RealityKitPostProcessSetupComputePipeline.swift

private func setupComputePipeline(targetTexture: MTLTexture) {
    guard let device = MTLCreateSystemDefaultDevice(),
          let library = device.makeDefaultLibrary(),
          let postProcessingKernel = library.makeFunction(name: "inverseColorKernel"),
          let pipelineState = try? device.makeComputePipelineState(function: postProcessingKernel)
    else {
        assertionFailure()
        return
    }

    computePipelineState = pipelineState

    threadsPerThreadgroup = MTLSize(width: pipelineState.threadExecutionWidth,
                                    height: pipelineState.maxTotalThreadsPerThreadgroup / pipelineState.threadExecutionWidth,
                                    depth: 1)
    threadgroupsPerGrid = MTLSize(width: (targetTexture.width + threadsPerThreadgroup.width - 1) / threadsPerThreadgroup.width,
                                  height: (targetTexture.height + threadsPerThreadgroup.height - 1) / threadsPerThreadgroup.height,
                                  depth: 1)
}