GLTFLoader.js

( function () {

    class GLTFLoader extends THREE.Loader {

        constructor( manager ) {

            super( manager );
            this.dracoLoader = null;
            this.ktx2Loader = null;
            this.meshoptDecoder = null;
            this.pluginCallbacks = [];
            this.register( function ( parser ) {

                return new GLTFMaterialsClearcoatExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFTextureBasisUExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFTextureWebPExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMaterialsSheenExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMaterialsTransmissionExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMaterialsVolumeExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMaterialsIorExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMaterialsEmissiveStrengthExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMaterialsSpecularExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMaterialsIridescenceExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFLightsExtension( parser );

            } );
            this.register( function ( parser ) {

                return new GLTFMeshoptCompression( parser );

            } );

        }

        load( url, onLoad, onProgress, onError ) {

            const scope = this;
            let resourcePath;

            if ( this.resourcePath !== '' ) {

                resourcePath = this.resourcePath;

            } else if ( this.path !== '' ) {

                resourcePath = this.path;

            } else {

                resourcePath = THREE.LoaderUtils.extractUrlBase( url );

            } // Tells the LoadingManager to track an extra item, which resolves after
            // the model is fully loaded. This means the count of items loaded will
            // be incorrect, but ensures manager.onLoad() does not fire early.


            this.manager.itemStart( url );

            const _onError = function ( e ) {

                if ( onError ) {

                    onError( e );

                } else {

                    console.error( e );

                }

                scope.manager.itemError( url );
                scope.manager.itemEnd( url );

            };

            const loader = new THREE.FileLoader( this.manager );
            loader.setPath( this.path );
            loader.setResponseType( 'arraybuffer' );
            loader.setRequestHeader( this.requestHeader );
            loader.setWithCredentials( this.withCredentials );
            loader.load( url, function ( data ) {

                try {

                    scope.parse( data, resourcePath, function ( gltf ) {

                        onLoad( gltf );
                        scope.manager.itemEnd( url );

                    }, _onError );

                } catch ( e ) {

                    _onError( e );

                }

            }, onProgress, _onError );

        }

        setDRACOLoader( dracoLoader ) {

            this.dracoLoader = dracoLoader;
            return this;

        }

        setDDSLoader() {

            throw new Error( 'THREE.GLTFLoader: "MSFT_texture_dds" no longer supported. Please update to "KHR_texture_basisu".' );

        }

        setKTX2Loader( ktx2Loader ) {

            this.ktx2Loader = ktx2Loader;
            return this;

        }

        setMeshoptDecoder( meshoptDecoder ) {

            this.meshoptDecoder = meshoptDecoder;
            return this;

        }

        register( callback ) {

            if ( this.pluginCallbacks.indexOf( callback ) === - 1 ) {

                this.pluginCallbacks.push( callback );

            }

            return this;

        }

        unregister( callback ) {

            if ( this.pluginCallbacks.indexOf( callback ) !== - 1 ) {

                this.pluginCallbacks.splice( this.pluginCallbacks.indexOf( callback ), 1 );

            }

            return this;

        }

        parse( data, path, onLoad, onError ) {

            let content;
            const extensions = {};
            const plugins = {};

            if ( typeof data === 'string' ) {

                content = data;

            } else {

                const magic = THREE.LoaderUtils.decodeText( new Uint8Array( data, 0, 4 ) );

                if ( magic === BINARY_EXTENSION_HEADER_MAGIC ) {

                    try {

                        extensions[ EXTENSIONS.KHR_BINARY_GLTF ] = new GLTFBinaryExtension( data );

                    } catch ( error ) {

                        if ( onError ) onError( error );
                        return;

                    }

                    content = extensions[ EXTENSIONS.KHR_BINARY_GLTF ].content;

                } else {

                    content = THREE.LoaderUtils.decodeText( new Uint8Array( data ) );

                }

            }

            const json = JSON.parse( content );

            if ( json.asset === undefined || json.asset.version[ 0 ] < 2 ) {

                if ( onError ) onError( new Error( 'THREE.GLTFLoader: Unsupported asset. glTF versions >=2.0 are supported.' ) );
                return;

            }

            const parser = new GLTFParser( json, {
                path: path || this.resourcePath || '',
                crossOrigin: this.crossOrigin,
                requestHeader: this.requestHeader,
                manager: this.manager,
                ktx2Loader: this.ktx2Loader,
                meshoptDecoder: this.meshoptDecoder
            } );
            parser.fileLoader.setRequestHeader( this.requestHeader );

            for ( let i = 0; i < this.pluginCallbacks.length; i ++ ) {

                const plugin = this.pluginCallbacks[ i ]( parser );
                plugins[ plugin.name ] = plugin; // Workaround to avoid determining as unknown extension
                // in addUnknownExtensionsToUserData().
                // Remove this workaround if we move all the existing
                // extension handlers to plugin system

                extensions[ plugin.name ] = true;

            }

            if ( json.extensionsUsed ) {

                for ( let i = 0; i < json.extensionsUsed.length; ++ i ) {

                    const extensionName = json.extensionsUsed[ i ];
                    const extensionsRequired = json.extensionsRequired || [];

                    switch ( extensionName ) {

                    case EXTENSIONS.KHR_MATERIALS_UNLIT:
                        extensions[ extensionName ] = new GLTFMaterialsUnlitExtension();
                        break;

                    case EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS:
                        extensions[ extensionName ] = new GLTFMaterialsPbrSpecularGlossinessExtension();
                        break;

                    case EXTENSIONS.KHR_DRACO_MESH_COMPRESSION:
                        extensions[ extensionName ] = new GLTFDracoMeshCompressionExtension( json, this.dracoLoader );
                        break;

                    case EXTENSIONS.KHR_TEXTURE_TRANSFORM:
                        extensions[ extensionName ] = new GLTFTextureTransformExtension();
                        break;

                    case EXTENSIONS.KHR_MESH_QUANTIZATION:
                        extensions[ extensionName ] = new GLTFMeshQuantizationExtension();
                        break;

                    default:
                        if ( extensionsRequired.indexOf( extensionName ) >= 0 && plugins[ extensionName ] === undefined ) {

                            console.warn( 'THREE.GLTFLoader: Unknown extension "' + extensionName + '".' );

                        }

                    }

                }

            }

            parser.setExtensions( extensions );
            parser.setPlugins( plugins );
            parser.parse( onLoad, onError );

        }

        parseAsync( data, path ) {

            const scope = this;
            return new Promise( function ( resolve, reject ) {

                scope.parse( data, path, resolve, reject );

            } );

        }

    }
    /* GLTFREGISTRY */


    function GLTFRegistry() {

        let objects = {};
        return {
            get: function ( key ) {

                return objects[ key ];

            },
            add: function ( key, object ) {

                objects[ key ] = object;

            },
            remove: function ( key ) {

                delete objects[ key ];

            },
            removeAll: function () {

                objects = {};

            }
        };

    }
    /*********************************/

    /********** EXTENSIONS ***********/

    /*********************************/


    const EXTENSIONS = {
        KHR_BINARY_GLTF: 'KHR_binary_glTF',
        KHR_DRACO_MESH_COMPRESSION: 'KHR_draco_mesh_compression',
        KHR_LIGHTS_PUNCTUAL: 'KHR_lights_punctual',
        KHR_MATERIALS_CLEARCOAT: 'KHR_materials_clearcoat',
        KHR_MATERIALS_IOR: 'KHR_materials_ior',
        KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS: 'KHR_materials_pbrSpecularGlossiness',
        KHR_MATERIALS_SHEEN: 'KHR_materials_sheen',
        KHR_MATERIALS_SPECULAR: 'KHR_materials_specular',
        KHR_MATERIALS_TRANSMISSION: 'KHR_materials_transmission',
        KHR_MATERIALS_IRIDESCENCE: 'KHR_materials_iridescence',
        KHR_MATERIALS_UNLIT: 'KHR_materials_unlit',
        KHR_MATERIALS_VOLUME: 'KHR_materials_volume',
        KHR_TEXTURE_BASISU: 'KHR_texture_basisu',
        KHR_TEXTURE_TRANSFORM: 'KHR_texture_transform',
        KHR_MESH_QUANTIZATION: 'KHR_mesh_quantization',
        KHR_MATERIALS_EMISSIVE_STRENGTH: 'KHR_materials_emissive_strength',
        EXT_TEXTURE_WEBP: 'EXT_texture_webp',
        EXT_MESHOPT_COMPRESSION: 'EXT_meshopt_compression'
    };
    /**
     * Punctual Lights Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_lights_punctual
     */

    class GLTFLightsExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_LIGHTS_PUNCTUAL; // THREE.Object3D instance caches

            this.cache = {
                refs: {},
                uses: {}
            };

        }

        _markDefs() {

            const parser = this.parser;
            const nodeDefs = this.parser.json.nodes || [];

            for ( let nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex ++ ) {

                const nodeDef = nodeDefs[ nodeIndex ];

                if ( nodeDef.extensions && nodeDef.extensions[ this.name ] && nodeDef.extensions[ this.name ].light !== undefined ) {

                    parser._addNodeRef( this.cache, nodeDef.extensions[ this.name ].light );

                }

            }

        }

        _loadLight( lightIndex ) {

            const parser = this.parser;
            const cacheKey = 'light:' + lightIndex;
            let dependency = parser.cache.get( cacheKey );
            if ( dependency ) return dependency;
            const json = parser.json;
            const extensions = json.extensions && json.extensions[ this.name ] || {};
            const lightDefs = extensions.lights || [];
            const lightDef = lightDefs[ lightIndex ];
            let lightNode;
            const color = new THREE.Color( 0xffffff );
            if ( lightDef.color !== undefined ) color.fromArray( lightDef.color );
            const range = lightDef.range !== undefined ? lightDef.range : 0;

            switch ( lightDef.type ) {

            case 'directional':
                lightNode = new THREE.DirectionalLight( color );
                lightNode.target.position.set( 0, 0, - 1 );
                lightNode.add( lightNode.target );
                break;

            case 'point':
                lightNode = new THREE.PointLight( color );
                lightNode.distance = range;
                break;

            case 'spot':
                lightNode = new THREE.SpotLight( color );
                lightNode.distance = range; // Handle spotlight properties.

                lightDef.spot = lightDef.spot || {};
                lightDef.spot.innerConeAngle = lightDef.spot.innerConeAngle !== undefined ? lightDef.spot.innerConeAngle : 0;
                lightDef.spot.outerConeAngle = lightDef.spot.outerConeAngle !== undefined ? lightDef.spot.outerConeAngle : Math.PI / 4.0;
                lightNode.angle = lightDef.spot.outerConeAngle;
                lightNode.penumbra = 1.0 - lightDef.spot.innerConeAngle / lightDef.spot.outerConeAngle;
                lightNode.target.position.set( 0, 0, - 1 );
                lightNode.add( lightNode.target );
                break;

            default:
                throw new Error( 'THREE.GLTFLoader: Unexpected light type: ' + lightDef.type );

            } // Some lights (e.g. spot) default to a position other than the origin. Reset the position
            // here, because node-level parsing will only override position if explicitly specified.


            lightNode.position.set( 0, 0, 0 );
            lightNode.decay = 2;
            if ( lightDef.intensity !== undefined ) lightNode.intensity = lightDef.intensity;
            lightNode.name = parser.createUniqueName( lightDef.name || 'light_' + lightIndex );
            dependency = Promise.resolve( lightNode );
            parser.cache.add( cacheKey, dependency );
            return dependency;

        }

        createNodeAttachment( nodeIndex ) {

            const self = this;
            const parser = this.parser;
            const json = parser.json;
            const nodeDef = json.nodes[ nodeIndex ];
            const lightDef = nodeDef.extensions && nodeDef.extensions[ this.name ] || {};
            const lightIndex = lightDef.light;
            if ( lightIndex === undefined ) return null;
            return this._loadLight( lightIndex ).then( function ( light ) {

                return parser._getNodeRef( self.cache, lightIndex, light );

            } );

        }

    }
    /**
     * Unlit Materials Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit
     */


    class GLTFMaterialsUnlitExtension {

        constructor() {

            this.name = EXTENSIONS.KHR_MATERIALS_UNLIT;

        }

        getMaterialType() {

            return THREE.MeshBasicMaterial;

        }

        extendParams( materialParams, materialDef, parser ) {

            const pending = [];
            materialParams.color = new THREE.Color( 1.0, 1.0, 1.0 );
            materialParams.opacity = 1.0;
            const metallicRoughness = materialDef.pbrMetallicRoughness;

            if ( metallicRoughness ) {

                if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

                    const array = metallicRoughness.baseColorFactor;
                    materialParams.color.fromArray( array );
                    materialParams.opacity = array[ 3 ];

                }

                if ( metallicRoughness.baseColorTexture !== undefined ) {

                    pending.push( parser.assignTexture( materialParams, 'map', metallicRoughness.baseColorTexture, THREE.sRGBEncoding ) );

                }

            }

            return Promise.all( pending );

        }

    }
    /**
     * Materials Emissive Strength Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/blob/5768b3ce0ef32bc39cdf1bef10b948586635ead3/extensions/2.0/Khronos/KHR_materials_emissive_strength/README.md
     */


    class GLTFMaterialsEmissiveStrengthExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_EMISSIVE_STRENGTH;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const emissiveStrength = materialDef.extensions[ this.name ].emissiveStrength;

            if ( emissiveStrength !== undefined ) {

                materialParams.emissiveIntensity = emissiveStrength;

