HLSL load equivalent in SKSL ?

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Sushanth Rajasankar

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Apr 29, 2021, 6:51:08 PMApr 29
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Hello Skia folks,

I am experimenting with SkiaRuntimeEffects and find myself in a situation where I need to sample exact texels from an input texture. I used skia's sample for this purpose but am running into sampler issues where on some hardware reading the normalized co-ordinate within a texture are resulting in the adjacent texel being read rather than the nearest texel.


I order to avoid this problem, I would like to use the equivalent of HLSL load - which I believe is GLSL texelFetch and use non normalized texel positions. Is there a way to have the equivalent of HLSL load in a SkSL ?

Thanks,
Sushanth


Brian Osman

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May 2, 2021, 9:03:55 AMMay 2
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Not really, no. However: By default, an image shader (created with SkImage::makeShader) will use non-normalized coordinates. Are you making sure to add a half-texel offset when doing your sample, so that the sample locations land in the middle of a texel? If your sample locations are integers (or integers / width,height for normalized coordinates), you will definitely get inconsistent sampling. But if you use integers + 0.5 (or those values / width, height), I would expect precise results on all hardware.

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