[gtk+] window: copy back window surface data when the implicit paint is flushed

[Alexander Larsson <alexl src gnome org>]

commit 8f4f7faa119e18eaf212e661efc542c0a4266b20
Author: Cosimo Cecchi <cosimoc gnome org>
Date:   Tue Dec 6 18:41:33 2011 -0500

    window: copy back window surface data when the implicit paint is flushed
    
    When an implicit paint is flushed during expose, e.g. because a
    non-double buffered widget is painting, make sure to copy the existing
    data from the window surface we rendered before flushing back to the
    paint surface, instead of using an empty base.
    Code was already handling that (and said so in the comment), but only
    when no implicit paint was used at all, and not in the case when it's
    flushed mid-expose.

 gdk/gdkwindow.c |   30 +++++++++++++++++-------------
 1 files changed, 17 insertions(+), 13 deletions(-)
---
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index db47512..efdddbe 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -2959,21 +2959,25 @@ gdk_window_begin_paint_region (GdkWindow       *window,
                                                           gdk_window_get_content (window),
 			                                  MAX (clip_box.width, 1),
                                                           MAX (clip_box.height, 1));
+    }
 
-      /* Normally alpha backgrounded client side windows are composited on the implicit paint
-	 by being drawn in back to front order. However, if implicit paints are not used, for
-	 instance if it was flushed due to a non-double-buffered paint in the middle of the
-	 expose we need to copy in the existing data here. */
-      if (!gdk_window_has_impl (window) && window->has_alpha_background)
-	{
-	  cairo_t *cr = cairo_create (paint->surface);
-	  gdk_cairo_set_source_window (cr, impl_window,
-				       - (window->abs_x + clip_box.x),
-				       - (window->abs_y + clip_box.y));
-	  cairo_paint (cr);
-	  cairo_destroy (cr);
-	}
+  /* Normally alpha backgrounded client side windows are composited on the implicit paint
+     by being drawn in back to front order. However, if implicit paints are not used, for
+     instance if it was flushed due to a non-double-buffered paint in the middle of the
+     expose we need to copy in the existing data here. */
+  if (!gdk_window_has_impl (window) &&
+      window->has_alpha_background &&
+      (!implicit_paint ||
+       (implicit_paint && implicit_paint->flushed)))
+    {
+      cairo_t *cr = cairo_create (paint->surface);
+      gdk_cairo_set_source_window (cr, impl_window,
+                                   - (window->abs_x + clip_box.x),
+                                   - (window->abs_y + clip_box.y));
+      cairo_paint (cr);
+      cairo_destroy (cr);
     }
+
   cairo_surface_set_device_offset (paint->surface, -clip_box.x, -clip_box.y);
 
   for (list = window->paint_stack; list != NULL; list = list->next)