            }

            return Promise.resolve();

        }

    }
    /**
     * Clearcoat Materials Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_clearcoat
     */


    class GLTFMaterialsClearcoatExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_CLEARCOAT;

        }

        getMaterialType( materialIndex ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];
            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;
            return THREE.MeshPhysicalMaterial;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const pending = [];
            const extension = materialDef.extensions[ this.name ];

            if ( extension.clearcoatFactor !== undefined ) {

                materialParams.clearcoat = extension.clearcoatFactor;

            }

            if ( extension.clearcoatTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'clearcoatMap', extension.clearcoatTexture ) );

            }

            if ( extension.clearcoatRoughnessFactor !== undefined ) {

                materialParams.clearcoatRoughness = extension.clearcoatRoughnessFactor;

            }

            if ( extension.clearcoatRoughnessTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'clearcoatRoughnessMap', extension.clearcoatRoughnessTexture ) );

            }

            if ( extension.clearcoatNormalTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'clearcoatNormalMap', extension.clearcoatNormalTexture ) );

                if ( extension.clearcoatNormalTexture.scale !== undefined ) {

                    const scale = extension.clearcoatNormalTexture.scale;
                    materialParams.clearcoatNormalScale = new THREE.Vector2( scale, scale );

                }

            }

            return Promise.all( pending );

        }

    }
    /**
     * Iridescence Materials Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_iridescence
     */


    class GLTFMaterialsIridescenceExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_IRIDESCENCE;

        }

        getMaterialType( materialIndex ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];
            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;
            return THREE.MeshPhysicalMaterial;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const pending = [];
            const extension = materialDef.extensions[ this.name ];

            if ( extension.iridescenceFactor !== undefined ) {

                materialParams.iridescence = extension.iridescenceFactor;

            }

            if ( extension.iridescenceTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'iridescenceMap', extension.iridescenceTexture ) );

            }

            if ( extension.iridescenceIor !== undefined ) {

                materialParams.iridescenceIOR = extension.iridescenceIor;

            }

            if ( materialParams.iridescenceThicknessRange === undefined ) {

                materialParams.iridescenceThicknessRange = [ 100, 400 ];

            }

            if ( extension.iridescenceThicknessMinimum !== undefined ) {

                materialParams.iridescenceThicknessRange[ 0 ] = extension.iridescenceThicknessMinimum;

            }

            if ( extension.iridescenceThicknessMaximum !== undefined ) {

                materialParams.iridescenceThicknessRange[ 1 ] = extension.iridescenceThicknessMaximum;

            }

            if ( extension.iridescenceThicknessTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'iridescenceThicknessMap', extension.iridescenceThicknessTexture ) );

            }

            return Promise.all( pending );

        }

    }
    /**
     * Sheen Materials Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_sheen
     */


    class GLTFMaterialsSheenExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_SHEEN;

        }

        getMaterialType( materialIndex ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];
            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;
            return THREE.MeshPhysicalMaterial;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const pending = [];
            materialParams.sheenColor = new THREE.Color( 0, 0, 0 );
            materialParams.sheenRoughness = 0;
            materialParams.sheen = 1;
            const extension = materialDef.extensions[ this.name ];

            if ( extension.sheenColorFactor !== undefined ) {

                materialParams.sheenColor.fromArray( extension.sheenColorFactor );

            }

            if ( extension.sheenRoughnessFactor !== undefined ) {

                materialParams.sheenRoughness = extension.sheenRoughnessFactor;

            }

            if ( extension.sheenColorTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'sheenColorMap', extension.sheenColorTexture, THREE.sRGBEncoding ) );

            }

            if ( extension.sheenRoughnessTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'sheenRoughnessMap', extension.sheenRoughnessTexture ) );

            }

            return Promise.all( pending );

        }

    }
    /**
     * Transmission Materials Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_transmission
     * Draft: https://github.com/KhronosGroup/glTF/pull/1698
     */


    class GLTFMaterialsTransmissionExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_TRANSMISSION;

        }

        getMaterialType( materialIndex ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];
            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;
            return THREE.MeshPhysicalMaterial;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const pending = [];
            const extension = materialDef.extensions[ this.name ];

            if ( extension.transmissionFactor !== undefined ) {

                materialParams.transmission = extension.transmissionFactor;

            }

            if ( extension.transmissionTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'transmissionMap', extension.transmissionTexture ) );

            }

            return Promise.all( pending );

        }

    }
    /**
     * Materials Volume Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_volume
     */


    class GLTFMaterialsVolumeExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_VOLUME;

        }

        getMaterialType( materialIndex ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];
            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;
            return THREE.MeshPhysicalMaterial;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const pending = [];
            const extension = materialDef.extensions[ this.name ];
            materialParams.thickness = extension.thicknessFactor !== undefined ? extension.thicknessFactor : 0;

            if ( extension.thicknessTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'thicknessMap', extension.thicknessTexture ) );

            }

            materialParams.attenuationDistance = extension.attenuationDistance || 0;
            const colorArray = extension.attenuationColor || [ 1, 1, 1 ];
            materialParams.attenuationColor = new THREE.Color( colorArray[ 0 ], colorArray[ 1 ], colorArray[ 2 ] );
            return Promise.all( pending );

        }

    }
    /**
     * Materials ior Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_ior
     */


    class GLTFMaterialsIorExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_IOR;

        }

        getMaterialType( materialIndex ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];
            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;
            return THREE.MeshPhysicalMaterial;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const extension = materialDef.extensions[ this.name ];
            materialParams.ior = extension.ior !== undefined ? extension.ior : 1.5;
            return Promise.resolve();

        }

    }
    /**
     * Materials specular Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_specular
     */


    class GLTFMaterialsSpecularExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_MATERIALS_SPECULAR;

        }

        getMaterialType( materialIndex ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];
            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) return null;
            return THREE.MeshPhysicalMaterial;

        }

        extendMaterialParams( materialIndex, materialParams ) {

            const parser = this.parser;
            const materialDef = parser.json.materials[ materialIndex ];

            if ( ! materialDef.extensions || ! materialDef.extensions[ this.name ] ) {

                return Promise.resolve();

            }

            const pending = [];
            const extension = materialDef.extensions[ this.name ];
            materialParams.specularIntensity = extension.specularFactor !== undefined ? extension.specularFactor : 1.0;

            if ( extension.specularTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'specularIntensityMap', extension.specularTexture ) );

            }

            const colorArray = extension.specularColorFactor || [ 1, 1, 1 ];
            materialParams.specularColor = new THREE.Color( colorArray[ 0 ], colorArray[ 1 ], colorArray[ 2 ] );

            if ( extension.specularColorTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'specularColorMap', extension.specularColorTexture, THREE.sRGBEncoding ) );

            }

            return Promise.all( pending );

        }

    }
    /**
     * BasisU THREE.Texture Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_basisu
     */


    class GLTFTextureBasisUExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.KHR_TEXTURE_BASISU;

        }

        loadTexture( textureIndex ) {

            const parser = this.parser;
            const json = parser.json;
            const textureDef = json.textures[ textureIndex ];

            if ( ! textureDef.extensions || ! textureDef.extensions[ this.name ] ) {

                return null;

            }

            const extension = textureDef.extensions[ this.name ];
            const loader = parser.options.ktx2Loader;

            if ( ! loader ) {

                if ( json.extensionsRequired && json.extensionsRequired.indexOf( this.name ) >= 0 ) {

                    throw new Error( 'THREE.GLTFLoader: setKTX2Loader must be called before loading KTX2 textures' );

                } else {

                    // Assumes that the extension is optional and that a fallback texture is present
                    return null;

                }

            }

            return parser.loadTextureImage( textureIndex, extension.source, loader );

        }

    }
    /**
     * WebP THREE.Texture Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_texture_webp
     */


    class GLTFTextureWebPExtension {

        constructor( parser ) {

            this.parser = parser;
            this.name = EXTENSIONS.EXT_TEXTURE_WEBP;
            this.isSupported = null;

        }

        loadTexture( textureIndex ) {

            const name = this.name;
            const parser = this.parser;
            const json = parser.json;
            const textureDef = json.textures[ textureIndex ];

            if ( ! textureDef.extensions || ! textureDef.extensions[ name ] ) {

                return null;

            }

            const extension = textureDef.extensions[ name ];
            const source = json.images[ extension.source ];
            let loader = parser.textureLoader;

            if ( source.uri ) {

                const handler = parser.options.manager.getHandler( source.uri );
                if ( handler !== null ) loader = handler;

            }

            return this.detectSupport().then( function ( isSupported ) {

                if ( isSupported ) return parser.loadTextureImage( textureIndex, extension.source, loader );

                if ( json.extensionsRequired && json.extensionsRequired.indexOf( name ) >= 0 ) {

                    throw new Error( 'THREE.GLTFLoader: WebP required by asset but unsupported.' );

                } // Fall back to PNG or JPEG.


                return parser.loadTexture( textureIndex );

            } );

        }

        detectSupport() {

            if ( ! this.isSupported ) {

                this.isSupported = new Promise( function ( resolve ) {

                    const image = new Image(); // Lossy test image. Support for lossy images doesn't guarantee support for all
                    // WebP images, unfortunately.

                    image.src = 'data:image/webp;base64,UklGRiIAAABXRUJQVlA4IBYAAAAwAQCdASoBAAEADsD+JaQAA3AAAAAA';

                    image.onload = image.onerror = function () {

                        resolve( image.height === 1 );

                    };

                } );

            }

            return this.isSupported;

        }

    }
    /**
     * meshopt BufferView Compression Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_meshopt_compression
     */


    class GLTFMeshoptCompression {

        constructor( parser ) {

            this.name = EXTENSIONS.EXT_MESHOPT_COMPRESSION;
            this.parser = parser;

        }

        loadBufferView( index ) {

            const json = this.parser.json;
            const bufferView = json.bufferViews[ index ];

            if ( bufferView.extensions && bufferView.extensions[ this.name ] ) {

                const extensionDef = bufferView.extensions[ this.name ];
                const buffer = this.parser.getDependency( 'buffer', extensionDef.buffer );
                const decoder = this.parser.options.meshoptDecoder;

                if ( ! decoder || ! decoder.supported ) {

                    if ( json.extensionsRequired && json.extensionsRequired.indexOf( this.name ) >= 0 ) {

                        throw new Error( 'THREE.GLTFLoader: setMeshoptDecoder must be called before loading compressed files' );

                    } else {

                        // Assumes that the extension is optional and that fallback buffer data is present
                        return null;

                    }

                }

                return Promise.all( [ buffer, decoder.ready ] ).then( function ( res ) {

                    const byteOffset = extensionDef.byteOffset || 0;
                    const byteLength = extensionDef.byteLength || 0;
                    const count = extensionDef.count;
                    const stride = extensionDef.byteStride;
                    const result = new ArrayBuffer( count * stride );
                    const source = new Uint8Array( res[ 0 ], byteOffset, byteLength );
                    decoder.decodeGltfBuffer( new Uint8Array( result ), count, stride, source, extensionDef.mode, extensionDef.filter );
                    return result;

                } );

            } else {

                return null;

            }

        }

    }
    /* BINARY EXTENSION */


    const BINARY_EXTENSION_HEADER_MAGIC = 'glTF';
    const BINARY_EXTENSION_HEADER_LENGTH = 12;
    const BINARY_EXTENSION_CHUNK_TYPES = {
        JSON: 0x4E4F534A,
        BIN: 0x004E4942
    };

    class GLTFBinaryExtension {

        constructor( data ) {

            this.name = EXTENSIONS.KHR_BINARY_GLTF;
            this.content = null;
            this.body = null;
            const headerView = new DataView( data, 0, BINARY_EXTENSION_HEADER_LENGTH );
            this.header = {
                magic: THREE.LoaderUtils.decodeText( new Uint8Array( data.slice( 0, 4 ) ) ),
                version: headerView.getUint32( 4, true ),
                length: headerView.getUint32( 8, true )
            };

            if ( this.header.magic !== BINARY_EXTENSION_HEADER_MAGIC ) {

                throw new Error( 'THREE.GLTFLoader: Unsupported glTF-Binary header.' );

            } else if ( this.header.version < 2.0 ) {

                throw new Error( 'THREE.GLTFLoader: Legacy binary file detected.' );

            }

            const chunkContentsLength = this.header.length - BINARY_EXTENSION_HEADER_LENGTH;
            const chunkView = new DataView( data, BINARY_EXTENSION_HEADER_LENGTH );
            let chunkIndex = 0;

            while ( chunkIndex < chunkContentsLength ) {

                const chunkLength = chunkView.getUint32( chunkIndex, true );
                chunkIndex += 4;
                const chunkType = chunkView.getUint32( chunkIndex, true );
                chunkIndex += 4;

                if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.JSON ) {

                    const contentArray = new Uint8Array( data, BINARY_EXTENSION_HEADER_LENGTH + chunkIndex, chunkLength );
                    this.content = THREE.LoaderUtils.decodeText( contentArray );

                } else if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.BIN ) {

                    const byteOffset = BINARY_EXTENSION_HEADER_LENGTH + chunkIndex;
                    this.body = data.slice( byteOffset, byteOffset + chunkLength );

