From 6d84fcab760f1aa96eb147ceb749d02dc090ce67 Mon Sep 17 00:00:00 2001
From: Alexander Larsson <alexl@redhat.com>
Date: Mon, 14 Sep 2009 13:38:47 +0200
Subject: [PATCH] Handle expose events moving or resizing windows

When a window is moved or resized from a double-buffered expose handler
we can't really just copy the window region around, as the window
will be overdrawn with the double buffered region when the expose returns.

Instead we remove all regions with outstanding implicit paints from the
region to be copied and just mark this area as invalid to be redrawn
later.

This fixes bug 594880.
---
 gdk/gdkwindow.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 121b81020d..2a44e7f7a9 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -3136,12 +3136,10 @@ append_move_region (GdkWindowObject *impl_window,
 /* Moves bits and update area by dx/dy in impl window.
    Takes ownership of region to avoid copy (because we may change it) */
 static void
-move_region_on_impl (GdkWindowObject *private,
+move_region_on_impl (GdkWindowObject *impl_window,
 		     GdkRegion *region, /* In impl window coords */
 		     int dx, int dy)
 {
-  GdkWindowObject *impl_window;
-
   if ((dx == 0 && dy == 0) ||
       gdk_region_empty (region))
     {
@@ -3149,12 +3147,13 @@ move_region_on_impl (GdkWindowObject *private,
       return;
     }
 
-  impl_window = gdk_window_get_impl_window (private);
+  g_assert (impl_window == gdk_window_get_impl_window (impl_window));
 
   /* Move any old invalid regions in the copy source area by dx/dy */
   if (impl_window->update_area)
     {
       GdkRegion *update_area;
+
       update_area = gdk_region_copy (region);
 
       /* Convert from target to source */
@@ -3176,6 +3175,22 @@ move_region_on_impl (GdkWindowObject *private,
       gdk_region_destroy (update_area);
     }
 
+  /* If we're currently exposing this window, don't copy to this
+     destination, as it will be overdrawn when the expose is done,
+     instead invalidate it and repaint later. */
+  if (impl_window->implicit_paint)
+    {
+      GdkWindowPaint *implicit_paint = impl_window->implicit_paint;
+      GdkRegion *exposing;
+
+      exposing = gdk_region_copy (implicit_paint->region);
+      gdk_region_intersect (exposing, region);
+      gdk_region_subtract (region, exposing);
+
+      impl_window_add_update_area (impl_window, exposing);
+      gdk_region_destroy (exposing);
+    }
+
   if (1) /* Enable flicker free handling of moves. */
     append_move_region (impl_window, region, dx, dy);
   else