Fix scrolling under scroll-preserve-screen-position on TTY

* src/window.c (window_scroll_line_based): When setting point to
preserve screen coordinates, don't let cursor enter either of the
two scroll margins.  (Bug#22395)

diff --git a/src/window.c b/src/window.c
index 1a75342471f8f5cadb18b3544ba2dd0eca8e0e12..2eacc3a2647fe585a2e4a4ae8faa88edc6906861 100644 (file)
--- a/src/window.c
+++ b/src/window.c
@@ -5212,6 +5212,7 @@ window_scroll_line_based (Lisp_Object window, int n, bool whole, bool noerror)
       w->force_start = true;
 
       if (!NILP (Vscroll_preserve_screen_position)
+         && this_scroll_margin == 0
          && (whole || !EQ (Vscroll_preserve_screen_position, Qt)))
        {
          SET_PT_BOTH (pos, pos_byte);
@@ -5237,8 +5238,16 @@ window_scroll_line_based (Lisp_Object window, int n, bool whole, bool noerror)
                         marker_byte_position (opoint_marker));
          else if (!NILP (Vscroll_preserve_screen_position))
            {
+             int nlines = window_scroll_preserve_vpos;
+
              SET_PT_BOTH (pos, pos_byte);
-             Fvertical_motion (original_pos, window, Qnil);
+             if (window_scroll_preserve_vpos < this_scroll_margin)
+               nlines = this_scroll_margin;
+             else if (window_scroll_preserve_vpos
+                      >= w->total_lines - this_scroll_margin)
+               nlines = w->total_lines - this_scroll_margin - 1;
+             Fvertical_motion (Fcons (make_number (window_scroll_preserve_hpos),
+                                      make_number (nlines)), window, Qnil);
            }
          else
            SET_PT (top_margin);
@@ -5264,8 +5273,16 @@ window_scroll_line_based (Lisp_Object window, int n, bool whole, bool noerror)
            {
              if (!NILP (Vscroll_preserve_screen_position))
                {
+                 int nlines = window_scroll_preserve_vpos;
+
                  SET_PT_BOTH (pos, pos_byte);
-                 Fvertical_motion (original_pos, window, Qnil);
+                 if (window_scroll_preserve_vpos < this_scroll_margin)
+                   nlines = this_scroll_margin;
+                 else if (window_scroll_preserve_vpos
+                          >= ht - this_scroll_margin)
+                   nlines = ht - this_scroll_margin - 1;
+                 Fvertical_motion (Fcons (make_number (window_scroll_preserve_hpos),
+                                          make_number (nlines)), window, Qnil);
                }
              else
                Fvertical_motion (make_number (-1), window, Qnil);