                } // Clients must ignore chunks with unknown types.


                chunkIndex += chunkLength;

            }

            if ( this.content === null ) {

                throw new Error( 'THREE.GLTFLoader: JSON content not found.' );

            }

        }

    }
    /**
     * DRACO THREE.Mesh Compression Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_draco_mesh_compression
     */


    class GLTFDracoMeshCompressionExtension {

        constructor( json, dracoLoader ) {

            if ( ! dracoLoader ) {

                throw new Error( 'THREE.GLTFLoader: No DRACOLoader instance provided.' );

            }

            this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION;
            this.json = json;
            this.dracoLoader = dracoLoader;
            this.dracoLoader.preload();

        }

        decodePrimitive( primitive, parser ) {

            const json = this.json;
            const dracoLoader = this.dracoLoader;
            const bufferViewIndex = primitive.extensions[ this.name ].bufferView;
            const gltfAttributeMap = primitive.extensions[ this.name ].attributes;
            const threeAttributeMap = {};
            const attributeNormalizedMap = {};
            const attributeTypeMap = {};

            for ( const attributeName in gltfAttributeMap ) {

                const threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();
                threeAttributeMap[ threeAttributeName ] = gltfAttributeMap[ attributeName ];

            }

            for ( const attributeName in primitive.attributes ) {

                const threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();

                if ( gltfAttributeMap[ attributeName ] !== undefined ) {

                    const accessorDef = json.accessors[ primitive.attributes[ attributeName ] ];
                    const componentType = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ];
                    attributeTypeMap[ threeAttributeName ] = componentType;
                    attributeNormalizedMap[ threeAttributeName ] = accessorDef.normalized === true;

                }

            }

            return parser.getDependency( 'bufferView', bufferViewIndex ).then( function ( bufferView ) {

                return new Promise( function ( resolve ) {

                    dracoLoader.decodeDracoFile( bufferView, function ( geometry ) {

                        for ( const attributeName in geometry.attributes ) {

                            const attribute = geometry.attributes[ attributeName ];
                            const normalized = attributeNormalizedMap[ attributeName ];
                            if ( normalized !== undefined ) attribute.normalized = normalized;

                        }

                        resolve( geometry );

                    }, threeAttributeMap, attributeTypeMap );

                } );

            } );

        }

    }
    /**
     * THREE.Texture Transform Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_transform
     */


    class GLTFTextureTransformExtension {

        constructor() {

            this.name = EXTENSIONS.KHR_TEXTURE_TRANSFORM;

        }

        extendTexture( texture, transform ) {

            if ( transform.texCoord !== undefined ) {

                console.warn( 'THREE.GLTFLoader: Custom UV sets in "' + this.name + '" extension not yet supported.' );

            }

            if ( transform.offset === undefined && transform.rotation === undefined && transform.scale === undefined ) {

                // See https://github.com/mrdoob/three.js/issues/21819.
                return texture;

            }

            texture = texture.clone();

            if ( transform.offset !== undefined ) {

                texture.offset.fromArray( transform.offset );

            }

            if ( transform.rotation !== undefined ) {

                texture.rotation = transform.rotation;

            }

            if ( transform.scale !== undefined ) {

                texture.repeat.fromArray( transform.scale );

            }

            texture.needsUpdate = true;
            return texture;

        }

    }
    /**
     * Specular-Glossiness Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Archived/KHR_materials_pbrSpecularGlossiness
     */

    /**
     * A sub class of StandardMaterial with some of the functionality
     * changed via the `onBeforeCompile` callback
     * @pailhead
     */


    class GLTFMeshStandardSGMaterial extends THREE.MeshStandardMaterial {

        constructor( params ) {

            super();
            this.isGLTFSpecularGlossinessMaterial = true; //various chunks that need replacing

            const specularMapParsFragmentChunk = [ '#ifdef USE_SPECULARMAP', '	uniform sampler2D specularMap;', '#endif' ].join( '\n' );
            const glossinessMapParsFragmentChunk = [ '#ifdef USE_GLOSSINESSMAP', '	uniform sampler2D glossinessMap;', '#endif' ].join( '\n' );
            const specularMapFragmentChunk = [ 'vec3 specularFactor = specular;', '#ifdef USE_SPECULARMAP', '	vec4 texelSpecular = texture2D( specularMap, vUv );', '	// reads channel RGB, compatible with a glTF Specular-Glossiness (RGBA) texture', '	specularFactor *= texelSpecular.rgb;', '#endif' ].join( '\n' );
            const glossinessMapFragmentChunk = [ 'float glossinessFactor = glossiness;', '#ifdef USE_GLOSSINESSMAP', '	vec4 texelGlossiness = texture2D( glossinessMap, vUv );', '	// reads channel A, compatible with a glTF Specular-Glossiness (RGBA) texture', '	glossinessFactor *= texelGlossiness.a;', '#endif' ].join( '\n' );
            const lightPhysicalFragmentChunk = [ 'PhysicalMaterial material;', 'material.diffuseColor = diffuseColor.rgb * ( 1. - max( specularFactor.r, max( specularFactor.g, specularFactor.b ) ) );', 'vec3 dxy = max( abs( dFdx( geometryNormal ) ), abs( dFdy( geometryNormal ) ) );', 'float geometryRoughness = max( max( dxy.x, dxy.y ), dxy.z );', 'material.roughness = max( 1.0 - glossinessFactor, 0.0525 ); // 0.0525 corresponds to the base mip of a 256 cubemap.', 'material.roughness += geometryRoughness;', 'material.roughness = min( material.roughness, 1.0 );', 'material.specularColor = specularFactor;' ].join( '\n' );
            const uniforms = {
                specular: {
                    value: new THREE.Color().setHex( 0xffffff )
                },
                glossiness: {
                    value: 1
                },
                specularMap: {
                    value: null
                },
                glossinessMap: {
                    value: null
                }
            };
            this._extraUniforms = uniforms;

            this.onBeforeCompile = function ( shader ) {

                for ( const uniformName in uniforms ) {

                    shader.uniforms[ uniformName ] = uniforms[ uniformName ];

                }

                shader.fragmentShader = shader.fragmentShader.replace( 'uniform float roughness;', 'uniform vec3 specular;' ).replace( 'uniform float metalness;', 'uniform float glossiness;' ).replace( '#include <roughnessmap_pars_fragment>', specularMapParsFragmentChunk ).replace( '#include <metalnessmap_pars_fragment>', glossinessMapParsFragmentChunk ).replace( '#include <roughnessmap_fragment>', specularMapFragmentChunk ).replace( '#include <metalnessmap_fragment>', glossinessMapFragmentChunk ).replace( '#include <lights_physical_fragment>', lightPhysicalFragmentChunk );

            };

            Object.defineProperties( this, {
                specular: {
                    get: function () {

                        return uniforms.specular.value;

                    },
                    set: function ( v ) {

                        uniforms.specular.value = v;

                    }
                },
                specularMap: {
                    get: function () {

                        return uniforms.specularMap.value;

                    },
                    set: function ( v ) {

                        uniforms.specularMap.value = v;

                        if ( v ) {

                            this.defines.USE_SPECULARMAP = ''; // USE_UV is set by the renderer for specular maps

                        } else {

                            delete this.defines.USE_SPECULARMAP;

                        }

                    }
                },
                glossiness: {
                    get: function () {

                        return uniforms.glossiness.value;

                    },
                    set: function ( v ) {

                        uniforms.glossiness.value = v;

                    }
                },
                glossinessMap: {
                    get: function () {

                        return uniforms.glossinessMap.value;

                    },
                    set: function ( v ) {

                        uniforms.glossinessMap.value = v;

                        if ( v ) {

                            this.defines.USE_GLOSSINESSMAP = '';
                            this.defines.USE_UV = '';

                        } else {

                            delete this.defines.USE_GLOSSINESSMAP;
                            delete this.defines.USE_UV;

                        }

                    }
                }
            } );
            delete this.metalness;
            delete this.roughness;
            delete this.metalnessMap;
            delete this.roughnessMap;
            this.setValues( params );

        }

        copy( source ) {

            super.copy( source );
            this.specularMap = source.specularMap;
            this.specular.copy( source.specular );
            this.glossinessMap = source.glossinessMap;
            this.glossiness = source.glossiness;
            delete this.metalness;
            delete this.roughness;
            delete this.metalnessMap;
            delete this.roughnessMap;
            return this;

        }

    }

    class GLTFMaterialsPbrSpecularGlossinessExtension {

        constructor() {

            this.name = EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS;
            this.specularGlossinessParams = [ 'color', 'map', 'lightMap', 'lightMapIntensity', 'aoMap', 'aoMapIntensity', 'emissive', 'emissiveIntensity', 'emissiveMap', 'bumpMap', 'bumpScale', 'normalMap', 'normalMapType', 'displacementMap', 'displacementScale', 'displacementBias', 'specularMap', 'specular', 'glossinessMap', 'glossiness', 'alphaMap', 'envMap', 'envMapIntensity' ];

        }

        getMaterialType() {

            return GLTFMeshStandardSGMaterial;

        }

        extendParams( materialParams, materialDef, parser ) {

            const pbrSpecularGlossiness = materialDef.extensions[ this.name ];
            materialParams.color = new THREE.Color( 1.0, 1.0, 1.0 );
            materialParams.opacity = 1.0;
            const pending = [];

            if ( Array.isArray( pbrSpecularGlossiness.diffuseFactor ) ) {

                const array = pbrSpecularGlossiness.diffuseFactor;
                materialParams.color.fromArray( array );
                materialParams.opacity = array[ 3 ];

            }

            if ( pbrSpecularGlossiness.diffuseTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'map', pbrSpecularGlossiness.diffuseTexture, THREE.sRGBEncoding ) );

            }

            materialParams.emissive = new THREE.Color( 0.0, 0.0, 0.0 );
            materialParams.glossiness = pbrSpecularGlossiness.glossinessFactor !== undefined ? pbrSpecularGlossiness.glossinessFactor : 1.0;
            materialParams.specular = new THREE.Color( 1.0, 1.0, 1.0 );

            if ( Array.isArray( pbrSpecularGlossiness.specularFactor ) ) {

                materialParams.specular.fromArray( pbrSpecularGlossiness.specularFactor );

            }

            if ( pbrSpecularGlossiness.specularGlossinessTexture !== undefined ) {

                const specGlossMapDef = pbrSpecularGlossiness.specularGlossinessTexture;
                pending.push( parser.assignTexture( materialParams, 'glossinessMap', specGlossMapDef ) );
                pending.push( parser.assignTexture( materialParams, 'specularMap', specGlossMapDef, THREE.sRGBEncoding ) );

            }

            return Promise.all( pending );

        }

        createMaterial( materialParams ) {

            const material = new GLTFMeshStandardSGMaterial( materialParams );
            material.fog = true;
            material.color = materialParams.color;
            material.map = materialParams.map === undefined ? null : materialParams.map;
            material.lightMap = null;
            material.lightMapIntensity = 1.0;
            material.aoMap = materialParams.aoMap === undefined ? null : materialParams.aoMap;
            material.aoMapIntensity = 1.0;
            material.emissive = materialParams.emissive;
            material.emissiveIntensity = materialParams.emissiveIntensity === undefined ? 1.0 : materialParams.emissiveIntensity;
            material.emissiveMap = materialParams.emissiveMap === undefined ? null : materialParams.emissiveMap;
            material.bumpMap = materialParams.bumpMap === undefined ? null : materialParams.bumpMap;
            material.bumpScale = 1;
            material.normalMap = materialParams.normalMap === undefined ? null : materialParams.normalMap;
            material.normalMapType = THREE.TangentSpaceNormalMap;
            if ( materialParams.normalScale ) material.normalScale = materialParams.normalScale;
            material.displacementMap = null;
            material.displacementScale = 1;
            material.displacementBias = 0;
            material.specularMap = materialParams.specularMap === undefined ? null : materialParams.specularMap;
            material.specular = materialParams.specular;
            material.glossinessMap = materialParams.glossinessMap === undefined ? null : materialParams.glossinessMap;
            material.glossiness = materialParams.glossiness;
            material.alphaMap = null;
            material.envMap = materialParams.envMap === undefined ? null : materialParams.envMap;
            material.envMapIntensity = 1.0;
            return material;

        }

    }
    /**
     * THREE.Mesh Quantization Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_mesh_quantization
     */


    class GLTFMeshQuantizationExtension {

        constructor() {

            this.name = EXTENSIONS.KHR_MESH_QUANTIZATION;

        }

    }
    /*********************************/

    /********** INTERPOLATION ********/

    /*********************************/
    // Spline Interpolation
    // Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#appendix-c-spline-interpolation


    class GLTFCubicSplineInterpolant extends THREE.Interpolant {

        constructor( parameterPositions, sampleValues, sampleSize, resultBuffer ) {

            super( parameterPositions, sampleValues, sampleSize, resultBuffer );

        }

        copySampleValue_( index ) {

            // Copies a sample value to the result buffer. See description of glTF
            // CUBICSPLINE values layout in interpolate_() function below.
            const result = this.resultBuffer,
                values = this.sampleValues,
                valueSize = this.valueSize,
                offset = index * valueSize * 3 + valueSize;

            for ( let i = 0; i !== valueSize; i ++ ) {

                result[ i ] = values[ offset + i ];

            }

            return result;

