[gtk+] gdkwindow: Avoid re-setting the opaque region if it doesn't change

[Rui Matos <rtcm src gnome org>]

commit e702ee8fa68283ac68cc4b8338c413ce8c881bc2
Author: Rui Matos <tiagomatos gmail com>
Date:   Fri Aug 18 12:01:54 2017 +0200

    gdkwindow: Avoid re-setting the opaque region if it doesn't change
    
    This avoids, at least, needless chatter with the compositor and the X
    server in X11's case.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=786469

 gdk/gdkinternals.h |    2 ++
 gdk/gdkwindow.c    |   11 +++++++++++
 2 files changed, 13 insertions(+), 0 deletions(-)
---
diff --git a/gdk/gdkinternals.h b/gdk/gdkinternals.h
index 537741b..7e17aee 100644
--- a/gdk/gdkinternals.h
+++ b/gdk/gdkinternals.h
@@ -285,6 +285,8 @@ struct _GdkWindow
   GdkFrameClock *frame_clock; /* NULL to use from parent or default */
 
   GdkDrawingContext *drawing_context;
+
+  cairo_region_t *opaque_region;
 };
 
 #define GDK_WINDOW_TYPE(d) ((((GdkWindow *)(d)))->window_type)
diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 010a27e..09d136c 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -404,6 +404,9 @@ gdk_window_finalize (GObject *object)
 
   g_clear_object (&window->display);
 
+  if (window->opaque_region)
+    cairo_region_destroy (window->opaque_region);
+
   G_OBJECT_CLASS (gdk_window_parent_class)->finalize (object);
 }
 
@@ -8142,6 +8145,14 @@ gdk_window_set_opaque_region (GdkWindow      *window,
   g_return_if_fail (GDK_IS_WINDOW (window));
   g_return_if_fail (!GDK_WINDOW_DESTROYED (window));
 
+  if (cairo_region_equal (window->opaque_region, region))
+    return;
+
+  g_clear_pointer (&window->opaque_region, cairo_region_destroy);
+
+  if (region != NULL)
+    window->opaque_region = cairo_region_reference (region);
+
   impl_class = GDK_WINDOW_IMPL_GET_CLASS (window->impl);
 
   if (impl_class->set_opaque_region)