Make identifySamplePoints handle compare #3996
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greggman
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src/webgpu/shader/execution/expression/call/builtin/texture_utils.ts
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identifySamplePoints works by doing a binary search filling a texture with black (0,0,0,0) and white (1,1,1,1) texels and then sampling it. Any non-zero results means those white pixels were sampled. This doesn't work for comparisons like textureSampleCompare, textureSampleCompareLevel, and textureGatherCompare because the result of those are 0 or 1 so for example, of the comparison is 'always' then all texels will show up as sampled. So, instead, if the builtin being tested is a comparison we convert the call to the corresponding non-comparsion builtin. * textureSampleCompare -> textureSample * textureSampleCompareLevel -> textureSampleLevel * textureGatherCompare -> textureGather This lets us find the sample points as best we can (it assumes those functions sample the same texels). Once we have the sample point we then want to look up the actual values of the texels and print them out. To do this requires reading the texture back from the GPU. We made the texture ourselves so we could maybe theoretically pass the data we sent to the GPU down to identifySamplePoints but it seems good to get the values from the GPU itself so at least they made a round trip through the GPU When, if it's a comparison, we print out the result of each comparison with that texel. Hopefully this will help us identify why these tests don't pass on some devices.
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identifySamplePoints works by doing a binary search filling a texture with black (0,0,0,0) and white (1,1,1,1) texels and then sampling it. Any non-zero results means those white pixels were sampled.
This doesn't work for comparisons like textureSampleCompare, textureSampleCompareLevel, and textureGatherCompare because the result of those are 0 or 1 so for example, of the comparison is 'always' then all texels will show up as sampled.
So, instead, if the builtin being tested is a comparison we convert the call to the corresponding non-comparsion builtin.
This lets us find the sample points as best we can (it assumes those functions sample the same texels).
Once we have the sample point we then want to look up the actual values of the texels and print them out. To do this requires reading the texture back from the GPU. We made the texture ourselves so we could maybe theoretically pass the data we sent to the GPU down to identifySamplePoints but it seems good to get the values from the GPU itself so at least they made a round trip through the GPU
When, if it's a comparison, we print out the result of each comparison with that texel. Hopefully this will help us identify why these tests don't pass on some devices.