Occlusion culling based on coverage buffer

Occlusion culling based on coverage buffer.

1. Downscale depth target.
2. Readback to CPU, Readback latency will be serveral frames( It will be depends on graphics command queue counts. ).
3. Reprojection with current frame camera matrix(Bottom-left depth image above the image).
4. Loop each object
5. CPU Rasterization of AABB or OBB.
6. Visibility Z test(Transparent red color quad is culled object OOB above the image).

Pros: If framerate is not fast enough then it will get depth that did not project correctlly.

This technique came from crytek.