[mutter] screen: Fetch the COW window up-front

[Jasper St. Pierre <jstpierre src gnome org>]

commit 463b50e7463417197a0af5dc646365f24cbb08f6
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Thu Jul 10 14:03:03 2014 -0400

    screen: Fetch the COW window up-front
    
    XGetCompositeOverlayWindow is a round trip to the X server. We shouldn't
    be doing it on every MapWindow.

 src/compositor/compositor.c |    2 +-
 src/core/screen-private.h   |    2 ++
 src/core/screen.c           |    3 +++
 src/x11/window-x11.c        |    2 +-
 4 files changed, 7 insertions(+), 2 deletions(-)
---
diff --git a/src/compositor/compositor.c b/src/compositor/compositor.c
index 7481fa5..b67b5fa 100644
--- a/src/compositor/compositor.c
+++ b/src/compositor/compositor.c
@@ -157,7 +157,7 @@ get_output_window (MetaCompositor *compositor)
   unsigned char mask_bits[XIMaskLen (XI_LASTEVENT)] = { 0 };
   XIEventMask mask = { XIAllMasterDevices, sizeof (mask_bits), mask_bits };
 
-  output = XCompositeGetOverlayWindow (xdisplay, DefaultRootWindow (xdisplay));
+  output = compositor->display->screen->composite_overlay_window;
 
   XISetMask (mask.mask, XI_KeyPress);
   XISetMask (mask.mask, XI_KeyRelease);
diff --git a/src/core/screen-private.h b/src/core/screen-private.h
index 766af4b..44edd93 100644
--- a/src/core/screen-private.h
+++ b/src/core/screen-private.h
@@ -119,6 +119,8 @@ struct _MetaScreen
    * and restack them below a guard window. When using a compositor
    * this allows us to provide live previews of unmapped windows */
   Window guard_window;
+
+  Window composite_overlay_window;
 };
 
 struct _MetaScreenClass
diff --git a/src/core/screen.c b/src/core/screen.c
index fbd3e7d..dd720c0 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -45,6 +45,7 @@
 #include "meta-cursor-tracker-private.h"
 
 #include <X11/extensions/Xinerama.h>
+#include <X11/extensions/Xcomposite.h>
 
 #include <X11/Xatom.h>
 #include <locale.h>
@@ -700,6 +701,8 @@ meta_screen_new (MetaDisplay *display,
   screen->starting_corner = META_SCREEN_TOPLEFT;
   screen->guard_window = None;
 
+  screen->composite_overlay_window = XCompositeGetOverlayWindow (xdisplay, xroot);
+
   reload_monitor_infos (screen);
 
   meta_screen_set_cursor (screen, META_CURSOR_DEFAULT);
diff --git a/src/x11/window-x11.c b/src/x11/window-x11.c
index 29976d2..45b04d2 100644
--- a/src/x11/window-x11.c
+++ b/src/x11/window-x11.c
@@ -2942,7 +2942,7 @@ is_our_xwindow (MetaDisplay       *display,
   if (xwindow == screen->guard_window)
     return TRUE;
 
-  if (xwindow == XCompositeGetOverlayWindow (display->xdisplay, screen->xroot))
+  if (xwindow == screen->composite_overlay_window)
     return TRUE;
 
   /* Any windows created via meta_create_offscreen_window */