        }

        interpolate_( i1, t0, t, t1 ) {

            const result = this.resultBuffer;
            const values = this.sampleValues;
            const stride = this.valueSize;
            const stride2 = stride * 2;
            const stride3 = stride * 3;
            const td = t1 - t0;
            const p = ( t - t0 ) / td;
            const pp = p * p;
            const ppp = pp * p;
            const offset1 = i1 * stride3;
            const offset0 = offset1 - stride3;
            const s2 = - 2 * ppp + 3 * pp;
            const s3 = ppp - pp;
            const s0 = 1 - s2;
            const s1 = s3 - pp + p; // Layout of keyframe output values for CUBICSPLINE animations:
            //   [ inTangent_1, splineVertex_1, outTangent_1, inTangent_2, splineVertex_2, ... ]

            for ( let i = 0; i !== stride; i ++ ) {

                const p0 = values[ offset0 + i + stride ]; // splineVertex_k

                const m0 = values[ offset0 + i + stride2 ] * td; // outTangent_k * (t_k+1 - t_k)

                const p1 = values[ offset1 + i + stride ]; // splineVertex_k+1

                const m1 = values[ offset1 + i ] * td; // inTangent_k+1 * (t_k+1 - t_k)

                result[ i ] = s0 * p0 + s1 * m0 + s2 * p1 + s3 * m1;

            }

            return result;

        }

    }

    const _q = new THREE.Quaternion();

    class GLTFCubicSplineQuaternionInterpolant extends GLTFCubicSplineInterpolant {

        interpolate_( i1, t0, t, t1 ) {

            const result = super.interpolate_( i1, t0, t, t1 );

            _q.fromArray( result ).normalize().toArray( result );

            return result;

        }

    }
    /*********************************/

    /********** INTERNALS ************/

    /*********************************/

    /* CONSTANTS */


    const WEBGL_CONSTANTS = {
        FLOAT: 5126,
        //FLOAT_MAT2: 35674,
        FLOAT_MAT3: 35675,
        FLOAT_MAT4: 35676,
        FLOAT_VEC2: 35664,
        FLOAT_VEC3: 35665,
        FLOAT_VEC4: 35666,
        LINEAR: 9729,
        REPEAT: 10497,
        SAMPLER_2D: 35678,
        POINTS: 0,
        LINES: 1,
        LINE_LOOP: 2,
        LINE_STRIP: 3,
        TRIANGLES: 4,
        TRIANGLE_STRIP: 5,
        TRIANGLE_FAN: 6,
        UNSIGNED_BYTE: 5121,
        UNSIGNED_SHORT: 5123
    };
    const WEBGL_COMPONENT_TYPES = {
        5120: Int8Array,
        5121: Uint8Array,
        5122: Int16Array,
        5123: Uint16Array,
        5125: Uint32Array,
        5126: Float32Array
    };
    const WEBGL_FILTERS = {
        9728: THREE.NearestFilter,
        9729: THREE.LinearFilter,
        9984: THREE.NearestMipmapNearestFilter,
        9985: THREE.LinearMipmapNearestFilter,
        9986: THREE.NearestMipmapLinearFilter,
        9987: THREE.LinearMipmapLinearFilter
    };
    const WEBGL_WRAPPINGS = {
        33071: THREE.ClampToEdgeWrapping,
        33648: THREE.MirroredRepeatWrapping,
        10497: THREE.RepeatWrapping
    };
    const WEBGL_TYPE_SIZES = {
        'SCALAR': 1,
        'VEC2': 2,
        'VEC3': 3,
        'VEC4': 4,
        'MAT2': 4,
        'MAT3': 9,
        'MAT4': 16
    };
    const ATTRIBUTES = {
        POSITION: 'position',
        NORMAL: 'normal',
        TANGENT: 'tangent',
        TEXCOORD_0: 'uv',
        TEXCOORD_1: 'uv2',
        COLOR_0: 'color',
        WEIGHTS_0: 'skinWeight',
        JOINTS_0: 'skinIndex'
    };
    const PATH_PROPERTIES = {
        scale: 'scale',
        translation: 'position',
        rotation: 'quaternion',
        weights: 'morphTargetInfluences'
    };
    const INTERPOLATION = {
        CUBICSPLINE: undefined,
        // We use a custom interpolant (GLTFCubicSplineInterpolation) for CUBICSPLINE tracks. Each
        // keyframe track will be initialized with a default interpolation type, then modified.
        LINEAR: THREE.InterpolateLinear,
        STEP: THREE.InterpolateDiscrete
    };
    const ALPHA_MODES = {
        OPAQUE: 'OPAQUE',
        MASK: 'MASK',
        BLEND: 'BLEND'
    };
    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#default-material
     */

    function createDefaultMaterial( cache ) {

        if ( cache[ 'DefaultMaterial' ] === undefined ) {

            cache[ 'DefaultMaterial' ] = new THREE.MeshStandardMaterial( {
                color: 0xFFFFFF,
                emissive: 0x000000,
                metalness: 1,
                roughness: 1,
                transparent: false,
                depthTest: true,
                side: THREE.FrontSide
            } );

        }

        return cache[ 'DefaultMaterial' ];

    }

    function addUnknownExtensionsToUserData( knownExtensions, object, objectDef ) {

        // Add unknown glTF extensions to an object's userData.
        for ( const name in objectDef.extensions ) {

            if ( knownExtensions[ name ] === undefined ) {

                object.userData.gltfExtensions = object.userData.gltfExtensions || {};
                object.userData.gltfExtensions[ name ] = objectDef.extensions[ name ];

            }

        }

    }
    /**
     * @param {Object3D|Material|BufferGeometry} object
     * @param {GLTF.definition} gltfDef
     */


    function assignExtrasToUserData( object, gltfDef ) {

        if ( gltfDef.extras !== undefined ) {

            if ( typeof gltfDef.extras === 'object' ) {

                Object.assign( object.userData, gltfDef.extras );

            } else {

                console.warn( 'THREE.GLTFLoader: Ignoring primitive type .extras, ' + gltfDef.extras );

            }

        }

    }
    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#morph-targets
     *
     * @param {BufferGeometry} geometry
     * @param {Array<GLTF.Target>} targets
     * @param {GLTFParser} parser
     * @return {Promise<BufferGeometry>}
     */


    function addMorphTargets( geometry, targets, parser ) {

        let hasMorphPosition = false;
        let hasMorphNormal = false;
        let hasMorphColor = false;

        for ( let i = 0, il = targets.length; i < il; i ++ ) {

            const target = targets[ i ];
            if ( target.POSITION !== undefined ) hasMorphPosition = true;
            if ( target.NORMAL !== undefined ) hasMorphNormal = true;
            if ( target.COLOR_0 !== undefined ) hasMorphColor = true;
            if ( hasMorphPosition && hasMorphNormal && hasMorphColor ) break;

        }

        if ( ! hasMorphPosition && ! hasMorphNormal && ! hasMorphColor ) return Promise.resolve( geometry );
        const pendingPositionAccessors = [];
        const pendingNormalAccessors = [];
        const pendingColorAccessors = [];

        for ( let i = 0, il = targets.length; i < il; i ++ ) {

            const target = targets[ i ];

            if ( hasMorphPosition ) {

                const pendingAccessor = target.POSITION !== undefined ? parser.getDependency( 'accessor', target.POSITION ) : geometry.attributes.position;
                pendingPositionAccessors.push( pendingAccessor );

            }

            if ( hasMorphNormal ) {

                const pendingAccessor = target.NORMAL !== undefined ? parser.getDependency( 'accessor', target.NORMAL ) : geometry.attributes.normal;
                pendingNormalAccessors.push( pendingAccessor );

            }

            if ( hasMorphColor ) {

                const pendingAccessor = target.COLOR_0 !== undefined ? parser.getDependency( 'accessor', target.COLOR_0 ) : geometry.attributes.color;
                pendingColorAccessors.push( pendingAccessor );

            }

        }

        return Promise.all( [ Promise.all( pendingPositionAccessors ), Promise.all( pendingNormalAccessors ), Promise.all( pendingColorAccessors ) ] ).then( function ( accessors ) {

            const morphPositions = accessors[ 0 ];
            const morphNormals = accessors[ 1 ];
            const morphColors = accessors[ 2 ];
            if ( hasMorphPosition ) geometry.morphAttributes.position = morphPositions;
            if ( hasMorphNormal ) geometry.morphAttributes.normal = morphNormals;
            if ( hasMorphColor ) geometry.morphAttributes.color = morphColors;
            geometry.morphTargetsRelative = true;
            return geometry;

        } );

    }
    /**
     * @param {Mesh} mesh
     * @param {GLTF.Mesh} meshDef
     */


    function updateMorphTargets( mesh, meshDef ) {

        mesh.updateMorphTargets();

        if ( meshDef.weights !== undefined ) {

            for ( let i = 0, il = meshDef.weights.length; i < il; i ++ ) {

                mesh.morphTargetInfluences[ i ] = meshDef.weights[ i ];

            }

        } // .extras has user-defined data, so check that .extras.targetNames is an array.


        if ( meshDef.extras && Array.isArray( meshDef.extras.targetNames ) ) {

            const targetNames = meshDef.extras.targetNames;

            if ( mesh.morphTargetInfluences.length === targetNames.length ) {

                mesh.morphTargetDictionary = {};

                for ( let i = 0, il = targetNames.length; i < il; i ++ ) {

                    mesh.morphTargetDictionary[ targetNames[ i ] ] = i;

                }

            } else {

                console.warn( 'THREE.GLTFLoader: Invalid extras.targetNames length. Ignoring names.' );

            }

        }

    }

    function createPrimitiveKey( primitiveDef ) {

        const dracoExtension = primitiveDef.extensions && primitiveDef.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ];
        let geometryKey;

        if ( dracoExtension ) {

            geometryKey = 'draco:' + dracoExtension.bufferView + ':' + dracoExtension.indices + ':' + createAttributesKey( dracoExtension.attributes );

        } else {

            geometryKey = primitiveDef.indices + ':' + createAttributesKey( primitiveDef.attributes ) + ':' + primitiveDef.mode;

        }

        return geometryKey;

    }

    function createAttributesKey( attributes ) {

        let attributesKey = '';
        const keys = Object.keys( attributes ).sort();

        for ( let i = 0, il = keys.length; i < il; i ++ ) {

            attributesKey += keys[ i ] + ':' + attributes[ keys[ i ] ] + ';';

        }

        return attributesKey;

    }

    function getNormalizedComponentScale( constructor ) {

        // Reference:
        // https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_mesh_quantization#encoding-quantized-data
        switch ( constructor ) {

        case Int8Array:
            return 1 / 127;

        case Uint8Array:
            return 1 / 255;

        case Int16Array:
            return 1 / 32767;

        case Uint16Array:
            return 1 / 65535;

        default:
            throw new Error( 'THREE.GLTFLoader: Unsupported normalized accessor component type.' );

        }

    }

    function getImageURIMimeType( uri ) {

        if ( uri.search( /\.jpe?g($|\?)/i ) > 0 || uri.search( /^data\:image\/jpeg/ ) === 0 ) return 'image/jpeg';
        if ( uri.search( /\.webp($|\?)/i ) > 0 || uri.search( /^data\:image\/webp/ ) === 0 ) return 'image/webp';
        return 'image/png';

    }
    /* GLTF PARSER */


    class GLTFParser {

        constructor( json = {}, options = {} ) {

            this.json = json;
            this.extensions = {};
            this.plugins = {};
            this.options = options; // loader object cache

            this.cache = new GLTFRegistry(); // associations between Three.js objects and glTF elements

            this.associations = new Map(); // THREE.BufferGeometry caching

            this.primitiveCache = {}; // THREE.Object3D instance caches

            this.meshCache = {
                refs: {},
                uses: {}
            };
            this.cameraCache = {
                refs: {},
                uses: {}
            };
            this.lightCache = {
                refs: {},
                uses: {}
            };
            this.sourceCache = {};
            this.textureCache = {}; // Track node names, to ensure no duplicates

            this.nodeNamesUsed = {}; // Use an THREE.ImageBitmapLoader if imageBitmaps are supported. Moves much of the
            // expensive work of uploading a texture to the GPU off the main thread.

            const isSafari = /^((?!chrome|android).)*safari/i.test( navigator.userAgent ) === true;
            const isFirefox = navigator.userAgent.indexOf( 'Firefox' ) > - 1;
            const firefoxVersion = isFirefox ? navigator.userAgent.match( /Firefox\/([0-9]+)\./ )[ 1 ] : - 1;

            if ( typeof createImageBitmap === 'undefined' || isSafari || isFirefox && firefoxVersion < 98 ) {

                this.textureLoader = new THREE.TextureLoader( this.options.manager );

            } else {

                this.textureLoader = new THREE.ImageBitmapLoader( this.options.manager );

            }

            this.textureLoader.setCrossOrigin( this.options.crossOrigin );
            this.textureLoader.setRequestHeader( this.options.requestHeader );
            this.fileLoader = new THREE.FileLoader( this.options.manager );
            this.fileLoader.setResponseType( 'arraybuffer' );

            if ( this.options.crossOrigin === 'use-credentials' ) {

                this.fileLoader.setWithCredentials( true );

            }

        }

        setExtensions( extensions ) {

            this.extensions = extensions;

        }

        setPlugins( plugins ) {

            this.plugins = plugins;

