romainguy

float D_GGX_Anisotropic(float at, float ab, float ToH, float BoH, float NoH) {
    // Burley 2012, "Physically-Based Shading at Disney"
    float a2 = at * ab;
    vec3 d = vec3(ab * ToH, at * BoH, a2 * NoH);
    return saturateMediump(a2 * sq(a2 / dot(d, d)) * (1.0 / PI));
}

float V_SmithGGXCorrelated_Anisotropic(float at, float ab, float ToV, float BoV,
        float ToL, float BoL, float NoV, float NoL) {
    // Heitz 2014, "Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs"

romainguy

    vec3  anisotropyDirection = pixel.anisotropy >= 0.0 ? pixel.anisotropicB : pixel.anisotropicT;
    vec3  anisotropicTangent  = cross(anisotropyDirection, shading_view);
    vec3  anisotropicNormal   = cross(anisotropicTangent, anisotropyDirection);
    float bendFactor          = abs(pixel.anisotropy) * saturate(5.0 * pixel.roughness);
    vec3  bentNormal          = normalize(mix(shading_normal, anisotropicNormal, bendFactor));

    vec3 r = reflect(-shading_view, bentNormal);

romainguy

// From https://github.com/google/filament
float D_GGX(float linearRoughness, float NoH, const vec3 h) {
    // Walter et al. 2007, "Microfacet Models for Refraction through Rough Surfaces"

    // In mediump, there are two problems computing 1.0 - NoH^2
    // 1) 1.0 - NoH^2 suffers floating point cancellation when NoH^2 is close to 1 (highlights)
    // 2) NoH doesn't have enough precision around 1.0
    // Both problem can be fixed by computing 1-NoH^2 in highp and providing NoH in highp as well

    // However, we can do better using Lagrange's identity:

romainguy

// Uniform array of 4 vec3 for SH environment lighting
// Computed from "Ditch River" (http://www.hdrlabs.com/sibl/archive.html)
static const vec3 sphericalHarmonics[4] = {
        {  0.754554516862612,  0.748542953903366,  0.790921515418539 },
        { -0.083856548007422,  0.092533500963210,  0.322764661032516 },
        {  0.308152705331738,  0.366796330467391,  0.466698181299906 },
        { -0.188884931542396, -0.277402551592231, -0.377844212327557 }
};

// Fragment shader, "n" is the normal at the shading point