WIP: add high-precision GPU trilinear interpolation for 3D LUTs #1794
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This new code path can be enabled by disabling the new default-enabled OPTIMIZATION_NATIVE_GPU_TRILINEAR optimization flag. The existing code path used the GPU's native trilinear texture interpolation function, which, although faster, quantized the lookup coordinates which could cause banding. That's still the default, but full-precision trilinear interpolation can optionally be used instead. Signed-off-by: Nathan Vegdahl <[email protected]>
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This addresses #1763.
The new high-precision code path can be enabled by disabling the new default-enabled OPTIMIZATION_NATIVE_GPU_TRILINEAR optimization flag.
The existing code path used the GPU's native trilinear texture interpolation function, which (although faster) quantized the lookup coordinates and could cause color banding. That's still the default, but now full-precision trilinear interpolation can optionally be used instead.
WIP
This is PR is WIP. It functions, but it's not ready to merge yet:
GetLut3DGPUShaderProgram(). I tried several approaches, but every approach ended up affecting some public API.GPUProcessor::Impl, and then pass them toOp::extractGpuShaderInfo()via a new argument with a default value. Of all the approaches I tried, this seemed to have the lowest impact on both the code and the API.I am very much open to suggestions for a better approach to get the optimization flags to
GetLut3DGPUShaderProgram().Additionally, I still need to add unit tests for the new code path.
Performance
Some initial naive performance tests indicate that the high precision code is notably slower than than GPU-native trilinear interpolation, but about on par with OCIO's tetrahedral interpolation. More testing is needed, however. For example, using higher-res LUTs and testing on a variety of GPUs. I'll update with actual data once I've had a better go at this.