        }

        parse( onLoad, onError ) {

            const parser = this;
            const json = this.json;
            const extensions = this.extensions; // Clear the loader cache

            this.cache.removeAll(); // Mark the special nodes/meshes in json for efficient parse

            this._invokeAll( function ( ext ) {

                return ext._markDefs && ext._markDefs();

            } );

            Promise.all( this._invokeAll( function ( ext ) {

                return ext.beforeRoot && ext.beforeRoot();

            } ) ).then( function () {

                return Promise.all( [ parser.getDependencies( 'scene' ), parser.getDependencies( 'animation' ), parser.getDependencies( 'camera' ) ] );

            } ).then( function ( dependencies ) {

                const result = {
                    scene: dependencies[ 0 ][ json.scene || 0 ],
                    scenes: dependencies[ 0 ],
                    animations: dependencies[ 1 ],
                    cameras: dependencies[ 2 ],
                    asset: json.asset,
                    parser: parser,
                    userData: {}
                };
                addUnknownExtensionsToUserData( extensions, result, json );
                assignExtrasToUserData( result, json );
                Promise.all( parser._invokeAll( function ( ext ) {

                    return ext.afterRoot && ext.afterRoot( result );

                } ) ).then( function () {

                    onLoad( result );

                } );

            } ).catch( onError );

        }
        /**
         * Marks the special nodes/meshes in json for efficient parse.
         */


        _markDefs() {

            const nodeDefs = this.json.nodes || [];
            const skinDefs = this.json.skins || [];
            const meshDefs = this.json.meshes || []; // Nothing in the node definition indicates whether it is a THREE.Bone or an
            // THREE.Object3D. Use the skins' joint references to mark bones.

            for ( let skinIndex = 0, skinLength = skinDefs.length; skinIndex < skinLength; skinIndex ++ ) {

                const joints = skinDefs[ skinIndex ].joints;

                for ( let i = 0, il = joints.length; i < il; i ++ ) {

                    nodeDefs[ joints[ i ] ].isBone = true;

                }

            } // Iterate over all nodes, marking references to shared resources,
            // as well as skeleton joints.


            for ( let nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex ++ ) {

                const nodeDef = nodeDefs[ nodeIndex ];

                if ( nodeDef.mesh !== undefined ) {

                    this._addNodeRef( this.meshCache, nodeDef.mesh ); // Nothing in the mesh definition indicates whether it is
                    // a THREE.SkinnedMesh or THREE.Mesh. Use the node's mesh reference
                    // to mark THREE.SkinnedMesh if node has skin.


                    if ( nodeDef.skin !== undefined ) {

                        meshDefs[ nodeDef.mesh ].isSkinnedMesh = true;

                    }

                }

                if ( nodeDef.camera !== undefined ) {

                    this._addNodeRef( this.cameraCache, nodeDef.camera );

                }

            }

        }
        /**
         * Counts references to shared node / THREE.Object3D resources. These resources
         * can be reused, or "instantiated", at multiple nodes in the scene
         * hierarchy. THREE.Mesh, Camera, and Light instances are instantiated and must
         * be marked. Non-scenegraph resources (like Materials, Geometries, and
         * Textures) can be reused directly and are not marked here.
         *
         * Example: CesiumMilkTruck sample model reuses "Wheel" meshes.
         */


        _addNodeRef( cache, index ) {

            if ( index === undefined ) return;

            if ( cache.refs[ index ] === undefined ) {

                cache.refs[ index ] = cache.uses[ index ] = 0;

            }

            cache.refs[ index ] ++;

        }
        /** Returns a reference to a shared resource, cloning it if necessary. */


        _getNodeRef( cache, index, object ) {

            if ( cache.refs[ index ] <= 1 ) return object;
            const ref = object.clone(); // Propagates mappings to the cloned object, prevents mappings on the
            // original object from being lost.

            const updateMappings = ( original, clone ) => {

                const mappings = this.associations.get( original );

                if ( mappings != null ) {

                    this.associations.set( clone, mappings );

                }

                for ( const [ i, child ] of original.children.entries() ) {

                    updateMappings( child, clone.children[ i ] );

                }

            };

            updateMappings( object, ref );
            ref.name += '_instance_' + cache.uses[ index ] ++;
            return ref;

        }

        _invokeOne( func ) {

            const extensions = Object.values( this.plugins );
            extensions.push( this );

            for ( let i = 0; i < extensions.length; i ++ ) {

                const result = func( extensions[ i ] );
                if ( result ) return result;

            }

            return null;

        }

        _invokeAll( func ) {

            const extensions = Object.values( this.plugins );
            extensions.unshift( this );
            const pending = [];

            for ( let i = 0; i < extensions.length; i ++ ) {

                const result = func( extensions[ i ] );
                if ( result ) pending.push( result );

            }

            return pending;

        }
        /**
         * Requests the specified dependency asynchronously, with caching.
         * @param {string} type
         * @param {number} index
         * @return {Promise<Object3D|Material|THREE.Texture|AnimationClip|ArrayBuffer|Object>}
         */


        getDependency( type, index ) {

            const cacheKey = type + ':' + index;
            let dependency = this.cache.get( cacheKey );

            if ( ! dependency ) {

                switch ( type ) {

                case 'scene':
                    dependency = this.loadScene( index );
                    break;

                case 'node':
                    dependency = this.loadNode( index );
                    break;

                case 'mesh':
                    dependency = this._invokeOne( function ( ext ) {

                        return ext.loadMesh && ext.loadMesh( index );

                    } );
                    break;

                case 'accessor':
                    dependency = this.loadAccessor( index );
                    break;

                case 'bufferView':
                    dependency = this._invokeOne( function ( ext ) {

                        return ext.loadBufferView && ext.loadBufferView( index );

                    } );
                    break;

                case 'buffer':
                    dependency = this.loadBuffer( index );
                    break;

                case 'material':
                    dependency = this._invokeOne( function ( ext ) {

                        return ext.loadMaterial && ext.loadMaterial( index );

                    } );
                    break;

                case 'texture':
                    dependency = this._invokeOne( function ( ext ) {

                        return ext.loadTexture && ext.loadTexture( index );

                    } );
                    break;

                case 'skin':
                    dependency = this.loadSkin( index );
                    break;

                case 'animation':
                    dependency = this._invokeOne( function ( ext ) {

                        return ext.loadAnimation && ext.loadAnimation( index );

                    } );
                    break;

                case 'camera':
                    dependency = this.loadCamera( index );
                    break;

                default:
                    throw new Error( 'Unknown type: ' + type );

                }

                this.cache.add( cacheKey, dependency );

            }

            return dependency;

        }
        /**
         * Requests all dependencies of the specified type asynchronously, with caching.
         * @param {string} type
         * @return {Promise<Array<Object>>}
         */


        getDependencies( type ) {

            let dependencies = this.cache.get( type );

            if ( ! dependencies ) {

                const parser = this;
                const defs = this.json[ type + ( type === 'mesh' ? 'es' : 's' ) ] || [];
                dependencies = Promise.all( defs.map( function ( def, index ) {

                    return parser.getDependency( type, index );

                } ) );
                this.cache.add( type, dependencies );

            }

            return dependencies;

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
         * @param {number} bufferIndex
         * @return {Promise<ArrayBuffer>}
         */


        loadBuffer( bufferIndex ) {

            const bufferDef = this.json.buffers[ bufferIndex ];
            const loader = this.fileLoader;

            if ( bufferDef.type && bufferDef.type !== 'arraybuffer' ) {

                throw new Error( 'THREE.GLTFLoader: ' + bufferDef.type + ' buffer type is not supported.' );

            } // If present, GLB container is required to be the first buffer.


            if ( bufferDef.uri === undefined && bufferIndex === 0 ) {

                return Promise.resolve( this.extensions[ EXTENSIONS.KHR_BINARY_GLTF ].body );

            }

            const options = this.options;
            return new Promise( function ( resolve, reject ) {

                loader.load( THREE.LoaderUtils.resolveURL( bufferDef.uri, options.path ), resolve, undefined, function () {

                    reject( new Error( 'THREE.GLTFLoader: Failed to load buffer "' + bufferDef.uri + '".' ) );

                } );

            } );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
         * @param {number} bufferViewIndex
         * @return {Promise<ArrayBuffer>}
         */


        loadBufferView( bufferViewIndex ) {

            const bufferViewDef = this.json.bufferViews[ bufferViewIndex ];
            return this.getDependency( 'buffer', bufferViewDef.buffer ).then( function ( buffer ) {

                const byteLength = bufferViewDef.byteLength || 0;
                const byteOffset = bufferViewDef.byteOffset || 0;
                return buffer.slice( byteOffset, byteOffset + byteLength );

            } );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#accessors
         * @param {number} accessorIndex
         * @return {Promise<BufferAttribute|InterleavedBufferAttribute>}
         */


        loadAccessor( accessorIndex ) {

            const parser = this;
            const json = this.json;
            const accessorDef = this.json.accessors[ accessorIndex ];

            if ( accessorDef.bufferView === undefined && accessorDef.sparse === undefined ) {

                // Ignore empty accessors, which may be used to declare runtime
                // information about attributes coming from another source (e.g. Draco
                // compression extension).
                return Promise.resolve( null );

            }

            const pendingBufferViews = [];

            if ( accessorDef.bufferView !== undefined ) {

                pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.bufferView ) );

            } else {

                pendingBufferViews.push( null );

            }

            if ( accessorDef.sparse !== undefined ) {

                pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.indices.bufferView ) );
                pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.values.bufferView ) );

            }

            return Promise.all( pendingBufferViews ).then( function ( bufferViews ) {

                const bufferView = bufferViews[ 0 ];
                const itemSize = WEBGL_TYPE_SIZES[ accessorDef.type ];
                const TypedArray = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ]; // For VEC3: itemSize is 3, elementBytes is 4, itemBytes is 12.

                const elementBytes = TypedArray.BYTES_PER_ELEMENT;
                const itemBytes = elementBytes * itemSize;
                const byteOffset = accessorDef.byteOffset || 0;
                const byteStride = accessorDef.bufferView !== undefined ? json.bufferViews[ accessorDef.bufferView ].byteStride : undefined;
                const normalized = accessorDef.normalized === true;
                let array, bufferAttribute; // The buffer is not interleaved if the stride is the item size in bytes.

                if ( byteStride && byteStride !== itemBytes ) {

                    // Each "slice" of the buffer, as defined by 'count' elements of 'byteStride' bytes, gets its own THREE.InterleavedBuffer
                    // This makes sure that IBA.count reflects accessor.count properly
                    const ibSlice = Math.floor( byteOffset / byteStride );
                    const ibCacheKey = 'InterleavedBuffer:' + accessorDef.bufferView + ':' + accessorDef.componentType + ':' + ibSlice + ':' + accessorDef.count;
                    let ib = parser.cache.get( ibCacheKey );

                    if ( ! ib ) {

                        array = new TypedArray( bufferView, ibSlice * byteStride, accessorDef.count * byteStride / elementBytes ); // Integer parameters to IB/IBA are in array elements, not bytes.

                        ib = new THREE.InterleavedBuffer( array, byteStride / elementBytes );
                        parser.cache.add( ibCacheKey, ib );

                    }

                    bufferAttribute = new THREE.InterleavedBufferAttribute( ib, itemSize, byteOffset % byteStride / elementBytes, normalized );

                } else {

                    if ( bufferView === null ) {

                        array = new TypedArray( accessorDef.count * itemSize );

                    } else {

                        array = new TypedArray( bufferView, byteOffset, accessorDef.count * itemSize );

                    }

                    bufferAttribute = new THREE.BufferAttribute( array, itemSize, normalized );

                } // https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#sparse-accessors


                if ( accessorDef.sparse !== undefined ) {

                    const itemSizeIndices = WEBGL_TYPE_SIZES.SCALAR;
                    const TypedArrayIndices = WEBGL_COMPONENT_TYPES[ accessorDef.sparse.indices.componentType ];
                    const byteOffsetIndices = accessorDef.sparse.indices.byteOffset || 0;
                    const byteOffsetValues = accessorDef.sparse.values.byteOffset || 0;
                    const sparseIndices = new TypedArrayIndices( bufferViews[ 1 ], byteOffsetIndices, accessorDef.sparse.count * itemSizeIndices );
                    const sparseValues = new TypedArray( bufferViews[ 2 ], byteOffsetValues, accessorDef.sparse.count * itemSize );

                    if ( bufferView !== null ) {

                        // Avoid modifying the original ArrayBuffer, if the bufferView wasn't initialized with zeroes.
                        bufferAttribute = new THREE.BufferAttribute( bufferAttribute.array.slice(), bufferAttribute.itemSize, bufferAttribute.normalized );

                    }

                    for ( let i = 0, il = sparseIndices.length; i < il; i ++ ) {

                        const index = sparseIndices[ i ];
                        bufferAttribute.setX( index, sparseValues[ i * itemSize ] );
                        if ( itemSize >= 2 ) bufferAttribute.setY( index, sparseValues[ i * itemSize + 1 ] );
                        if ( itemSize >= 3 ) bufferAttribute.setZ( index, sparseValues[ i * itemSize + 2 ] );
                        if ( itemSize >= 4 ) bufferAttribute.setW( index, sparseValues[ i * itemSize + 3 ] );
                        if ( itemSize >= 5 ) throw new Error( 'THREE.GLTFLoader: Unsupported itemSize in sparse THREE.BufferAttribute.' );

