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// Precomputes data for IntegrateLD(). See that function for a detailed description.
#include "ShaderLibrary/Common.hlsl"
#include "ShaderLibrary/ImageBasedLighting.hlsl"
#ifdef SHADER_API_MOBILE
#define MAX_IBL_SAMPLE_CNT 34
#else
#define MAX_IBL_SAMPLE_CNT 89
#endif
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;
float roughness = PerceptualRoughnessToRoughness(MipmapLevelToPerceptualRoughness(mipLevel));
uint sampleCount = GetIBLRuntimeFilterSampleCount(mipLevel);
if (sampleIndex >= sampleCount)
{
output[groupThreadId.xy] = float4(0, 0, 0, 0);
return;
}
float3 V = float3(0, 0, 1);
float NdotV = 1;
float3 localL;
float NdotL, NdotH, LdotH;
const uint validSampleCount = sampleCount;
while (true)
{
uint acceptedSampleCount = 0;
uint shiftedSampleIndex = 0;
for (uint i = 0; i < sampleCount; i++)
{
// We switch to the Golden sequence instead of the Fibonacci sequence
// since the sample count is not guaranteed to be a Fibonacci number.
// TODO: might be interesting to try Mitchell's Poisson disk sampling algorithm.
// In our case, samples would not have disks associated with them, but rather solid angles.
float2 u = Golden2dSeq(i, sampleCount);
SampleGGXDir(u, V, k_identity3x3, roughness, localL, NdotL, NdotH, LdotH, true);
if (NdotL > 0)
{
if (acceptedSampleCount == sampleIndex) shiftedSampleIndex = i;
acceptedSampleCount++;
}
}
if (acceptedSampleCount == validSampleCount)
{
sampleIndex = shiftedSampleIndex;
break;
}
sampleCount++;
}
float2 u = Golden2dSeq(sampleIndex, sampleCount);
SampleGGXDir(u, V, k_identity3x3, roughness, localL, NdotL, NdotH, LdotH, true);
float pdf = 0.25 * D_GGX(NdotH, roughness);
float omegaS = rcp(sampleCount) * rcp(pdf);
output[groupThreadId.xy] = float4(localL, omegaS);
}