    window_scroll_pixel_based_preserve_y = -1;
+    window_scroll_pixel_based_preserve_y
+      = window_scroll_pixel_based_preserve_x = -1;
 
   /* Move iterator it from start the specified distance forward or
      backward.  The result is the new window start.  */
@@ -5355,10 +5363,11 @@ window_scroll_pixel_based (window, n, whole, noerror)
         {
           /* If we have a header line, take account of it.
              This is necessary because we set it.current_y to 0, above.  */
-          move_it_to (&it, -1, -1,
+          move_it_to (&it, -1,
+                      window_scroll_pixel_based_preserve_x,
                       window_scroll_pixel_based_preserve_y
                       - (WINDOW_WANTS_HEADER_LINE_P (w) ? 1 : 0 ),
-                      -1, MOVE_TO_Y);
+                      -1, MOVE_TO_Y | MOVE_TO_X);
           SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
         }
       else
@@ -5416,8 +5425,9 @@ window_scroll_pixel_based (window, n, whole, noerror)
           /* 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, window_scroll_pixel_based_preserve_y, -1,
-                      MOVE_TO_Y);
+          move_it_to (&it, -1, window_scroll_pixel_based_preserve_x,
+                      window_scroll_pixel_based_preserve_y, -1,
+                      MOVE_TO_Y | MOVE_TO_X);
           SET_PT_BOTH (IT_CHARPOS (it), IT_BYTEPOS (it));
         }
       else
@@ -5455,8 +5465,7 @@ window_scroll_line_based (window, n, whole, noerror)
   int lose;
   Lisp_Object bolp;
   int startpos;
-  struct position posit;
-  int original_vpos;
+  Lisp_Object original_pos = Qnil;
 
   /* If scrolling screen-fulls, compute the number of lines to
      scroll from the window's height.  */
@@ -5465,11 +5474,24 @@ window_scroll_line_based (window, n, whole, noerror)
 
   startpos = marker_position (w->start);
 
-  posit = *compute_motion (startpos, 0, 0, 0,
-                           PT, ht, 0,
-                           -1, XINT (w->hscroll),
-                           0, w);
-  original_vpos = posit.vpos;
+  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)))
+        {
+          struct position posit
+            = *compute_motion (startpos, 0, 0, 0,
+                               PT, ht, 0,
+                               -1, XINT (w->hscroll),
+                               0, w);
+          window_scroll_preserve_vpos = posit.vpos;
+          window_scroll_preserve_hpos = posit.hpos + XINT (w->hscroll);
+        }
+
+      original_pos = Fcons (make_number (window_scroll_preserve_hpos),
+                            make_number (window_scroll_preserve_vpos));
+    }
 
   XSETFASTINT (tem, PT);
   tem = Fpos_visible_in_window_p (tem, window, Qnil);
@@ -5520,7 +5542,7 @@ window_scroll_line_based (window, n, whole, noerror)
           && (whole || !EQ (Vscroll_preserve_screen_position, Qt)))
         {
           SET_PT_BOTH (pos, pos_byte);
-          Fvertical_motion (make_number (original_vpos), window);
+          Fvertical_motion (original_pos, window);
         }
       /* If we scrolled forward, put point enough lines down
          that it is outside the scroll margin.  */
@@ -5542,7 +5564,7 @@ window_scroll_line_based (window, n, whole, noerror)
           else if (!NILP (Vscroll_preserve_screen_position))
             {
               SET_PT_BOTH (pos, pos_byte);
-              Fvertical_motion (make_number (original_vpos), window);
+              Fvertical_motion (original_pos, window);
             }
           else
             SET_PT (top_margin);
@@ -5567,7 +5589,7 @@ window_scroll_line_based (window, n, whole, noerror)
               if (!NILP (Vscroll_preserve_screen_position))
                 {
                   SET_PT_BOTH (pos, pos_byte);
-                  Fvertical_motion (make_number (original_vpos), window);
+                  Fvertical_motion (original_pos, window);
                 }
               else
                 Fvertical_motion (make_number (-1), window);
@@ -7439,7 +7461,10 @@ syms_of_window ()
   minibuf_selected_window = Qnil;
   staticpro (&minibuf_selected_window);
 
+  window_scroll_pixel_based_preserve_x = -1;
   window_scroll_pixel_based_preserve_y = -1;
+  window_scroll_preserve_hpos = -1;
+  window_scroll_preserve_vpos = -1;
 
   DEFVAR_LISP ("temp-buffer-show-function", &Vtemp_buffer_show_function,
                doc: /* Non-nil means call as function to display a help buffer.
@@ -7640,7 +7665,7 @@ windows horizontally.  A value less than 2 is invalid.  */);
 
   DEFVAR_LISP ("scroll-preserve-screen-position",
                &Vscroll_preserve_screen_position,
-               doc: /* *Controls if scroll commands move point to keep its screen line unchanged.
+               doc: /* *Controls if scroll commands move point to keep its screen position unchanged.
 A value of nil means point does not keep its screen position except
 at the scroll margin or window boundary respectively.
 A value of t means point keeps its screen position if the scroll