From 42941eba8a52de5d48136c41e57f792b4e5f0571 Mon Sep 17 00:00:00 2001
From: Jacopo De Simoi <wilderkde@gmail.com>
Date: Thu, 28 Apr 2011 11:34:50 -0400
Subject: [PATCH] kwin: Fix the clip intersection code (XRender)

Do not process windows if the clip region does not
intersect the window region
---
 scene_xrender.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scene_xrender.cpp b/scene_xrender.cpp
index 228e71cba6..13e9b72f85 100644
--- a/scene_xrender.cpp
+++ b/scene_xrender.cpp
@@ -613,6 +613,12 @@ void SceneXrender::Window::performPaint(int mask, QRegion region, WindowPaintDat
         if ( mask & PAINT_WINDOW_TRANSLUCENT && opaque )
             return; // Only painting translucent and window is opaque
         }*/
+    // Intersect the clip region with the rectangle the window occupies on the screen
+    if (!(mask & (PAINT_WINDOW_TRANSFORMED | PAINT_SCREEN_TRANSFORMED)))
+        region &= toplevel->visibleRect();
+
+    if (region.isEmpty())
+        return;
     Picture pic = picture(); // get XRender picture
     if (pic == None)   // The render format can be null for GL and/or Xv visuals
         return;