Clément Foucault
d89fb77d89
This changes the sampling routine to use the method described in "A Simpler and Exact Sampling Routine for the GGXDistribution of Visible Normals" by Eric Heitz. http://jcgt.org/published/0007/04/01/slides.pdf This avoids generating bad rays and thus improve noise level in screen- space reflections / refraction.
60 lines
1.7 KiB
GLSL
60 lines
1.7 KiB
GLSL
#pragma BLENDER_REQUIRE(common_utiltex_lib.glsl)
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#pragma BLENDER_REQUIRE(bsdf_sampling_lib.glsl)
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uniform float sampleCount;
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out vec2 FragColor;
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void main()
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{
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/* Make sure coordinates are covering the whole [0..1] range at texel center. */
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float y = floor(gl_FragCoord.y) / (LUT_SIZE - 1);
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float x = floor(gl_FragCoord.x) / (LUT_SIZE - 1);
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float NV = clamp(1.0 - y * y, 1e-4, 0.9999);
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float a = x * x;
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float a2 = clamp(a * a, 1e-4, 0.9999);
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vec3 V = vec3(sqrt(1.0 - NV * NV), 0.0, NV);
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/* Integrating BRDF */
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float brdf_accum = 0.0;
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float fresnel_accum = 0.0;
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for (float j = 0.0; j < sampleCount; j++) {
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for (float i = 0.0; i < sampleCount; i++) {
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vec3 Xi = (vec3(i, j, 0.0) + 0.5) / sampleCount;
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Xi.yz = vec2(cos(Xi.y * M_2PI), sin(Xi.y * M_2PI));
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/* Microfacet normal */
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vec3 H = sample_ggx(Xi, a, V);
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vec3 L = -reflect(V, H);
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float NL = L.z;
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if (NL > 0.0) {
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float NH = max(H.z, 0.0);
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float VH = max(dot(V, H), 0.0);
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float G1_v = G1_Smith_GGX_opti(NV, a2);
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float G1_l = G1_Smith_GGX_opti(NL, a2);
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/* See G1_Smith_GGX_opti for explanations. */
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float G_smith = 4.0 * NV * NL / (G1_v * G1_l);
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float brdf = (G_smith * VH) / (NH * NV);
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/* Follow maximum specular value for principled bsdf. */
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const float specular = 1.0;
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const float eta = (2.0 / (1.0 - sqrt(0.08 * specular))) - 1.0;
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float fresnel = F_eta(eta, VH);
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float Fc = F_color_blend(eta, fresnel, vec3(0)).r;
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brdf_accum += (1.0 - Fc) * brdf;
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fresnel_accum += Fc * brdf;
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}
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}
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}
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brdf_accum /= sampleCount * sampleCount;
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fresnel_accum /= sampleCount * sampleCount;
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FragColor = vec2(brdf_accum, fresnel_accum);
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}
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