113 lines
3.6 KiB
GLSL
113 lines
3.6 KiB
GLSL
#version 330 core
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out vec2 FragColor;
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in vec2 TexCoords;
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const float PI = 3.14159265359;
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// ----------------------------------------------------------------------------
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// http://holger.dammertz.org/stuff/notes_HammersleyOnHemisphere.html
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// efficient VanDerCorpus calculation.
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float RadicalInverse_VdC(uint bits)
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{
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bits = (bits << 16u) | (bits >> 16u);
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bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
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bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
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bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
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bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
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return float(bits) * 2.3283064365386963e-10; // / 0x100000000
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}
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// ----------------------------------------------------------------------------
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vec2 Hammersley(uint i, uint N)
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{
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return vec2(float(i)/float(N), RadicalInverse_VdC(i));
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}
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// ----------------------------------------------------------------------------
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vec3 ImportanceSampleGGX(vec2 Xi, vec3 N, float roughness)
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{
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float a = roughness*roughness;
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float phi = 2.0 * PI * Xi.x;
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float cosTheta = sqrt((1.0 - Xi.y) / (1.0 + (a*a - 1.0) * Xi.y));
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float sinTheta = sqrt(1.0 - cosTheta*cosTheta);
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// from spherical coordinates to cartesian coordinates - halfway vector
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vec3 H;
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H.x = cos(phi) * sinTheta;
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H.y = sin(phi) * sinTheta;
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H.z = cosTheta;
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// from tangent-space H vector to world-space sample vector
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vec3 up = abs(N.z) < 0.999 ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0);
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vec3 tangent = normalize(cross(up, N));
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vec3 bitangent = cross(N, tangent);
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vec3 sampleVec = tangent * H.x + bitangent * H.y + N * H.z;
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return normalize(sampleVec);
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}
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// ----------------------------------------------------------------------------
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float GeometrySchlickGGX(float NdotV, float roughness)
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{
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// note that we use a different k for IBL
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float a = roughness;
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float k = (a * a) / 2.0;
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float nom = NdotV;
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float denom = NdotV * (1.0 - k) + k;
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return nom / denom;
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}
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// ----------------------------------------------------------------------------
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float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
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{
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float NdotV = max(dot(N, V), 0.0);
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float NdotL = max(dot(N, L), 0.0);
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float ggx2 = GeometrySchlickGGX(NdotV, roughness);
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float ggx1 = GeometrySchlickGGX(NdotL, roughness);
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return ggx1 * ggx2;
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}
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// ----------------------------------------------------------------------------
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vec2 IntegrateBRDF(float NdotV, float roughness)
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{
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vec3 V;
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V.x = sqrt(1.0 - NdotV*NdotV);
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V.y = 0.0;
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V.z = NdotV;
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float A = 0.0;
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float B = 0.0;
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vec3 N = vec3(0.0, 0.0, 1.0);
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const uint SAMPLE_COUNT = 1024u;
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for(uint i = 0u; i < SAMPLE_COUNT; ++i)
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{
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// generates a sample vector that's biased towards the
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// preferred alignment direction (importance sampling).
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vec2 Xi = Hammersley(i, SAMPLE_COUNT);
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vec3 H = ImportanceSampleGGX(Xi, N, roughness);
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vec3 L = normalize(2.0 * dot(V, H) * H - V);
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float NdotL = max(L.z, 0.0);
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float NdotH = max(H.z, 0.0);
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float VdotH = max(dot(V, H), 0.0);
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if(NdotL > 0.0)
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{
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float G = GeometrySmith(N, V, L, roughness);
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float G_Vis = (G * VdotH) / (NdotH * NdotV);
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float Fc = pow(1.0 - VdotH, 5.0);
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A += (1.0 - Fc) * G_Vis;
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B += Fc * G_Vis;
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}
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}
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A /= float(SAMPLE_COUNT);
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B /= float(SAMPLE_COUNT);
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return vec2(A, B);
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}
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// ----------------------------------------------------------------------------
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void main()
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{
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vec2 integratedBRDF = IntegrateBRDF(TexCoords.x, TexCoords.y);
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FragColor = integratedBRDF;
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} |