I have question about the working of alpha to coverage. Coverage value specifies that which samples of a pixels are covered by the primitive. with alpha to coverage, we AND alpha value with coverage value of the pixel to determine the final coverage.
Now Superbible specifies that “if 66% of the pixel is covered by the primitive and alpha value is 40% then final coverage value would be 60 x 40 % which is 25% and for 8 sample buffer, 2 samples will be covered.” But how does it work at sample level.? and how does it determine which samples to cover out of 8?
if the coverage is a bit field for each sample then how does AND operation is performed for each sample ?
and how does it determine which samples to cover out of 8?
The spec is rather unambiguous about its ambiguities on this matter:
In short: implementation dependent, but hopefully not stupid. I’m surprised the Superbible didn’t bother to even say “the exact algorithm is implementation-dependent.”