Backing store hook.

gistfile1.hs

enableBackingStore dpy win = do
 unmapWindow dpy win
 sync dpy False
 allocaSetWindowAttributes $ \attributes -> do
   set_backing_store attributes always
   changeWindowAttributes dpy win cWBackingStore attributes
 mapWindow dpy win
 sync dpy False

enableBackingStoreHook = 
    ask >>= \w -> liftX $ withDisplay $ \d -> do
         io $ enableBackingStore d w
         return idHook