Coverage reduction takes the coverage information for a fragment and converts that to a boolean coverage value for each color sample in each pixel covered by the fragment.
Coverage for each pixel is first extracted from the total fragment coverage mask. This consists of rasterizationSamples unique coverage samples for each pixel in the fragment area, each with a unique sample index. If the fragment only contains a single pixel, coverage for the pixel is equivalent to the fragment coverage.
Color Sample Coverage
Once pixel coverage is determined, coverage for each individual color sample corresponding to that pixel is determined.
The number of rasterizationSamples is identical to the number of samples in the color attachments. A color sample is covered if the pixel coverage sample with the same sample index i is covered.