GLTF Material Anisotropy extension

Custom extension to support anisotropy factor and anisotropic rotation/direction map in GLTF/GLB

Blender Addon

Export anisotropy factor and texture from PBS materials supported by cycles

To install, put the plugin directory in the addons folder of your blender installation.

For Mac its /Applications/Blender.app/Contents/Resources/2.92/scripts/addons

Threejs Import

Import with custom GLTF loader extension. Adds the parameters and loaded texture to material userData. Change extension name if needed.

Register:

gltfLoader.register((p)=>new GLTFMaterialsAnisotropyExtension(p))

Shaders

Functions for adding anisotropy in Physical shader in threejs. Code taken mostly from filament. (Links in code)

Sample threejs shader patching (for onBeforeCompile).

 const rotMap: ITexture | undefined = material.materialObject.userData?.anisotropyRotationMap
 const bsdfs = glsl`
    #include <bsdfs>
    //#if ANISOTROPY_ENABLED
    ${randomHelpers}
    ${anisotropyBsdf}
` + (rotMap ? getTexelDecoding('anisotropyRotationMap', rotMap, renderer.capabilities.isWebGL2) : '')
shader.fragmentShader = shader.fragmentShader.replace('#include <bsdfs>', bsdfs)

shader.fragmentShader = shader.fragmentShader.replace('#include <lights_fragment_begin>', ShaderChunk.lights_fragment_begin)

shader.fragmentShader = shader.fragmentShader
    .replace('IncidentLight directLight;', anisotropyTBN + 'IncidentLight directLight;')
    .replaceAll('RE_Direct( directLight, geometry, material, reflectedLight )',
        'RE_Direct( directLight, geometry, material, reflectedLight, anisotropicT, anisotropicB )')

// eslint-disable-next-line @typescript-eslint/naming-convention
const lights_physical_pars_fragment = ShaderChunk.lights_physical_pars_fragment
    .replace('void RE_Direct_Physical( const in IncidentLight directLight, const in GeometricContext geometry, const in PhysicalMaterial material, inout ReflectedLight reflectedLight ) {',
        'void RE_Direct_Physical( const in IncidentLight directLight, const in GeometricContext geometry, const in PhysicalMaterial material, inout ReflectedLight reflectedLight, const in vec3 anisotropicT, const in vec3 anisotropicB ) {')
    .replace('BRDF_GGX( directLight.direction, geometry.viewDir, geometry.normal, material.specularColor, material.specularF90, material.roughness )',
        'BRDF_GGX_Anisotropy( directLight.direction, geometry.viewDir, geometry.normal, material.specularColor, material.specularF90, material.roughness, anisotropicT, anisotropicB )')
shader.fragmentShader = shader.fragmentShader.replace('#include <lights_physical_pars_fragment>', lights_physical_pars_fragment)

// eslint-disable-next-line @typescript-eslint/naming-convention
const lights_fragment_maps = glsl`
    #if defined( USE_ENVMAP )
    vec3 anisotropyBentNormal = indirectAnisotropyBentNormal(geometry.normal, geometry.viewDir, material.roughness, anisotropicT, anisotropicB);
    #endif
` + ShaderChunk.lights_fragment_maps
    .replace('getIBLIrradiance( geometry.normal )',
        'getIBLIrradiance( anisotropyBentNormal )')
    .replace('getIBLRadiance( geometry.viewDir, geometry.normal, material.roughness )',
        'getIBLRadiance( geometry.viewDir, anisotropyBentNormal, material.roughness )')
shader.fragmentShader = shader.fragmentShader.replace('#include <lights_fragment_maps>', lights_fragment_maps)

;(shader as any).vertexUvs = true
;(shader as any).vertexTangents = true