Code review comment for lp:~vanvugt/mir/unocclude

I'm not entirely sure now how much benefit occlusion detection could provide in the non-blocking world. You lose the benefit of limiting client CPU/GPU usage because you have to force unblocking of clients under the new model.

There's only one benefit remaining. That is to reduce the number of renderables that get thrown at the renderer. But OpenGL has always, by design, optimized out offscreen textures and geometry anyway. So that just gives you one obscure uncommon benefit: A small renderable hidden behind a larger one does not get its texture uploaded on that frame. However this benefit only applies to software surfaces where there is an actual "upload", and is irrelevant if the foreground is fullscreen because that's already optimized by bypass. The benefit of occlusion detection in the non-blocking world seems negligible.