                    }

                }

                return bufferAttribute;

            } );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#textures
         * @param {number} textureIndex
         * @return {Promise<THREE.Texture>}
         */


        loadTexture( textureIndex ) {

            const json = this.json;
            const options = this.options;
            const textureDef = json.textures[ textureIndex ];
            const sourceIndex = textureDef.source;
            const sourceDef = json.images[ sourceIndex ];
            let loader = this.textureLoader;

            if ( sourceDef.uri ) {

                const handler = options.manager.getHandler( sourceDef.uri );
                if ( handler !== null ) loader = handler;

            }

            return this.loadTextureImage( textureIndex, sourceIndex, loader );

        }

        loadTextureImage( textureIndex, sourceIndex, loader ) {

            const parser = this;
            const json = this.json;
            const textureDef = json.textures[ textureIndex ];
            const sourceDef = json.images[ sourceIndex ];
            const cacheKey = ( sourceDef.uri || sourceDef.bufferView ) + ':' + textureDef.sampler;

            if ( this.textureCache[ cacheKey ] ) {

                // See https://github.com/mrdoob/three.js/issues/21559.
                return this.textureCache[ cacheKey ];

            }

            const promise = this.loadImageSource( sourceIndex, loader ).then( function ( texture ) {

                texture.flipY = false;
                if ( textureDef.name ) texture.name = textureDef.name;
                const samplers = json.samplers || {};
                const sampler = samplers[ textureDef.sampler ] || {};
                texture.magFilter = WEBGL_FILTERS[ sampler.magFilter ] || THREE.LinearFilter;
                texture.minFilter = WEBGL_FILTERS[ sampler.minFilter ] || THREE.LinearMipmapLinearFilter;
                texture.wrapS = WEBGL_WRAPPINGS[ sampler.wrapS ] || THREE.RepeatWrapping;
                texture.wrapT = WEBGL_WRAPPINGS[ sampler.wrapT ] || THREE.RepeatWrapping;
                parser.associations.set( texture, {
                    textures: textureIndex
                } );
                return texture;

            } ).catch( function () {

                return null;

            } );
            this.textureCache[ cacheKey ] = promise;
            return promise;

        }

        loadImageSource( sourceIndex, loader ) {

            const parser = this;
            const json = this.json;
            const options = this.options;

            if ( this.sourceCache[ sourceIndex ] !== undefined ) {

                return this.sourceCache[ sourceIndex ].then( texture => texture.clone() );

            }

            const sourceDef = json.images[ sourceIndex ];
            const URL = self.URL || self.webkitURL;
            let sourceURI = sourceDef.uri || '';
            let isObjectURL = false;

            if ( sourceDef.bufferView !== undefined ) {

                // Load binary image data from bufferView, if provided.
                sourceURI = parser.getDependency( 'bufferView', sourceDef.bufferView ).then( function ( bufferView ) {

                    isObjectURL = true;
                    const blob = new Blob( [ bufferView ], {
                        type: sourceDef.mimeType
                    } );
                    sourceURI = URL.createObjectURL( blob );
                    return sourceURI;

                } );

            } else if ( sourceDef.uri === undefined ) {

                throw new Error( 'THREE.GLTFLoader: Image ' + sourceIndex + ' is missing URI and bufferView' );

            }

            const promise = Promise.resolve( sourceURI ).then( function ( sourceURI ) {

                return new Promise( function ( resolve, reject ) {

                    let onLoad = resolve;

                    if ( loader.isImageBitmapLoader === true ) {

                        onLoad = function ( imageBitmap ) {

                            const texture = new THREE.Texture( imageBitmap );
                            texture.needsUpdate = true;
                            resolve( texture );

                        };

                    }

                    loader.load( THREE.LoaderUtils.resolveURL( sourceURI, options.path ), onLoad, undefined, reject );

                } );

            } ).then( function ( texture ) {

                // Clean up resources and configure THREE.Texture.
                if ( isObjectURL === true ) {

                    URL.revokeObjectURL( sourceURI );

                }

                texture.userData.mimeType = sourceDef.mimeType || getImageURIMimeType( sourceDef.uri );
                return texture;

            } ).catch( function ( error ) {

                console.error( 'THREE.GLTFLoader: Couldn\'t load texture', sourceURI );
                throw error;

            } );
            this.sourceCache[ sourceIndex ] = promise;
            return promise;

        }
        /**
         * Asynchronously assigns a texture to the given material parameters.
         * @param {Object} materialParams
         * @param {string} mapName
         * @param {Object} mapDef
         * @return {Promise<Texture>}
         */


        assignTexture( materialParams, mapName, mapDef, encoding ) {

            const parser = this;
            return this.getDependency( 'texture', mapDef.index ).then( function ( texture ) {

                // Materials sample aoMap from UV set 1 and other maps from UV set 0 - this can't be configured
                // However, we will copy UV set 0 to UV set 1 on demand for aoMap
                if ( mapDef.texCoord !== undefined && mapDef.texCoord != 0 && ! ( mapName === 'aoMap' && mapDef.texCoord == 1 ) ) {

                    console.warn( 'THREE.GLTFLoader: Custom UV set ' + mapDef.texCoord + ' for texture ' + mapName + ' not yet supported.' );

                }

                if ( parser.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ] ) {

                    const transform = mapDef.extensions !== undefined ? mapDef.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ] : undefined;

                    if ( transform ) {

                        const gltfReference = parser.associations.get( texture );
                        texture = parser.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ].extendTexture( texture, transform );
                        parser.associations.set( texture, gltfReference );

                    }

                }

                if ( encoding !== undefined ) {

                    texture.encoding = encoding;

                }

                materialParams[ mapName ] = texture;
                return texture;

            } );

        }
        /**
         * Assigns final material to a THREE.Mesh, THREE.Line, or THREE.Points instance. The instance
         * already has a material (generated from the glTF material options alone)
         * but reuse of the same glTF material may require multiple threejs materials
         * to accommodate different primitive types, defines, etc. New materials will
         * be created if necessary, and reused from a cache.
         * @param  {Object3D} mesh THREE.Mesh, THREE.Line, or THREE.Points instance.
         */


        assignFinalMaterial( mesh ) {

            const geometry = mesh.geometry;
            let material = mesh.material;
            const useDerivativeTangents = geometry.attributes.tangent === undefined;
            const useVertexColors = geometry.attributes.color !== undefined;
            const useFlatShading = geometry.attributes.normal === undefined;

            if ( mesh.isPoints ) {

                const cacheKey = 'PointsMaterial:' + material.uuid;
                let pointsMaterial = this.cache.get( cacheKey );

                if ( ! pointsMaterial ) {

                    pointsMaterial = new THREE.PointsMaterial();
                    THREE.Material.prototype.copy.call( pointsMaterial, material );
                    pointsMaterial.color.copy( material.color );
                    pointsMaterial.map = material.map;
                    pointsMaterial.sizeAttenuation = false; // glTF spec says points should be 1px

                    this.cache.add( cacheKey, pointsMaterial );

                }

                material = pointsMaterial;

            } else if ( mesh.isLine ) {

                const cacheKey = 'LineBasicMaterial:' + material.uuid;
                let lineMaterial = this.cache.get( cacheKey );

                if ( ! lineMaterial ) {

                    lineMaterial = new THREE.LineBasicMaterial();
                    THREE.Material.prototype.copy.call( lineMaterial, material );
                    lineMaterial.color.copy( material.color );
                    this.cache.add( cacheKey, lineMaterial );

                }

                material = lineMaterial;

            } // Clone the material if it will be modified


            if ( useDerivativeTangents || useVertexColors || useFlatShading ) {

                let cacheKey = 'ClonedMaterial:' + material.uuid + ':';
                if ( material.isGLTFSpecularGlossinessMaterial ) cacheKey += 'specular-glossiness:';
                if ( useDerivativeTangents ) cacheKey += 'derivative-tangents:';
                if ( useVertexColors ) cacheKey += 'vertex-colors:';
                if ( useFlatShading ) cacheKey += 'flat-shading:';
                let cachedMaterial = this.cache.get( cacheKey );

                if ( ! cachedMaterial ) {

                    cachedMaterial = material.clone();
                    if ( useVertexColors ) cachedMaterial.vertexColors = true;
                    if ( useFlatShading ) cachedMaterial.flatShading = true;

                    if ( useDerivativeTangents ) {

                        // https://github.com/mrdoob/three.js/issues/11438#issuecomment-507003995
                        if ( cachedMaterial.normalScale ) cachedMaterial.normalScale.y *= - 1;
                        if ( cachedMaterial.clearcoatNormalScale ) cachedMaterial.clearcoatNormalScale.y *= - 1;

                    }

                    this.cache.add( cacheKey, cachedMaterial );
                    this.associations.set( cachedMaterial, this.associations.get( material ) );

                }

                material = cachedMaterial;

            } // workarounds for mesh and geometry


            if ( material.aoMap && geometry.attributes.uv2 === undefined && geometry.attributes.uv !== undefined ) {

                geometry.setAttribute( 'uv2', geometry.attributes.uv );

            }

            mesh.material = material;

        }

        getMaterialType() {

            return THREE.MeshStandardMaterial;

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials
         * @param {number} materialIndex
         * @return {Promise<Material>}
         */


        loadMaterial( materialIndex ) {

            const parser = this;
            const json = this.json;
            const extensions = this.extensions;
            const materialDef = json.materials[ materialIndex ];
            let materialType;
            const materialParams = {};
            const materialExtensions = materialDef.extensions || {};
            const pending = [];

            if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ] ) {

                const sgExtension = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ];
                materialType = sgExtension.getMaterialType();
                pending.push( sgExtension.extendParams( materialParams, materialDef, parser ) );

            } else if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ] ) {

                const kmuExtension = extensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ];
                materialType = kmuExtension.getMaterialType();
                pending.push( kmuExtension.extendParams( materialParams, materialDef, parser ) );

            } else {

                // Specification:
                // https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#metallic-roughness-material
                const metallicRoughness = materialDef.pbrMetallicRoughness || {};
                materialParams.color = new THREE.Color( 1.0, 1.0, 1.0 );
                materialParams.opacity = 1.0;

                if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

                    const array = metallicRoughness.baseColorFactor;
                    materialParams.color.fromArray( array );
                    materialParams.opacity = array[ 3 ];

                }

                if ( metallicRoughness.baseColorTexture !== undefined ) {

                    pending.push( parser.assignTexture( materialParams, 'map', metallicRoughness.baseColorTexture, THREE.sRGBEncoding ) );

                }

                materialParams.metalness = metallicRoughness.metallicFactor !== undefined ? metallicRoughness.metallicFactor : 1.0;
                materialParams.roughness = metallicRoughness.roughnessFactor !== undefined ? metallicRoughness.roughnessFactor : 1.0;

                if ( metallicRoughness.metallicRoughnessTexture !== undefined ) {

                    pending.push( parser.assignTexture( materialParams, 'metalnessMap', metallicRoughness.metallicRoughnessTexture ) );
                    pending.push( parser.assignTexture( materialParams, 'roughnessMap', metallicRoughness.metallicRoughnessTexture ) );

                }

                materialType = this._invokeOne( function ( ext ) {

                    return ext.getMaterialType && ext.getMaterialType( materialIndex );

                } );
                pending.push( Promise.all( this._invokeAll( function ( ext ) {

                    return ext.extendMaterialParams && ext.extendMaterialParams( materialIndex, materialParams );

                } ) ) );

            }

            if ( materialDef.doubleSided === true ) {

                materialParams.side = THREE.DoubleSide;

            }

            const alphaMode = materialDef.alphaMode || ALPHA_MODES.OPAQUE;

            if ( alphaMode === ALPHA_MODES.BLEND ) {

                materialParams.transparent = true; // See: https://github.com/mrdoob/three.js/issues/17706

                materialParams.depthWrite = false;

            } else {

                materialParams.transparent = false;

                if ( alphaMode === ALPHA_MODES.MASK ) {

                    materialParams.alphaTest = materialDef.alphaCutoff !== undefined ? materialDef.alphaCutoff : 0.5;

                }

            }

            if ( materialDef.normalTexture !== undefined && materialType !== THREE.MeshBasicMaterial ) {

                pending.push( parser.assignTexture( materialParams, 'normalMap', materialDef.normalTexture ) );
                materialParams.normalScale = new THREE.Vector2( 1, 1 );

                if ( materialDef.normalTexture.scale !== undefined ) {

                    const scale = materialDef.normalTexture.scale;
                    materialParams.normalScale.set( scale, scale );

                }

            }

            if ( materialDef.occlusionTexture !== undefined && materialType !== THREE.MeshBasicMaterial ) {

                pending.push( parser.assignTexture( materialParams, 'aoMap', materialDef.occlusionTexture ) );

                if ( materialDef.occlusionTexture.strength !== undefined ) {

                    materialParams.aoMapIntensity = materialDef.occlusionTexture.strength;

                }

            }

            if ( materialDef.emissiveFactor !== undefined && materialType !== THREE.MeshBasicMaterial ) {

                materialParams.emissive = new THREE.Color().fromArray( materialDef.emissiveFactor );

            }

            if ( materialDef.emissiveTexture !== undefined && materialType !== THREE.MeshBasicMaterial ) {

                pending.push( parser.assignTexture( materialParams, 'emissiveMap', materialDef.emissiveTexture, THREE.sRGBEncoding ) );

