Three PBR 环境光照

• Three框架里面自带的pbr太Magic了,完全不知道出处,不建议看
• 环境光照 diffuse

void RE_IndirectDiffuse_Physical( const in vec3 irradiance, const in GeometricContext geometry, const in PhysicalMaterial material, inout ReflectedLight reflectedLight ) {
    reflectedLight.indirectDiffuse += irradiance * BRDF_Diffuse_Lambert( material.diffuseColor );
}

#define RECIPROCAL_PI 0.3183098861837907
vec3 BRDF_Diffuse_Lambert( const in vec3 diffuseColor ) {
    return RECIPROCAL_PI * diffuseColor;
}

• 环境光照 specular

void RE_IndirectSpecular_Physical( const in vec3 radiance, const in vec3 irradiance, const in vec3 clearcoatRadiance, const in GeometricContext geometry, const in PhysicalMaterial material, inout ReflectedLight reflectedLight) {
    #ifdef CLEARCOAT
        float ccDotNV = saturate( dot( geometry.clearcoatNormal, geometry.viewDir ) );
        reflectedLight.indirectSpecular += clearcoatRadiance * material.clearcoat * BRDF_Specular_GGX_Environment( geometry.viewDir, geometry.clearcoatNormal, vec3( DEFAULT_SPECULAR_COEFFICIENT ), material.clearcoatRoughness );
        float ccDotNL = ccDotNV;
        float clearcoatDHR = material.clearcoat * clearcoatDHRApprox( material.clearcoatRoughness, ccDotNL );
    #else
        float clearcoatDHR = 0.0;
    #endif
    float clearcoatInv = 1.0 - clearcoatDHR;
    vec3 singleScattering = vec3( 0.0 );
    vec3 multiScattering = vec3( 0.0 );
    vec3 cosineWeightedIrradiance = irradiance * RECIPROCAL_PI;
    BRDF_Specular_Multiscattering_Environment( geometry, material.specularColor, material.specularRoughness, singleScattering, multiScattering );
    vec3 diffuse = material.diffuseColor * ( 1.0 - ( singleScattering + multiScattering ) );
    reflectedLight.indirectSpecular += clearcoatInv * radiance * singleScattering;
    reflectedLight.indirectSpecular += multiScattering * cosineWeightedIrradiance;
    reflectedLight.indirectDiffuse += diffuse * cosineWeightedIrradiance;
}

void BRDF_Specular_Multiscattering_Environment( const in GeometricContext geometry, const in vec3 specularColor, const in float roughness, inout vec3 singleScatter, inout vec3 multiScatter ) {
    float dotNV = saturate( dot( geometry.normal, geometry.viewDir ) );
    vec3 F = F_Schlick_RoughnessDependent( specularColor, dotNV, roughness );
    vec2 brdf = integrateSpecularBRDF( dotNV, roughness );
    vec3 FssEss = F * brdf.x + brdf.y;
    float Ess = brdf.x + brdf.y;
    float Ems = 1.0 - Ess;
    vec3 Favg = specularColor + ( 1.0 - specularColor ) * 0.047619;
    vec3 Fms = FssEss * Favg / ( 1.0 - Ems * Favg );
    singleScatter += FssEss;
    multiScatter += Fms * Ems;
}

vec3 F_Schlick_RoughnessDependent( const in vec3 F0, const in float dotNV, const in float roughness ) {
    float fresnel = exp2( ( -5.55473 * dotNV - 6.98316 ) * dotNV );
    vec3 Fr = max( vec3( 1.0 - roughness ), F0 ) - F0;
    return Fr * fresnel + F0;
}