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#pragma BLENDER_REQUIRE(common_utiltex_lib.glsl)
#pragma BLENDER_REQUIRE(bsdf_sampling_lib.glsl)
uniform float sampleCount;
out vec2 FragColor;
void main()
{
/* Make sure coordinates are covering the whole [0..1] range at texel center. */
float y = floor(gl_FragCoord.y) / (LUT_SIZE - 1);
float x = floor(gl_FragCoord.x) / (LUT_SIZE - 1);
float NV = clamp(1.0 - y * y, 1e-4, 0.9999);
float a = x * x;
float a2 = clamp(a * a, 1e-4, 0.9999);
vec3 V = vec3(sqrt(1.0 - NV * NV), 0.0, NV);
/* Integrating BRDF */
float brdf_accum = 0.0;
float fresnel_accum = 0.0;
for (float j = 0.0; j < sampleCount; j++) {
for (float i = 0.0; i < sampleCount; i++) {
vec3 Xi = (vec3(i, j, 0.0) + 0.5) / sampleCount;
Xi.yz = vec2(cos(Xi.y * M_2PI), sin(Xi.y * M_2PI));
vec3 H = sample_ggx(Xi, a2); /* 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);
/* Follow maximum specular value for principled bsdf. */
const float specular = 1.0;
const float eta = (2.0 / (1.0 - sqrt(0.08 * specular))) - 1.0;
float fresnel = F_eta(eta, VH);
float Fc = F_color_blend(eta, fresnel, vec3(0)).r;
brdf_accum += (1.0 - Fc) * brdf;
fresnel_accum += Fc * brdf;
}
}
}
brdf_accum /= sampleCount * sampleCount;
fresnel_accum /= sampleCount * sampleCount;
FragColor = vec2(brdf_accum, fresnel_accum);
}
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