42 lines
1.8 KiB
GLSL
42 lines
1.8 KiB
GLSL
/**
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* Evalutes lit materials with the subsurface shading model. This model is a
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* combination of a BRDF (the same used in shading_model_standard.fs, refer to that
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* file for more information) and of an approximated BTDF to simulate subsurface
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* scattering. The BTDF itself is not physically based and does not represent a
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* correct interpretation of transmission events.
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*/
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vec3 surfaceShading(const PixelParams pixel, const Light light, float occlusion) {
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vec3 h = normalize(shading_view + light.l);
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float NoL = light.NoL;
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float NoH = saturate(dot(shading_normal, h));
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float LoH = saturate(dot(light.l, h));
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vec3 Fr = vec3(0.0);
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if (NoL > 0.0) {
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// specular BRDF
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float D = distribution(pixel.roughness, NoH, h);
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float V = visibility(pixel.roughness, shading_NoV, NoL);
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vec3 F = fresnel(pixel.f0, LoH);
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Fr = (D * V) * F * pixel.energyCompensation;
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}
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// diffuse BRDF
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vec3 Fd = pixel.diffuseColor * diffuse(pixel.roughness, shading_NoV, NoL, LoH);
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// NoL does not apply to transmitted light
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vec3 color = (Fd + Fr) * (NoL * occlusion);
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// subsurface scattering
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// Use a spherical gaussian approximation of pow() for forwardScattering
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// We could include distortion by adding shading_normal * distortion to light.l
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float scatterVoH = saturate(dot(shading_view, -light.l));
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float forwardScatter = exp2(scatterVoH * pixel.subsurfacePower - pixel.subsurfacePower);
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float backScatter = saturate(NoL * pixel.thickness + (1.0 - pixel.thickness)) * 0.5;
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float subsurface = mix(backScatter, 1.0, forwardScatter) * (1.0 - pixel.thickness);
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color += pixel.subsurfaceColor * (subsurface * Fd_Lambert());
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// TODO: apply occlusion to the transmitted light
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return (color * light.colorIntensity.rgb) * (light.colorIntensity.w * light.attenuation);
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}
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