From c72e93de16f664e07460723f74f33d306f753bd7 Mon Sep 17 00:00:00 2001
From: Alexander Larsson <alexl@redhat.com>
Date: Wed, 4 Feb 2009 16:23:15 +0100
Subject: [PATCH] Workaround X11 clipping bug

It turns out that XCopyArea handling of obscured source regions is
buggy. It clears the destination area even outside the GC clip
region. We work around this for the pixmap->window case as that
can happen in gtk+ and is easy to work around.

X Bug report at:
http://lists.freedesktop.org/archives/xorg/2009-February/043318.html
---
 gdk/x11/gdkdrawable-x11.c | 43 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 40 insertions(+), 3 deletions(-)

diff --git a/gdk/x11/gdkdrawable-x11.c b/gdk/x11/gdkdrawable-x11.c
index 2e53041bb2..e6ea4f1853 100644
--- a/gdk/x11/gdkdrawable-x11.c
+++ b/gdk/x11/gdkdrawable-x11.c
@@ -634,13 +634,50 @@ gdk_x11_draw_drawable (GdkDrawable *drawable,
 
   if (GDK_IS_DRAWABLE_IMPL_X11 (src))
     src_impl = GDK_DRAWABLE_IMPL_X11 (src);
+  else if (GDK_IS_WINDOW (src))
+    src_impl = GDK_DRAWABLE_IMPL_X11(((GdkWindowObject *)src)->impl);
   else
-    src_impl = NULL;
+    src_impl = GDK_DRAWABLE_IMPL_X11(((GdkPixmapObject *)src)->impl);
+
+  if (GDK_IS_WINDOW_IMPL_X11 (impl) &&
+      GDK_IS_PIXMAP_IMPL_X11 (src_impl))
+    {
+      GdkPixmapImplX11 *src_pixmap = GDK_PIXMAP_IMPL_X11 (src_impl);
+      /* Work around an Xserver bug where non-visible areas from
+       * a pixmap to a window will clear the window background
+       * in destination areas that are supposed to be clipped out.
+       * This is a problem with client side windows as this means
+       * things may draw outside the virtual windows. This could
+       * also happen for window to window copies, but I don't
+       * think we generate any calls like that.
+       *
+       * See: 
+       * http://lists.freedesktop.org/archives/xorg/2009-February/043318.html
+       */
+      if (xsrc < 0)
+	{
+	  width += xsrc;
+	  xdest -= xsrc;
+	  xsrc = 0;
+	}
+      
+      if (ysrc < 0)
+	{
+	  height += ysrc;
+	  ydest -= ysrc;
+	  ysrc = 0;
+	}
+
+      if (xsrc + width > src_pixmap->width)
+	width = src_pixmap->width - xsrc;
+      if (ysrc + height > src_pixmap->height)
+	height = src_pixmap->height - ysrc;
+    }
   
   if (src_depth == 1)
     {
       XCopyArea (GDK_SCREEN_XDISPLAY (impl->screen),
-                 src_impl ? src_impl->xid : GDK_DRAWABLE_XID (src),
+                 src_impl->xid,
 		 impl->xid,
 		 GDK_GC_GET_XGC (gc),
 		 xsrc, ysrc,
@@ -650,7 +687,7 @@ gdk_x11_draw_drawable (GdkDrawable *drawable,
   else if (dest_depth != 0 && src_depth == dest_depth)
     {
       XCopyArea (GDK_SCREEN_XDISPLAY (impl->screen),
-                 src_impl ? src_impl->xid : GDK_DRAWABLE_XID (src),
+                 src_impl->xid,
 		 impl->xid,
 		 GDK_GC_GET_XGC (gc),
 		 xsrc, ysrc,