lib-sheen.glsl

Public Functions: pbrComputeSheen

Import from library

import lib-defines.glsl
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import lib-defines.glsl

All engine parameters useful for sheen.

//: param custom {
 //:   "group": "Base Surface",
 //:   "label": "Enable sheen",
 //:   "default": false,
 //:   "asm": "sheen",
 //:   "description": "<html><head/><body><p>Simulates the effect of microscopic fibers or fuzz on the surface.<br/><b>Please note</b>: The following channel needs to be present for this parameter to have an effect: <b>Sheen opacity</b>. Optionally, the following channels provide additional control: <b>Sheen color</b> and <b>Sheen roughness</b>.</p></body></html>"
 //: }
 uniform_specialization bool sheenEnabled;
 //: param auto channel_sheenopacity
 uniform SamplerSparse sheenOpacity_tex;
 //: param auto channel_sheencolor
 uniform SamplerSparse sheenColor_tex;
 //: param auto channel_sheenroughness
 uniform SamplerSparse sheenRoughness_tex;
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//: param custom {
 //:   "group": "Base Surface",
 //:   "label": "Enable sheen",
 //:   "default": false,
 //:   "asm": "sheen",
 //:   "description": "<html><head/><body><p>Simulates the effect of microscopic fibers or fuzz on the surface.<br/><b>Please note</b>: The following channel needs to be present for this parameter to have an effect: <b>Sheen opacity</b>. Optionally, the following channels provide additional control: <b>Sheen color</b> and <b>Sheen roughness</b>.</p></body></html>"
 //: }
 uniform_specialization bool sheenEnabled;
 //: param auto channel_sheenopacity
 uniform SamplerSparse sheenOpacity_tex;
 //: param auto channel_sheencolor
 uniform SamplerSparse sheenColor_tex;
 //: param auto channel_sheenroughness
 uniform SamplerSparse sheenRoughness_tex;

Import from library

import lib-pbr.glsl
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import lib-pbr.glsl

Compute the sheen BRDF contribution for importance sampling.

vec3 sheen_contrib(float ndh, float ndl, float ndv, vec3 Ks, float roughness)
 {
    float ndh2 = ndh*ndh;
    float ndl2 = ndl*ndl;
    float ndv2 = ndv*ndv;
    float r2 = roughness*roughness;
 
    // TODO: move the D component out, to the importance sampling.
    float t = 1.0 - ndh2 + ndh2/r2;
    float Pi_D = 1.0 / (roughness * t * t);
 
    float Li = sqrt(1.0 - ndl2 + r2*ndl2) / ndl;
    float Lo = sqrt(1.0 - ndv2 + r2*ndv2) / ndv;
    float G = (1.0 - exp(-(Li + Lo))) / (Li + Lo);
 
    // This is the contribution when using importance sampling with uniform
    // sample distribution. This means sheen_contrib = sheen_brdf / (1/(2*Pi))
    // ndl is omitted since it cancels out with the ndl outside the BRDF.
    return Ks * ((2.0 * Pi_D * G / ndv) * 0.5);
 }
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vec3 sheen_contrib(float ndh, float ndl, float ndv, vec3 Ks, float roughness)
 {
    float ndh2 = ndh*ndh;
    float ndl2 = ndl*ndl;
    float ndv2 = ndv*ndv;
    float r2 = roughness*roughness;
 
    // TODO: move the D component out, to the importance sampling.
    float t = 1.0 - ndh2 + ndh2/r2;
    float Pi_D = 1.0 / (roughness * t * t);
 
    float Li = sqrt(1.0 - ndl2 + r2*ndl2) / ndl;
    float Lo = sqrt(1.0 - ndv2 + r2*ndv2) / ndv;
    float G = (1.0 - exp(-(Li + Lo))) / (Li + Lo);
 
    // This is the contribution when using importance sampling with uniform
    // sample distribution. This means sheen_contrib = sheen_brdf / (1/(2*Pi))
    // ndl is omitted since it cancels out with the ndl outside the BRDF.
    return Ks * ((2.0 * Pi_D * G / ndv) * 0.5);
 }

Compute the microfacets sheen specular reflection to the viewer's eye.

vec3 pbrComputeSheen(LocalVectors vectors, vec3 specColor, float roughness)
 {
    vec3 radiance = vec3(0.0);
    float ndv = dot(vectors.eye, vectors.normal);
    roughness = max(1e-3, roughness);
    vec3 envT = worldToEnvSpace(vectors.tangent);
    vec3 envB = worldToEnvSpace(vectors.bitangent);
    vec3 envN = worldToEnvSpace(vectors.normal);
    vec3 envE = worldToEnvSpace(vectors.eye);
    vec3 envVertexNormal = worldToEnvSpace(vectors.vertexNormal);
 
    for(int i=0; i<nbSamples; ++i)
    {
        vec2 Xi = fibonacci2D(i, nbSamples);
        vec3 Ln = uniformSample(Xi, envT, envB, envN);
        vec3 Hn = normalize(Ln + envE);
        float fade = horizonFading(dot(envVertexNormal, Ln), horizonFade);
 
        float ndl = dot(envN, Ln);
        if (ndl > 0.0 && ndv > 0.0) {
            ndl = max( 1e-8, ndl );
            float vdh = max(1e-8, dot(envE, Hn));
            float ndh = max(1e-8, dot(envN, Hn));
            float lodS = computeLOD(Ln, 0.5 * M_INV_PI);
            radiance += fade * envSample(Ln, lodS) * sheen_contrib(ndh, ndl, ndv, specColor, roughness);
        }
    }
    radiance /= float(nbSamples);
 
    return radiance;
 }
 
 
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vec3 pbrComputeSheen(LocalVectors vectors, vec3 specColor, float roughness)
 {
    vec3 radiance = vec3(0.0);
    float ndv = dot(vectors.eye, vectors.normal);
    roughness = max(1e-3, roughness);
    vec3 envT = worldToEnvSpace(vectors.tangent);
    vec3 envB = worldToEnvSpace(vectors.bitangent);
    vec3 envN = worldToEnvSpace(vectors.normal);
    vec3 envE = worldToEnvSpace(vectors.eye);
    vec3 envVertexNormal = worldToEnvSpace(vectors.vertexNormal);
 
    for(int i=0; i<nbSamples; ++i)
    {
        vec2 Xi = fibonacci2D(i, nbSamples);
        vec3 Ln = uniformSample(Xi, envT, envB, envN);
        vec3 Hn = normalize(Ln + envE);
        float fade = horizonFading(dot(envVertexNormal, Ln), horizonFade);
 
        float ndl = dot(envN, Ln);
        if (ndl > 0.0 && ndv > 0.0) {
            ndl = max( 1e-8, ndl );
            float vdh = max(1e-8, dot(envE, Hn));
            float ndh = max(1e-8, dot(envN, Hn));
            float lodS = computeLOD(Ln, 0.5 * M_INV_PI);
            radiance += fade * envSample(Ln, lodS) * sheen_contrib(ndh, ndl, ndv, specColor, roughness);
        }
    }
    radiance /= float(nbSamples);
 
    return radiance;
 }

lib-sampler

lib-sparse

Last updated 10/3/2024

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