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out vec4 FragColor;
void main() {
vec3 N, T, B, V;
float NV = ( 1.0 - (clamp(gl_FragCoord.y / BRDF_LUT_SIZE, 1e-4, 0.9999)));
float sqrtRoughness = clamp(gl_FragCoord.x / BRDF_LUT_SIZE, 1e-4, 0.9999);
float a = sqrtRoughness * sqrtRoughness;
float a2 = a * a;
N = vec3(0.0, 0.0, 1.0);
T = vec3(1.0, 0.0, 0.0);
B = vec3(0.0, 1.0, 0.0);
V = vec3(sqrt(1.0 - NV * NV), 0.0, NV);
setup_noise();
/* Integrating BRDF */
float brdf_accum = 0.0;
float fresnel_accum = 0.0;
for (float i = 0; i < sampleCount; i++) {
vec3 H = sample_ggx(i, a2, N, T, B); /* Microfacet normal */
vec3 L = -reflect(V, H);
float NL = L.z;
if (NL > 0.0) {
float NH = max(H.z, 0.0);
float VH = max(dot(V, H), 0.0);
float G1_v = G1_Smith_GGX(NV, a2);
float G1_l = G1_Smith_GGX(NL, a2);
float G_smith = 4.0 * NV * NL / (G1_v * G1_l); /* See G1_Smith_GGX for explanations. */
float brdf = (G_smith * VH) / (NH * NV);
float Fc = pow(1.0 - VH, 5.0);
brdf_accum += (1.0 - Fc) * brdf;
fresnel_accum += Fc * brdf;
}
}
brdf_accum /= sampleCount;
fresnel_accum /= sampleCount;
FragColor = vec4(brdf_accum, fresnel_accum, 0.0, 1.0);
}
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