            }

            return Promise.all( pending ).then( function () {

                let material;

                if ( materialType === GLTFMeshStandardSGMaterial ) {

                    material = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ].createMaterial( materialParams );

                } else {

                    material = new materialType( materialParams );

                }

                if ( materialDef.name ) material.name = materialDef.name;
                assignExtrasToUserData( material, materialDef );
                parser.associations.set( material, {
                    materials: materialIndex
                } );
                if ( materialDef.extensions ) addUnknownExtensionsToUserData( extensions, material, materialDef );
                return material;

            } );

        }
        /** When THREE.Object3D instances are targeted by animation, they need unique names. */


        createUniqueName( originalName ) {

            const sanitizedName = THREE.PropertyBinding.sanitizeNodeName( originalName || '' );
            let name = sanitizedName;

            for ( let i = 1; this.nodeNamesUsed[ name ]; ++ i ) {

                name = sanitizedName + '_' + i;

            }

            this.nodeNamesUsed[ name ] = true;
            return name;

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#geometry
         *
         * Creates BufferGeometries from primitives.
         *
         * @param {Array<GLTF.Primitive>} primitives
         * @return {Promise<Array<BufferGeometry>>}
         */


        loadGeometries( primitives ) {

            const parser = this;
            const extensions = this.extensions;
            const cache = this.primitiveCache;

            function createDracoPrimitive( primitive ) {

                return extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ].decodePrimitive( primitive, parser ).then( function ( geometry ) {

                    return addPrimitiveAttributes( geometry, primitive, parser );

                } );

            }

            const pending = [];

            for ( let i = 0, il = primitives.length; i < il; i ++ ) {

                const primitive = primitives[ i ];
                const cacheKey = createPrimitiveKey( primitive ); // See if we've already created this geometry

                const cached = cache[ cacheKey ];

                if ( cached ) {

                    // Use the cached geometry if it exists
                    pending.push( cached.promise );

                } else {

                    let geometryPromise;

                    if ( primitive.extensions && primitive.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ] ) {

                        // Use DRACO geometry if available
                        geometryPromise = createDracoPrimitive( primitive );

                    } else {

                        // Otherwise create a new geometry
                        geometryPromise = addPrimitiveAttributes( new THREE.BufferGeometry(), primitive, parser );

                    } // Cache this geometry


                    cache[ cacheKey ] = {
                        primitive: primitive,
                        promise: geometryPromise
                    };
                    pending.push( geometryPromise );

                }

            }

            return Promise.all( pending );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#meshes
         * @param {number} meshIndex
         * @return {Promise<Group|Mesh|SkinnedMesh>}
         */


        loadMesh( meshIndex ) {

            const parser = this;
            const json = this.json;
            const extensions = this.extensions;
            const meshDef = json.meshes[ meshIndex ];
            const primitives = meshDef.primitives;
            const pending = [];

            for ( let i = 0, il = primitives.length; i < il; i ++ ) {

                const material = primitives[ i ].material === undefined ? createDefaultMaterial( this.cache ) : this.getDependency( 'material', primitives[ i ].material );
                pending.push( material );

            }

            pending.push( parser.loadGeometries( primitives ) );
            return Promise.all( pending ).then( function ( results ) {

                const materials = results.slice( 0, results.length - 1 );
                const geometries = results[ results.length - 1 ];
                const meshes = [];

                for ( let i = 0, il = geometries.length; i < il; i ++ ) {

                    const geometry = geometries[ i ];
                    const primitive = primitives[ i ]; // 1. create THREE.Mesh

                    let mesh;
                    const material = materials[ i ];

                    if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLES || primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP || primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN || primitive.mode === undefined ) {

                        // .isSkinnedMesh isn't in glTF spec. See ._markDefs()
                        mesh = meshDef.isSkinnedMesh === true ? new THREE.SkinnedMesh( geometry, material ) : new THREE.Mesh( geometry, material );

                        if ( mesh.isSkinnedMesh === true && ! mesh.geometry.attributes.skinWeight.normalized ) {

                            // we normalize floating point skin weight array to fix malformed assets (see #15319)
                            // it's important to skip this for non-float32 data since normalizeSkinWeights assumes non-normalized inputs
                            mesh.normalizeSkinWeights();

                        }

                        if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ) {

                            mesh.geometry = toTrianglesDrawMode( mesh.geometry, THREE.TriangleStripDrawMode );

                        } else if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ) {

                            mesh.geometry = toTrianglesDrawMode( mesh.geometry, THREE.TriangleFanDrawMode );

                        }

                    } else if ( primitive.mode === WEBGL_CONSTANTS.LINES ) {

                        mesh = new THREE.LineSegments( geometry, material );

                    } else if ( primitive.mode === WEBGL_CONSTANTS.LINE_STRIP ) {

                        mesh = new THREE.Line( geometry, material );

                    } else if ( primitive.mode === WEBGL_CONSTANTS.LINE_LOOP ) {

                        mesh = new THREE.LineLoop( geometry, material );

                    } else if ( primitive.mode === WEBGL_CONSTANTS.POINTS ) {

                        mesh = new THREE.Points( geometry, material );

                    } else {

                        throw new Error( 'THREE.GLTFLoader: Primitive mode unsupported: ' + primitive.mode );

                    }

                    if ( Object.keys( mesh.geometry.morphAttributes ).length > 0 ) {

                        updateMorphTargets( mesh, meshDef );

                    }

                    mesh.name = parser.createUniqueName( meshDef.name || 'mesh_' + meshIndex );
                    assignExtrasToUserData( mesh, meshDef );
                    if ( primitive.extensions ) addUnknownExtensionsToUserData( extensions, mesh, primitive );
                    parser.assignFinalMaterial( mesh );
                    meshes.push( mesh );

                }

                for ( let i = 0, il = meshes.length; i < il; i ++ ) {

                    parser.associations.set( meshes[ i ], {
                        meshes: meshIndex,
                        primitives: i
                    } );

                }

                if ( meshes.length === 1 ) {

                    return meshes[ 0 ];

                }

                const group = new THREE.Group();
                parser.associations.set( group, {
                    meshes: meshIndex
                } );

                for ( let i = 0, il = meshes.length; i < il; i ++ ) {

                    group.add( meshes[ i ] );

                }

                return group;

            } );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#cameras
         * @param {number} cameraIndex
         * @return {Promise<THREE.Camera>}
         */


        loadCamera( cameraIndex ) {

            let camera;
            const cameraDef = this.json.cameras[ cameraIndex ];
            const params = cameraDef[ cameraDef.type ];

            if ( ! params ) {

                console.warn( 'THREE.GLTFLoader: Missing camera parameters.' );
                return;

            }

            if ( cameraDef.type === 'perspective' ) {

                camera = new THREE.PerspectiveCamera( THREE.MathUtils.radToDeg( params.yfov ), params.aspectRatio || 1, params.znear || 1, params.zfar || 2e6 );

            } else if ( cameraDef.type === 'orthographic' ) {

                camera = new THREE.OrthographicCamera( - params.xmag, params.xmag, params.ymag, - params.ymag, params.znear, params.zfar );

            }

            if ( cameraDef.name ) camera.name = this.createUniqueName( cameraDef.name );
            assignExtrasToUserData( camera, cameraDef );
            return Promise.resolve( camera );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#skins
         * @param {number} skinIndex
         * @return {Promise<Object>}
         */


        loadSkin( skinIndex ) {

            const skinDef = this.json.skins[ skinIndex ];
            const skinEntry = {
                joints: skinDef.joints
            };

            if ( skinDef.inverseBindMatrices === undefined ) {

                return Promise.resolve( skinEntry );

            }

            return this.getDependency( 'accessor', skinDef.inverseBindMatrices ).then( function ( accessor ) {

                skinEntry.inverseBindMatrices = accessor;
                return skinEntry;

            } );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#animations
         * @param {number} animationIndex
         * @return {Promise<AnimationClip>}
         */


        loadAnimation( animationIndex ) {

            const json = this.json;
            const animationDef = json.animations[ animationIndex ];
            const pendingNodes = [];
            const pendingInputAccessors = [];
            const pendingOutputAccessors = [];
            const pendingSamplers = [];
            const pendingTargets = [];

            for ( let i = 0, il = animationDef.channels.length; i < il; i ++ ) {

                const channel = animationDef.channels[ i ];
                const sampler = animationDef.samplers[ channel.sampler ];
                const target = channel.target;
                const name = target.node !== undefined ? target.node : target.id; // NOTE: target.id is deprecated.

                const input = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.input ] : sampler.input;
                const output = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.output ] : sampler.output;
                pendingNodes.push( this.getDependency( 'node', name ) );
                pendingInputAccessors.push( this.getDependency( 'accessor', input ) );
                pendingOutputAccessors.push( this.getDependency( 'accessor', output ) );
                pendingSamplers.push( sampler );
                pendingTargets.push( target );

            }

            return Promise.all( [ Promise.all( pendingNodes ), Promise.all( pendingInputAccessors ), Promise.all( pendingOutputAccessors ), Promise.all( pendingSamplers ), Promise.all( pendingTargets ) ] ).then( function ( dependencies ) {

                const nodes = dependencies[ 0 ];
                const inputAccessors = dependencies[ 1 ];
                const outputAccessors = dependencies[ 2 ];
                const samplers = dependencies[ 3 ];
                const targets = dependencies[ 4 ];
                const tracks = [];

                for ( let i = 0, il = nodes.length; i < il; i ++ ) {

                    const node = nodes[ i ];
                    const inputAccessor = inputAccessors[ i ];
                    const outputAccessor = outputAccessors[ i ];
                    const sampler = samplers[ i ];
                    const target = targets[ i ];
                    if ( node === undefined ) continue;
                    node.updateMatrix();
                    node.matrixAutoUpdate = true;
                    let TypedKeyframeTrack;

                    switch ( PATH_PROPERTIES[ target.path ] ) {

                    case PATH_PROPERTIES.weights:
                        TypedKeyframeTrack = THREE.NumberKeyframeTrack;
                        break;

                    case PATH_PROPERTIES.rotation:
                        TypedKeyframeTrack = THREE.QuaternionKeyframeTrack;
                        break;

                    case PATH_PROPERTIES.position:
                    case PATH_PROPERTIES.scale:
                    default:
                        TypedKeyframeTrack = THREE.VectorKeyframeTrack;
                        break;

                    }

                    const targetName = node.name ? node.name : node.uuid;
                    const interpolation = sampler.interpolation !== undefined ? INTERPOLATION[ sampler.interpolation ] : THREE.InterpolateLinear;
                    const targetNames = [];

                    if ( PATH_PROPERTIES[ target.path ] === PATH_PROPERTIES.weights ) {

                        node.traverse( function ( object ) {

                            if ( object.morphTargetInfluences ) {

                                targetNames.push( object.name ? object.name : object.uuid );

                            }

                        } );

                    } else {

                        targetNames.push( targetName );

                    }

                    let outputArray = outputAccessor.array;

                    if ( outputAccessor.normalized ) {

                        const scale = getNormalizedComponentScale( outputArray.constructor );
                        const scaled = new Float32Array( outputArray.length );

                        for ( let j = 0, jl = outputArray.length; j < jl; j ++ ) {

                            scaled[ j ] = outputArray[ j ] * scale;

                        }

                        outputArray = scaled;

                    }

                    for ( let j = 0, jl = targetNames.length; j < jl; j ++ ) {

                        const track = new TypedKeyframeTrack( targetNames[ j ] + '.' + PATH_PROPERTIES[ target.path ], inputAccessor.array, outputArray, interpolation ); // Override interpolation with custom factory method.

                        if ( sampler.interpolation === 'CUBICSPLINE' ) {

                            track.createInterpolant = function InterpolantFactoryMethodGLTFCubicSpline( result ) {

                                // A CUBICSPLINE keyframe in glTF has three output values for each input value,
                                // representing inTangent, splineVertex, and outTangent. As a result, track.getValueSize()
                                // must be divided by three to get the interpolant's sampleSize argument.
                                const interpolantType = this instanceof THREE.QuaternionKeyframeTrack ? GLTFCubicSplineQuaternionInterpolant : GLTFCubicSplineInterpolant;
                                return new interpolantType( this.times, this.values, this.getValueSize() / 3, result );

                            }; // Mark as CUBICSPLINE. `track.getInterpolation()` doesn't support custom interpolants.


