You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
133 lines
4.4 KiB
133 lines
4.4 KiB
/*******************************************************************************************
|
|
*
|
|
* BRDF LUT Generation - Bidirectional reflectance distribution function fragment shader
|
|
*
|
|
* REF: https://github.com/HectorMF/BRDFGenerator
|
|
*
|
|
* Copyright (c) 2017 Victor Fisac
|
|
*
|
|
**********************************************************************************************/
|
|
|
|
#version 330
|
|
|
|
|
|
// Input vertex attributes (from vertex shader)
|
|
in vec2 fragTexCoord;
|
|
|
|
// Constant values
|
|
const float PI = 3.14159265359;
|
|
const uint MAX_SAMPLES = 1024u;
|
|
|
|
// Output fragment color
|
|
out vec4 finalColor;
|
|
|
|
vec2 Hammersley(uint i, uint N);
|
|
float RadicalInverseVdC(uint bits);
|
|
float GeometrySchlickGGX(float NdotV, float roughness);
|
|
float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness);
|
|
vec3 ImportanceSampleGGX(vec2 Xi, vec3 N, float roughness);
|
|
vec2 IntegrateBRDF(float NdotV, float roughness);
|
|
|
|
float RadicalInverseVdC(uint bits)
|
|
{
|
|
bits = (bits << 16u) | (bits >> 16u);
|
|
bits = ((bits & 0x55555555u) << 1u) | ((bits & 0xAAAAAAAAu) >> 1u);
|
|
bits = ((bits & 0x33333333u) << 2u) | ((bits & 0xCCCCCCCCu) >> 2u);
|
|
bits = ((bits & 0x0F0F0F0Fu) << 4u) | ((bits & 0xF0F0F0F0u) >> 4u);
|
|
bits = ((bits & 0x00FF00FFu) << 8u) | ((bits & 0xFF00FF00u) >> 8u);
|
|
return float(bits) * 2.3283064365386963e-10; // / 0x100000000
|
|
}
|
|
|
|
// Compute Hammersley coordinates
|
|
vec2 Hammersley(uint i, uint N)
|
|
{
|
|
return vec2(float(i)/float(N), RadicalInverseVdC(i));
|
|
}
|
|
|
|
// Integrate number of importance samples for (roughness and NoV)
|
|
vec3 ImportanceSampleGGX(vec2 Xi, vec3 N, float roughness)
|
|
{
|
|
float a = roughness*roughness;
|
|
float phi = 2.0 * PI * Xi.x;
|
|
float cosTheta = sqrt((1.0 - Xi.y)/(1.0 + (a*a - 1.0)*Xi.y));
|
|
float sinTheta = sqrt(1.0 - cosTheta*cosTheta);
|
|
|
|
// Transform from spherical coordinates to cartesian coordinates (halfway vector)
|
|
vec3 H = vec3(cos(phi)*sinTheta, sin(phi)*sinTheta, cosTheta);
|
|
|
|
// Transform from tangent space H vector to world space sample vector
|
|
vec3 up = ((abs(N.z) < 0.999) ? vec3(0.0, 0.0, 1.0) : vec3(1.0, 0.0, 0.0));
|
|
vec3 tangent = normalize(cross(up, N));
|
|
vec3 bitangent = cross(N, tangent);
|
|
vec3 sampleVec = tangent*H.x + bitangent*H.y + N*H.z;
|
|
|
|
return normalize(sampleVec);
|
|
}
|
|
|
|
float GeometrySchlickGGX(float NdotV, float roughness)
|
|
{
|
|
// For IBL k is calculated different
|
|
float k = (roughness*roughness)/2.0;
|
|
|
|
float nom = NdotV;
|
|
float denom = NdotV*(1.0 - k) + k;
|
|
|
|
return nom/denom;
|
|
}
|
|
|
|
// Compute the geometry term for the BRDF given roughness squared, NoV, NoL
|
|
float GeometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
|
|
{
|
|
float NdotV = max(dot(N, V), 0.0);
|
|
float NdotL = max(dot(N, L), 0.0);
|
|
float ggx2 = GeometrySchlickGGX(NdotV, roughness);
|
|
float ggx1 = GeometrySchlickGGX(NdotL, roughness);
|
|
|
|
return ggx1*ggx2;
|
|
}
|
|
|
|
vec2 IntegrateBRDF(float NdotV, float roughness)
|
|
{
|
|
float A = 0.0;
|
|
float B = 0.0;
|
|
vec3 V = vec3(sqrt(1.0 - NdotV*NdotV), 0.0, NdotV);
|
|
vec3 N = vec3(0.0, 0.0, 1.0);
|
|
|
|
for (uint i = 0u; i < MAX_SAMPLES; i++)
|
|
{
|
|
// Generate a sample vector that's biased towards the preferred alignment direction (importance sampling)
|
|
|
|
vec2 Xi = Hammersley(i, MAX_SAMPLES); // Compute a Hammersely coordinate
|
|
vec3 H = ImportanceSampleGGX(Xi, N, roughness); // Integrate number of importance samples for (roughness and NoV)
|
|
vec3 L = normalize(2.0*dot(V, H)*H - V); // Compute reflection vector L
|
|
|
|
float NdotL = max(L.z, 0.0); // Compute normal dot light
|
|
float NdotH = max(H.z, 0.0); // Compute normal dot half
|
|
float VdotH = max(dot(V, H), 0.0); // Compute view dot half
|
|
|
|
if (NdotL > 0.0)
|
|
{
|
|
float G = GeometrySmith(N, V, L, roughness); // Compute the geometry term for the BRDF given roughness squared, NoV, NoL
|
|
float GVis = (G*VdotH)/(NdotH*NdotV); // Compute the visibility term given G, VoH, NoH, NoV, NoL
|
|
float Fc = pow(1.0 - VdotH, 5.0); // Compute the fresnel term given VoH
|
|
|
|
A += (1.0 - Fc)*GVis; // Sum the result given fresnel, geometry, visibility
|
|
B += Fc*GVis;
|
|
}
|
|
}
|
|
|
|
// Calculate brdf average sample
|
|
A /= float(MAX_SAMPLES);
|
|
B /= float(MAX_SAMPLES);
|
|
|
|
return vec2(A, B);
|
|
}
|
|
|
|
void main()
|
|
{
|
|
// Calculate brdf based on texture coordinates
|
|
vec2 brdf = IntegrateBRDF(fragTexCoord.x, fragTexCoord.y);
|
|
|
|
// Calculate final fragment color
|
|
finalColor = vec4(brdf.r, brdf.g, 0.0, 1.0);
|
|
}
|