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Yunus Shaikh
2cd0c9107a
The ancillary input's sample number (bits 11:8) was the SampleId builtin in every pixel shader. Vulkan enables sample shading for a shader that uses SampleId, so a shader that reads the sample field or the whole ancillary word ran once per sample on a multisampled draw even when the guest runs it once per pixel (PS_ITER_SAMPLE clear), and FragCoord, and with it POS_X_FLOAT and POS_Y_FLOAT, moved to the sample. The sample number is now SampleId only when the request says the guest iterates the shader, and otherwise 0, the iterated sample number of a pixel the hardware does not iterate. The other inputs that depend on the sample follow where the console evaluates them: - PERSP_SAMPLE and LINEAR_SAMPLE are interpolated with InterpolateAtOffset at sample 0's offset in a shader the guest does not iterate, and in an iterated one at the offset of the host's SampleId, read from a table of the guest's locations, because Vulkan leaves plain barycentrics under sample shading at an implementation-defined position (lavapipe uses the pixel centre). - PERSP_CENTER and LINEAR_CENTER are interpolated at offset 0 in an iterated shader. - POS_X_FLOAT and POS_Y_FLOAT follow SPI_BARYC_CNTL: the centre is floor(FragCoord) + 0.5 under sample shading, a sample position in a shader the guest does not iterate is the centre plus sample 0's offset, and POS_FLOAT_ULC gives the upper-left corner. The offsets need InterpolationFunction (sampleRateShading) and the fragment-shader barycentric path; devices without them keep the host's default positions. The shader disk cache format goes to 39.