144 lines
3.7 KiB
HLSL
144 lines
3.7 KiB
HLSL
// Copyright (c) 2012-2022 Wojciech Figat. All rights reserved.
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#ifndef __MONTE_CARLO__
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#define __MONTE_CARLO__
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float3 TangentToWorld(float3 vec, float3 tangentZ)
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{
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float3 upVector = abs(tangentZ.z) < 0.999 ? float3(0, 0, 1) : float3(1, 0, 0);
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float3 tangentX = normalize(cross(upVector, tangentZ));
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float3 tangentY = cross(tangentZ, tangentX);
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return tangentX * vec.x + tangentY * vec.y + tangentZ * vec.z;
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}
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uint ReverseBits32(uint bits)
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{
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#if FEATURE_LEVEL >= FEATURE_LEVEL_SM5
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return reversebits(bits);
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#else
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bits = ( bits << 16) | ( bits >> 16);
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bits = ( (bits & 0x00ff00ff) << 8 ) | ( (bits & 0xff00ff00) >> 8 );
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bits = ( (bits & 0x0f0f0f0f) << 4 ) | ( (bits & 0xf0f0f0f0) >> 4 );
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bits = ( (bits & 0x33333333) << 2 ) | ( (bits & 0xcccccccc) >> 2 );
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bits = ( (bits & 0x55555555) << 1 ) | ( (bits & 0xaaaaaaaa) >> 1 );
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return bits;
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#endif
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}
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float2 Hammersley(uint index, uint numSamples, uint2 random)
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{
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float e1 = frac((float)index / numSamples + float(random.x & 0xffff) / (1 << 16));
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float e2 = float(ReverseBits32(index) ^ random.y) * 2.3283064365386963e-10;
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return float2(e1, e2);
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}
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float4 UniformSampleSphere(float2 e)
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{
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float phi = 2 * PI * e.x;
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float cosTheta = 1 - 2 * e.y;
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float sinTheta = sqrt(1 - cosTheta * cosTheta);
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float3 h;
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h.x = sinTheta * cos(phi);
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h.y = sinTheta * sin(phi);
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h.z = cosTheta;
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float pdf = 1.0 / (4 * PI);
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return float4(h, pdf);
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}
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float4 UniformSampleHemisphere(float2 e)
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{
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float phi = 2 * PI * e.x;
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float cosTheta = e.y;
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float sinTheta = sqrt(1 - cosTheta * cosTheta);
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float3 h;
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h.x = sinTheta * cos(phi);
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h.y = sinTheta * sin(phi);
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h.z = cosTheta;
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float pdf = 1.0 / (2 * PI);
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return float4(h, pdf);
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}
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float4 CosineSampleHemisphere(float2 e)
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{
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float phi = 2 * PI * e.x;
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float cosTheta = sqrt(e.y);
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float sinTheta = sqrt(1 - cosTheta * cosTheta);
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float3 h;
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h.x = sinTheta * cos(phi);
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h.y = sinTheta * sin(phi);
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h.z = cosTheta;
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float pdf = cosTheta / PI;
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return float4(h, pdf);
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}
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float4 UniformSampleCone(float2 e, float cosThetaMax)
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{
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float phi = 2 * PI * e.x;
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float cosTheta = lerp(cosThetaMax, 1, e.y);
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float sinTheta = sqrt(1 - cosTheta * cosTheta);
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float3 l;
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l.x = sinTheta * cos(phi);
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l.y = sinTheta * sin(phi);
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l.z = cosTheta;
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float pdf = 1.0 / (2 * PI * (1 - cosThetaMax));
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return float4(l, pdf);
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}
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float4 ImportanceSampleBlinn(float2 e, float roughness)
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{
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float m = roughness * roughness;
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float n = 2 / (m * m) - 2;
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float phi = 2 * PI * e.x;
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float cosTheta = ClampedPow(e.y, 1 / (n + 1));
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float sinTheta = sqrt(1 - cosTheta * cosTheta);
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float3 h;
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h.x = sinTheta * cos(phi);
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h.y = sinTheta * sin(phi);
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h.z = cosTheta;
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float d = (n + 2) / (2 * PI) * ClampedPow(cosTheta, n);
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float pdf = d * cosTheta;
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return float4(h, pdf);
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}
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float4 ImportanceSampleGGX(float2 e, float roughness)
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{
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float m = roughness * roughness;
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float m2 = m * m;
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float phi = 2 * PI * e.x;
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float cosTheta = sqrt((1 - e.y) / (1 + (m2 - 1) * e.y));
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float sinTheta = sqrt(1 - cosTheta * cosTheta);
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float3 h;
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h.x = sinTheta * cos(phi);
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h.y = sinTheta * sin(phi);
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h.z = cosTheta;
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float r = (cosTheta * m2 - cosTheta) * cosTheta + 1;
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float d = m2 / (PI * r * r);
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float pdf = d * cosTheta;
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return float4(h, pdf);
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}
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// Multiple importance sampling power heuristic of two functions with a power of two.
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// [Veach 1997, "Robust Monte Carlo Methods for Light Transport Simulation"]
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float MISWeight(uint number, float PDF, uint otherNumber, float otherPDF)
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{
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float weight = number * PDF;
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float otherWeight = otherNumber * otherPDF;
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return weight * weight / (weight * weight + otherWeight * otherWeight);
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}
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#endif
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