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 );

} );

} );

}

}