anisotropy.glsllib

// Copyright (C) 2026 The Qt Company Ltd.

// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only

#ifndef ANISOTROPY_GLSLLIB

#define ANISOTROPY_GLSLLIB 1

#include "bsdf.glsllib"

#include "principledMaterialFresnel.glsllib" // qt_schlick

#ifndef M_PI

#define M_PI 3.14159265359

#endif

// KHR_materials_anisotropy: replaces the GGX distribution and visibility terms

// Fallback tangent for meshes without one (Duff et al. 2017)

vec3 qt_orthonormalTangent(in vec3 normal)

    float s = normal.z >= 0.0 ? 1.0 : -1.0;

    float a = -1.0 / (s + normal.z);

    float b = normal.x * normal.y * a;

    return vec3(1.0 + s * normal.x * normal.x * a, s * b, -s * normal.x);

float qt_D_GGX_anisotropic(in float NdotH, in float TdotH, in float BdotH, in float at, in float ab)

    float a2 = at * ab;

    vec3 f = vec3(ab * TdotH, at * BdotH, a2 * NdotH);

    float w2 = a2 / dot(f, f);

    return a2 * w2 * w2 / M_PI;

// Includes the 1/(4 NdotL NdotV) term, like qt_V_GGX

float qt_V_GGX_anisotropic(in float NdotL, in float NdotV, in float BdotV, in float TdotV,

                           in float TdotL, in float BdotL, in float at, in float ab)

    float GGXV = NdotL * length(vec3(at * TdotV, ab * BdotV, NdotV));

    float GGXL = NdotV * length(vec3(at * TdotL, ab * BdotL, NdotL));

    return clamp(0.5 / (GGXV + GGXL), 0.0, 1.0);

vec4 qt_specularAnisotropicGGXBSDF(in vec3 normal, in vec3 tangent, in vec3 bitangent,

                                   in vec3 L, in vec3 V, in vec3 lightSpecular,

                                   in vec3 F0, in vec3 F90, in float at, in float ab)

    float cNdotL = max(0.0, dot(normal, L));

    float cNdotV = max(0.0, dot(normal, V));

    vec3 H = normalize(V + L);

    float cLdotH = max(0.0, dot(L, H));

    float cNdotH = max(0.001, dot(normal, H)); // arguments for the distribution must not be 0

    float GGX_D = qt_D_GGX_anisotropic(cNdotH, dot(tangent, H), dot(bitangent, H), at, ab);

    float GGX_V = qt_V_GGX_anisotropic(cNdotL, cNdotV, dot(bitangent, V), dot(tangent, V),

                                       dot(tangent, L), dot(bitangent, L), at, ab);

    float cLdotH5 = qt_schlick(cLdotH);

    vec3 F = mix(vec3(cLdotH5), F90, F0);

    return vec4(cNdotL * GGX_D * F * GGX_V * lightSpecular, 1.0);

// Bent normal for image based lighting, as recommended by the extension

vec3 qt_anisotropicBentNormal(in vec3 normal, in vec3 viewDir, in vec3 bitangent,

                              in float strength, in float roughness)

    vec3 bent = cross(bitangent, viewDir);

    bent = normalize(cross(bent, bitangent));

    // pow(1 - strength * (1 - roughness), 4)

    float a = 1.0 - strength * (1.0 - roughness);

    a = a * a;

    a = a * a;

    return normalize(mix(bent, normal, a));

#endif // ANISOTROPY_GLSLLIB