Comment 8 for bug 1418081

I think this could be quite serious:

I'm not sure if USC currently works like this but consider:

The greeter starts,
U8 starts and is occludes the greeter.
Around this time the greeter provides a new buffer that doesn't get rendered as it is occluded.
Now there is always an unconsumed buffer in the scene, so compositing never stops.

It is far easier to get scenarios like this on a "desktop" and that is a big waste of resources, on a laptop we don't want to drain batteries like this but on a phone battery this behaviour is deadly.

AFAICS the "query" needs to check only the surfaces /that would be rendered/ and once upon a time we had logic that did this during the compositing pass. (Occlusion is indeed only a special case of surfaces that are not rendered - and it would be good to address the general case.)