140 lines
4 KiB
GLSL
140 lines
4 KiB
GLSL
/*******************************************************************************************
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*
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* rPBR [shader] - Bidirectional reflectance distribution function fragment shader
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*
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* Copyright (c) 2017 Victor Fisac
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*
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**********************************************************************************************/
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#version 330
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#define MAX_SAMPLES 1024u
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# Input vertex attributes (from vertex shader)
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in vec2 fragTexCoord
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# Constant values
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const float PI = 3.14159265359
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# Output fragment color
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out vec4 finalColor
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float DistributionGGX(vec3 N, vec3 H, float roughness)
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float RadicalInverse_VdC(uint bits)
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vec2 Hammersley(uint i, uint N)
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vec3 ImportanceSampleGGX(vec2 Xi, vec3 N, float roughness)
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float GeometrySchlickGGX(float NdotV, float roughness)
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float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
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vec2 IntegrateBRDF(float NdotV, float roughness)
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float DistributionGGX(vec3 N, vec3 H, float roughness)
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[
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float a = roughness*roughness
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float a2 = a*a
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float NdotH = max(dot(N, H), 0.0)
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float NdotH2 = NdotH*NdotH
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float nom = a2
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float denom = (NdotH2*(a2 - 1.0) + 1.0)
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denom = PI*denom*denom
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return nom/denom
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]
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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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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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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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# Transform from spherical coordinates to cartesian coordinates (halfway vector)
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vec3 H = vec3(cos(phi)*sinTheta, sin(phi)*sinTheta, cosTheta)
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# Transform 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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float GeometrySchlickGGX(float NdotV, float roughness)
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[
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# For IBL k is calculated different
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float k = (roughness*roughness)/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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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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vec2 IntegrateBRDF(float NdotV, float roughness)
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[
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vec3 V = vec3(sqrt(1.0 - NdotV*NdotV), 0.0, 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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for(uint i = 0u i < MAX_SAMPLES i++)
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[
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# Generate a sample vector that's biased towards the preferred alignment direction (importance sampling)
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vec2 Xi = Hammersley(i, MAX_SAMPLES)
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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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# Calculate brdf average sample
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A /= float(MAX_SAMPLES)
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B /= float(MAX_SAMPLES)
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return vec2(A, B)
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]
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void main()
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[
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# Calculate brdf based on texture coordinates
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vec2 brdf = IntegrateBRDF(fragTexCoord.x, fragTexCoord.y)
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# Calculate final fragment color
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finalColor = vec4(brdf.r, brdf.g, 0.0, 1.0)
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]
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