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// Precomputes data for IntegrateLD(). See that function for a detailed description.
#include "Common.hlsl"
#include "ImageBasedLighting.hlsl"
#define MAX_IBL_SAMPLE_CNT 89
RWTexture2D<float4> output; // [MAX_SAMPLE_CNT x UNITY_SPECCUBE_LOD_STEPS]
#pragma kernel ComputeGgxIblSampleData
[numthreads(MAX_IBL_SAMPLE_CNT, UNITY_SPECCUBE_LOD_STEPS, 1)]
void ComputeGgxIblSampleData(uint3 groupThreadId : SV_GroupThreadID)
{
uint sampleIndex = groupThreadId.x;
uint mipLevel = groupThreadId.y + 1;
uint sampleCount = GetIBLRuntimeFilterSampleCount(mipLevel);
if (sampleIndex >= sampleCount)
{
output[groupThreadId.xy] = float4(0, 0, 0, 0);
return;
}
float perceptualRoughness = MipmapLevelToPerceptualRoughness(mipLevel);
float roughness = PerceptualRoughnessToRoughness(perceptualRoughness);
float bias = 0.5 * roughness;
float2 u = Fibonacci2d(sampleIndex, sampleCount);
u.x = lerp(u.x, 0, bias);
float3 localL;
float NdotL, NdotH, VdotH;
SampleGGXDir(u, float3(0, 0, 1), k_identity3x3, roughness, localL, NdotL, NdotH, VdotH, true);
if (NdotL <= 0)
{
// We are not supposed to generate wasteful samples.
output[groupThreadId.xy] = float4(0, 0, 0, 0);
return;
}
float pdf = D_GGX(NdotH, roughness) * 0.25;
float omegaS = rcp(sampleCount * pdf);
output[groupThreadId.xy] = float4(localL, omegaS);
}