(x_scroll_bar_create): Initialize bar->redraw_needed_p.

(XTset_vertical_scroll_bar): Redraw scroll bar if bar->redraw_needed_p
is set even without positional changes.
(x_scroll_bar_clear): Set bar->redraw_needed_p.

1 files changed, 26 insertions, 6 deletions

diff --git a/src/macterm.c b/src/macterm.c
index 82bd085a9b..b110f0372f 100644
--- a/src/macterm.c
+++ b/src/macterm.c
@@ -4998,6 +4998,7 @@ x_scroll_bar_create (w, top, left, width, height, disp_top, disp_height)
   XSETINT (bar->start, 0);
   XSETINT (bar->end, 0);
   bar->dragging = Qnil;
+  bar->redraw_needed_p = Qnil;
 #ifdef USE_TOOLKIT_SCROLL_BARS
   bar->track_top = Qnil;
   bar->track_height = Qnil;
@@ -5193,10 +5194,20 @@ XTset_vertical_scroll_bar (w, portion, whole, position)
       BLOCK_INPUT;
 
       /* If already correctly positioned, do nothing.  */
-      if (!(XINT (bar->left) == sb_left
-	    && XINT (bar->top) == top
-	    && XINT (bar->width) == sb_width
-	    && XINT (bar->height) == height))
+      if (XINT (bar->left) == sb_left
+	  && XINT (bar->top) == top
+	  && XINT (bar->width) == sb_width
+	  && XINT (bar->height) == height)
+	{
+	  if (!NILP (bar->redraw_needed_p))
+	    {
+#if USE_CG_DRAWING
+	      mac_prepare_for_quickdraw (f);
+#endif
+	      Draw1Control (SCROLL_BAR_CONTROL_HANDLE (bar));
+	    }
+	}
+      else
 	{
 	  /* Since toolkit scroll bars are smaller than the space reserved
 	     for them on the frame, we have to clear "under" them.  */
@@ -5229,6 +5240,8 @@ XTset_vertical_scroll_bar (w, portion, whole, position)
       UNBLOCK_INPUT;
     }
 
+  bar->redraw_needed_p = Qnil;
+
 #ifdef USE_TOOLKIT_SCROLL_BARS
   if (NILP (bar->track_top))
     {
@@ -5581,8 +5594,15 @@ void
 x_scroll_bar_clear (f)
      FRAME_PTR f;
 {
-  XTcondemn_scroll_bars (f);
-  XTjudge_scroll_bars (f);
+  Lisp_Object bar;
+
+  /* We can have scroll bars even if this is 0,
+     if we just turned off scroll bar mode.
+     But in that case we should not clear them.  */
+  if (FRAME_HAS_VERTICAL_SCROLL_BARS (f))
+    for (bar = FRAME_SCROLL_BARS (f); VECTORP (bar);
+	 bar = XSCROLL_BAR (bar)->next)
+      XSCROLL_BAR (bar)->redraw_needed_p = Qt;
 }