Merge lp:~vanvugt/compiz/fix-1014986 into lp:compiz/0.9.8

[Daniel van Vugt]

Don't waste CPU looping through and looking at all the windows if you're
rendering an output that has no damage on it. (LP: #1014986)

Don't waste CPU looping through and looking at all the windows if you're
rendering an output that has no damage on it. (LP: #1014986)

The point at which we do the isEmpty check is a code path that is only reachable if PAINT_SCREEN_REGION_MASK and not PAINT_SCREEN_TRANSFORMED_MASK.

I did try to do the check at the top of glPaintOutput instead. But that caused problems with plugins like rotate which don't set PAINT_SCREEN_TRANSFORMED_MASK early enough. So windows would sometimes freeze during cube rotation.

Checking for isEmpty right before priv->paintOutputRegion seems safest.

[Sam Spilsbury (smspillaz)]

Yep that's fine. We should always invoke a paint in the transformed case anyways.

review: Approve

=== modified file 'plugins/opengl/src/paint.cpp'
--- plugins/opengl/src/paint.cpp	2012-08-14 06:33:22 +0000
+++ plugins/opengl/src/paint.cpp	2012-08-24 08:43:20 +0000
@@ -590,7 +590,8 @@
 
 	sTransform.toScreenSpace (output, -DEFAULT_Z_CAMERA);
 
-	priv->paintOutputRegion (sTransform, region, output, mask);
+	if (!region.isEmpty ())
+	    priv->paintOutputRegion (sTransform, region, output, mask);
 
 	return true;
     }