                            track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline = true;

                        }

                        tracks.push( track );

                    }

                }

                const name = animationDef.name ? animationDef.name : 'animation_' + animationIndex;
                return new THREE.AnimationClip( name, undefined, tracks );

            } );

        }

        createNodeMesh( nodeIndex ) {

            const json = this.json;
            const parser = this;
            const nodeDef = json.nodes[ nodeIndex ];
            if ( nodeDef.mesh === undefined ) return null;
            return parser.getDependency( 'mesh', nodeDef.mesh ).then( function ( mesh ) {

                const node = parser._getNodeRef( parser.meshCache, nodeDef.mesh, mesh ); // if weights are provided on the node, override weights on the mesh.


                if ( nodeDef.weights !== undefined ) {

                    node.traverse( function ( o ) {

                        if ( ! o.isMesh ) return;

                        for ( let i = 0, il = nodeDef.weights.length; i < il; i ++ ) {

                            o.morphTargetInfluences[ i ] = nodeDef.weights[ i ];

                        }

                    } );

                }

                return node;

            } );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#nodes-and-hierarchy
         * @param {number} nodeIndex
         * @return {Promise<Object3D>}
         */


        loadNode( nodeIndex ) {

            const json = this.json;
            const extensions = this.extensions;
            const parser = this;
            const nodeDef = json.nodes[ nodeIndex ]; // reserve node's name before its dependencies, so the root has the intended name.

            const nodeName = nodeDef.name ? parser.createUniqueName( nodeDef.name ) : '';
            return function () {

                const pending = [];

                const meshPromise = parser._invokeOne( function ( ext ) {

                    return ext.createNodeMesh && ext.createNodeMesh( nodeIndex );

                } );

                if ( meshPromise ) {

                    pending.push( meshPromise );

                }

                if ( nodeDef.camera !== undefined ) {

                    pending.push( parser.getDependency( 'camera', nodeDef.camera ).then( function ( camera ) {

                        return parser._getNodeRef( parser.cameraCache, nodeDef.camera, camera );

                    } ) );

                }

                parser._invokeAll( function ( ext ) {

                    return ext.createNodeAttachment && ext.createNodeAttachment( nodeIndex );

                } ).forEach( function ( promise ) {

                    pending.push( promise );

                } );

                return Promise.all( pending );

            }().then( function ( objects ) {

                let node; // .isBone isn't in glTF spec. See ._markDefs

                if ( nodeDef.isBone === true ) {

                    node = new THREE.Bone();

                } else if ( objects.length > 1 ) {

                    node = new THREE.Group();

                } else if ( objects.length === 1 ) {

                    node = objects[ 0 ];

                } else {

                    node = new THREE.Object3D();

                }

                if ( node !== objects[ 0 ] ) {

                    for ( let i = 0, il = objects.length; i < il; i ++ ) {

                        node.add( objects[ i ] );

                    }

                }

                if ( nodeDef.name ) {

                    node.userData.name = nodeDef.name;
                    node.name = nodeName;

                }

                assignExtrasToUserData( node, nodeDef );
                if ( nodeDef.extensions ) addUnknownExtensionsToUserData( extensions, node, nodeDef );

                if ( nodeDef.matrix !== undefined ) {

                    const matrix = new THREE.Matrix4();
                    matrix.fromArray( nodeDef.matrix );
                    node.applyMatrix4( matrix );

                } else {

                    if ( nodeDef.translation !== undefined ) {

                        node.position.fromArray( nodeDef.translation );

                    }

                    if ( nodeDef.rotation !== undefined ) {

                        node.quaternion.fromArray( nodeDef.rotation );

                    }

                    if ( nodeDef.scale !== undefined ) {

                        node.scale.fromArray( nodeDef.scale );

                    }

                }

                if ( ! parser.associations.has( node ) ) {

                    parser.associations.set( node, {} );

                }

                parser.associations.get( node ).nodes = nodeIndex;
                return node;

            } );

        }
        /**
         * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#scenes
         * @param {number} sceneIndex
         * @return {Promise<Group>}
         */


        loadScene( sceneIndex ) {

            const json = this.json;
            const extensions = this.extensions;
            const sceneDef = this.json.scenes[ sceneIndex ];
            const parser = this; // THREE.Loader returns THREE.Group, not Scene.
            // See: https://github.com/mrdoob/three.js/issues/18342#issuecomment-578981172

            const scene = new THREE.Group();
            if ( sceneDef.name ) scene.name = parser.createUniqueName( sceneDef.name );
            assignExtrasToUserData( scene, sceneDef );
            if ( sceneDef.extensions ) addUnknownExtensionsToUserData( extensions, scene, sceneDef );
            const nodeIds = sceneDef.nodes || [];
            const pending = [];

            for ( let i = 0, il = nodeIds.length; i < il; i ++ ) {

                pending.push( buildNodeHierarchy( nodeIds[ i ], scene, json, parser ) );

            }

            return Promise.all( pending ).then( function () {

                // Removes dangling associations, associations that reference a node that
                // didn't make it into the scene.
                const reduceAssociations = node => {

                    const reducedAssociations = new Map();

                    for ( const [ key, value ] of parser.associations ) {

                        if ( key instanceof THREE.Material || key instanceof THREE.Texture ) {

                            reducedAssociations.set( key, value );

                        }

                    }

                    node.traverse( node => {

                        const mappings = parser.associations.get( node );

                        if ( mappings != null ) {

                            reducedAssociations.set( node, mappings );

                        }

                    } );
                    return reducedAssociations;

                };

                parser.associations = reduceAssociations( scene );
                return scene;

            } );

        }

    }

    function buildNodeHierarchy( nodeId, parentObject, json, parser ) {

        const nodeDef = json.nodes[ nodeId ];
        return parser.getDependency( 'node', nodeId ).then( function ( node ) {

            if ( nodeDef.skin === undefined ) return node; // build skeleton here as well

            let skinEntry;
            return parser.getDependency( 'skin', nodeDef.skin ).then( function ( skin ) {

                skinEntry = skin;
                const pendingJoints = [];

                for ( let i = 0, il = skinEntry.joints.length; i < il; i ++ ) {

                    pendingJoints.push( parser.getDependency( 'node', skinEntry.joints[ i ] ) );

                }

                return Promise.all( pendingJoints );

            } ).then( function ( jointNodes ) {

                node.traverse( function ( mesh ) {

                    if ( ! mesh.isMesh ) return;
                    const bones = [];
                    const boneInverses = [];

                    for ( let j = 0, jl = jointNodes.length; j < jl; j ++ ) {

                        const jointNode = jointNodes[ j ];

                        if ( jointNode ) {

                            bones.push( jointNode );
                            const mat = new THREE.Matrix4();

                            if ( skinEntry.inverseBindMatrices !== undefined ) {

                                mat.fromArray( skinEntry.inverseBindMatrices.array, j * 16 );

                            }

                            boneInverses.push( mat );

                        } else {

                            console.warn( 'THREE.GLTFLoader: Joint "%s" could not be found.', skinEntry.joints[ j ] );

                        }

                    }

                    mesh.bind( new THREE.Skeleton( bones, boneInverses ), mesh.matrixWorld );

                } );
                return node;

            } );

        } ).then( function ( node ) {

            // build node hierachy
            parentObject.add( node );
            const pending = [];

            if ( nodeDef.children ) {

                const children = nodeDef.children;

                for ( let i = 0, il = children.length; i < il; i ++ ) {

                    const child = children[ i ];
                    pending.push( buildNodeHierarchy( child, node, json, parser ) );

                }

            }

            return Promise.all( pending );

        } );

    }
    /**
     * @param {BufferGeometry} geometry
     * @param {GLTF.Primitive} primitiveDef
     * @param {GLTFParser} parser
     */


    function computeBounds( geometry, primitiveDef, parser ) {

        const attributes = primitiveDef.attributes;
        const box = new THREE.Box3();

        if ( attributes.POSITION !== undefined ) {

            const accessor = parser.json.accessors[ attributes.POSITION ];
            const min = accessor.min;
            const max = accessor.max; // glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

            if ( min !== undefined && max !== undefined ) {

                box.set( new THREE.Vector3( min[ 0 ], min[ 1 ], min[ 2 ] ), new THREE.Vector3( max[ 0 ], max[ 1 ], max[ 2 ] ) );

                if ( accessor.normalized ) {

                    const boxScale = getNormalizedComponentScale( WEBGL_COMPONENT_TYPES[ accessor.componentType ] );
                    box.min.multiplyScalar( boxScale );
                    box.max.multiplyScalar( boxScale );

                }

            } else {

                console.warn( 'THREE.GLTFLoader: Missing min/max properties for accessor POSITION.' );
                return;

            }

        } else {

            return;

        }

        const targets = primitiveDef.targets;

        if ( targets !== undefined ) {

            const maxDisplacement = new THREE.Vector3();
            const vector = new THREE.Vector3();

            for ( let i = 0, il = targets.length; i < il; i ++ ) {

                const target = targets[ i ];

                if ( target.POSITION !== undefined ) {

                    const accessor = parser.json.accessors[ target.POSITION ];
                    const min = accessor.min;
                    const max = accessor.max; // glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

                    if ( min !== undefined && max !== undefined ) {

                        // we need to get max of absolute components because target weight is [-1,1]
                        vector.setX( Math.max( Math.abs( min[ 0 ] ), Math.abs( max[ 0 ] ) ) );
                        vector.setY( Math.max( Math.abs( min[ 1 ] ), Math.abs( max[ 1 ] ) ) );
                        vector.setZ( Math.max( Math.abs( min[ 2 ] ), Math.abs( max[ 2 ] ) ) );

                        if ( accessor.normalized ) {

                            const boxScale = getNormalizedComponentScale( WEBGL_COMPONENT_TYPES[ accessor.componentType ] );
                            vector.multiplyScalar( boxScale );

                        } // Note: this assumes that the sum of all weights is at most 1. This isn't quite correct - it's more conservative
                        // to assume that each target can have a max weight of 1. However, for some use cases - notably, when morph targets
                        // are used to implement key-frame animations and as such only two are active at a time - this results in very large
                        // boxes. So for now we make a box that's sometimes a touch too small but is hopefully mostly of reasonable size.


                        maxDisplacement.max( vector );

                    } else {

                        console.warn( 'THREE.GLTFLoader: Missing min/max properties for accessor POSITION.' );

                    }

                }

            } // As per comment above this box isn't conservative, but has a reasonable size for a very large number of morph targets.


            box.expandByVector( maxDisplacement );

        }

        geometry.boundingBox = box;
        const sphere = new THREE.Sphere();
        box.getCenter( sphere.center );
        sphere.radius = box.min.distanceTo( box.max ) / 2;
        geometry.boundingSphere = sphere;

    }
    /**
     * @param {BufferGeometry} geometry
     * @param {GLTF.Primitive} primitiveDef
     * @param {GLTFParser} parser
     * @return {Promise<BufferGeometry>}
     */


    function addPrimitiveAttributes( geometry, primitiveDef, parser ) {

        const attributes = primitiveDef.attributes;
        const pending = [];

        function assignAttributeAccessor( accessorIndex, attributeName ) {

            return parser.getDependency( 'accessor', accessorIndex ).then( function ( accessor ) {

                geometry.setAttribute( attributeName, accessor );

            } );

        }

        for ( const gltfAttributeName in attributes ) {

            const threeAttributeName = ATTRIBUTES[ gltfAttributeName ] || gltfAttributeName.toLowerCase(); // Skip attributes already provided by e.g. Draco extension.

            if ( threeAttributeName in geometry.attributes ) continue;
            pending.push( assignAttributeAccessor( attributes[ gltfAttributeName ], threeAttributeName ) );

        }

        if ( primitiveDef.indices !== undefined && ! geometry.index ) {

            const accessor = parser.getDependency( 'accessor', primitiveDef.indices ).then( function ( accessor ) {

                geometry.setIndex( accessor );

            } );
            pending.push( accessor );

        }

        assignExtrasToUserData( geometry, primitiveDef );
        computeBounds( geometry, primitiveDef, parser );
        return Promise.all( pending ).then( function () {

            return primitiveDef.targets !== undefined ? addMorphTargets( geometry, primitiveDef.targets, parser ) : geometry;

        } );

    }
    /**
     * @param {BufferGeometry} geometry
     * @param {Number} drawMode
     * @return {BufferGeometry}
     */


    function toTrianglesDrawMode( geometry, drawMode ) {

        let index = geometry.getIndex(); // generate index if not present

        if ( index === null ) {

            const indices = [];
            const position = geometry.getAttribute( 'position' );

            if ( position !== undefined ) {

                for ( let i = 0; i < position.count; i ++ ) {

                    indices.push( i );

                }

                geometry.setIndex( indices );
                index = geometry.getIndex();

            } else {

                console.error( 'THREE.GLTFLoader.toTrianglesDrawMode(): Undefined position attribute. Processing not possible.' );
                return geometry;

            }

        } //


        const numberOfTriangles = index.count - 2;
        const newIndices = [];

        if ( drawMode === THREE.TriangleFanDrawMode ) {

            // gl.TRIANGLE_FAN
            for ( let i = 1; i <= numberOfTriangles; i ++ ) {

                newIndices.push( index.getX( 0 ) );
                newIndices.push( index.getX( i ) );
                newIndices.push( index.getX( i + 1 ) );

            }

        } else {

            // gl.TRIANGLE_STRIP
            for ( let i = 0; i < numberOfTriangles; i ++ ) {

                if ( i % 2 === 0 ) {

                    newIndices.push( index.getX( i ) );
                    newIndices.push( index.getX( i + 1 ) );
                    newIndices.push( index.getX( i + 2 ) );

                } else {

                    newIndices.push( index.getX( i + 2 ) );
                    newIndices.push( index.getX( i + 1 ) );
                    newIndices.push( index.getX( i ) );

                }

            }

        }

        if ( newIndices.length / 3 !== numberOfTriangles ) {

            console.error( 'THREE.GLTFLoader.toTrianglesDrawMode(): Unable to generate correct amount of triangles.' );

        } // build final geometry


        const newGeometry = geometry.clone();
        newGeometry.setIndex( newIndices );
        return newGeometry;

    }

    THREE.GLTFLoader = GLTFLoader;

} )();