Fix background update race, speed up rendering!

lib/Phi/X11.hs

@@ -208,8 +208,9 @@ updatePanels dispvar = do
       let screen = defaultScreen disp
           visual = defaultVisual disp screen
       
-      buffer <- liftIO $ withDimension area $ Util.createXlibSurface disp pixmap visual
+      xbuffer <- liftIO $ withDimension area $ Util.createXlibSurface disp pixmap visual
       
+      liftIO $ (withDimension area $ withSimilarSurface xbuffer ContentColor) $ \buffer -> do
         renderWith buffer $ do
           withPatternForSurface rootImage $ \pattern -> do
             save
@@ -218,8 +219,12 @@ updatePanels dispvar = do
             paint
             restore
           Widget.renderWidgets layoutedWidgets $ panelScreenArea panel
+        renderWith xbuffer $ do
+          withPatternForSurface buffer $ \pattern -> do
+            setSource pattern
+            paint
       
-      surfaceFinish buffer
+      surfaceFinish xbuffer
       
       -- copy buffer to window
       liftIO $ do
@@ -266,7 +271,12 @@ updateRootImage disp = do
   
   bg <- gets phiRootImage
   
-  when (pixmap /= 0) $ do
+  case pixmap of 
+    0 -> do
+      renderWith bg $ do
+        setSourceRGB 0 0 0
+        paint
+    _ -> do
       rootSurface <- liftIO $ Util.createXlibSurface disp pixmap visual (fromIntegral rootWidth) (fromIntegral rootHeight)
       
       renderWith bg $ withPatternForSurface rootSurface $ \pattern -> do