gl_SampleMaskIn

is a fragment language that indicates the set of samples covered by the primitive generating the fragment during multisample rasterization. It has a sample bit set if and only if the sample is considered covered for this fragment shader invocation. Bit B of mask corresponds to sample 32 * M + B . The array has ceil ( s / 32) elements where s is the maximum number of color samples supported by the implementation.

gl_SampleMask , gl_SampleID , gl_SamplePosition , gl_FragCoord

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