text: /**
   * @author mrdoob / http://mrdoob.com/
   */
  
  THREE.BufferGeometryUtils = {
  
  	computeTangents: function ( geometry ) {
  
  		var index = geometry.index;
  		var attributes = geometry.attributes;
  
  		// based on http://www.terathon.com/code/tangent.html
  		// (per vertex tangents)
  
  		if ( index === null ||
  			 attributes.position === undefined ||
  			 attributes.normal === undefined ||
  			 attributes.uv === undefined ) {
  
  			console.warn( 'THREE.BufferGeometry: Missing required attributes (index, position, normal or uv) in BufferGeometry.computeTangents()' );
  			return;
  
  		}
  
  		var indices = index.array;
  		var positions = attributes.position.array;
  		var normals = attributes.normal.array;
  		var uvs = attributes.uv.array;
  
  		var nVertices = positions.length / 3;
  
  		if ( attributes.tangent === undefined ) {
  
  			geometry.addAttribute( 'tangent', new THREE.BufferAttribute( new Float32Array( 4 * nVertices ), 4 ) );
  
  		}
  
  		var tangents = attributes.tangent.array;
  
  		var tan1 = [], tan2 = [];
  
  		for ( var i = 0; i < nVertices; i ++ ) {
  
  			tan1[ i ] = new THREE.Vector3();
  			tan2[ i ] = new THREE.Vector3();
  
  		}
  
  		var vA = new THREE.Vector3(),
  			vB = new THREE.Vector3(),
  			vC = new THREE.Vector3(),
  
  			uvA = new THREE.Vector2(),
  			uvB = new THREE.Vector2(),
  			uvC = new THREE.Vector2(),
  
  			sdir = new THREE.Vector3(),
  			tdir = new THREE.Vector3();
  
  		function handleTriangle( a, b, c ) {
  
  			vA.fromArray( positions, a * 3 );
  			vB.fromArray( positions, b * 3 );
  			vC.fromArray( positions, c * 3 );
  
  			uvA.fromArray( uvs, a * 2 );
  			uvB.fromArray( uvs, b * 2 );
  			uvC.fromArray( uvs, c * 2 );
  
  			var x1 = vB.x - vA.x;
  			var x2 = vC.x - vA.x;
  
  			var y1 = vB.y - vA.y;
  			var y2 = vC.y - vA.y;
  
  			var z1 = vB.z - vA.z;
  			var z2 = vC.z - vA.z;
  
  			var s1 = uvB.x - uvA.x;
  			var s2 = uvC.x - uvA.x;
  
  			var t1 = uvB.y - uvA.y;
  			var t2 = uvC.y - uvA.y;
  
  			var r = 1.0 / ( s1 * t2 - s2 * t1 );
  
  			sdir.set(
  				( t2 * x1 - t1 * x2 ) * r,
  				( t2 * y1 - t1 * y2 ) * r,
  				( t2 * z1 - t1 * z2 ) * r
  			);
  
  			tdir.set(
  				( s1 * x2 - s2 * x1 ) * r,
  				( s1 * y2 - s2 * y1 ) * r,
  				( s1 * z2 - s2 * z1 ) * r
  			);
  
  			tan1[ a ].add( sdir );
  			tan1[ b ].add( sdir );
  			tan1[ c ].add( sdir );
  
  			tan2[ a ].add( tdir );
  			tan2[ b ].add( tdir );
  			tan2[ c ].add( tdir );
  
  		}
  
  		var groups = geometry.groups;
  
  		if ( groups.length === 0 ) {
  
  			groups = [ {
  				start: 0,
  				count: indices.length
  			} ];
  
  		}
  
  		for ( var i = 0, il = groups.length; i < il; ++ i ) {
  
  			var group = groups[ i ];
  
  			var start = group.start;
  			var count = group.count;
  
  			for ( var j = start, jl = start + count; j < jl; j += 3 ) {
  
  				handleTriangle(
  					indices[ j + 0 ],
  					indices[ j + 1 ],
  					indices[ j + 2 ]
  				);
  
  			}
  
  		}
  
  		var tmp = new THREE.Vector3(), tmp2 = new THREE.Vector3();
  		var n = new THREE.Vector3(), n2 = new THREE.Vector3();
  		var w, t, test;
  
  		function handleVertex( v ) {
  
  			n.fromArray( normals, v * 3 );
  			n2.copy( n );
  
  			t = tan1[ v ];
  
  			// Gram-Schmidt orthogonalize
  
  			tmp.copy( t );
  			tmp.sub( n.multiplyScalar( n.dot( t ) ) ).normalize();
  
  			// Calculate handedness
  
  			tmp2.crossVectors( n2, t );
  			test = tmp2.dot( tan2[ v ] );
  			w = ( test < 0.0 ) ? - 1.0 : 1.0;
  
  			tangents[ v * 4 ] = tmp.x;
  			tangents[ v * 4 + 1 ] = tmp.y;
  			tangents[ v * 4 + 2 ] = tmp.z;
  			tangents[ v * 4 + 3 ] = w;
  
  		}
  
  		for ( var i = 0, il = groups.length; i < il; ++ i ) {
  
  			var group = groups[ i ];
  
  			var start = group.start;
  			var count = group.count;
  
  			for ( var j = start, jl = start + count; j < jl; j += 3 ) {
  
  				handleVertex( indices[ j + 0 ] );
  				handleVertex( indices[ j + 1 ] );
  				handleVertex( indices[ j + 2 ] );
  
  			}
  
  		}
  
  	},
  
  	/**
  	 * @param  {Array<THREE.BufferGeometry>} geometries
  	 * @param  {Boolean} useGroups
  	 * @return {THREE.BufferGeometry}
  	 */
  	mergeBufferGeometries: function ( geometries, useGroups ) {
  
  		var isIndexed = geometries[ 0 ].index !== null;
  
  		var attributesUsed = new Set( Object.keys( geometries[ 0 ].attributes ) );
  		var morphAttributesUsed = new Set( Object.keys( geometries[ 0 ].morphAttributes ) );
  
  		var attributes = {};
  		var morphAttributes = {};
  
  		var mergedGeometry = new THREE.BufferGeometry();
  
  		var offset = 0;
  
  		for ( var i = 0; i < geometries.length; ++ i ) {
  
  			var geometry = geometries[ i ];
  
  			// ensure that all geometries are indexed, or none
  
  			if ( isIndexed !== ( geometry.index !== null ) ) return null;
  
  			// gather attributes, exit early if they're different
  
  			for ( var name in geometry.attributes ) {
  
  				if ( ! attributesUsed.has( name ) ) return null;
  
  				if ( attributes[ name ] === undefined ) attributes[ name ] = [];
  
  				attributes[ name ].push( geometry.attributes[ name ] );
  
  			}
  
  			// gather morph attributes, exit early if they're different
  
  			for ( var name in geometry.morphAttributes ) {
  
  				if ( ! morphAttributesUsed.has( name ) ) return null;
  
  				if ( morphAttributes[ name ] === undefined ) morphAttributes[ name ] = [];
  
  				morphAttributes[ name ].push( geometry.morphAttributes[ name ] );
  
  			}
  
  			// gather .userData
  
  			mergedGeometry.userData.mergedUserData = mergedGeometry.userData.mergedUserData || [];
  			mergedGeometry.userData.mergedUserData.push( geometry.userData );
  
  			if ( useGroups ) {
  
  				var count;
  
  				if ( isIndexed ) {
  
  					count = geometry.index.count;
  
  				} else if ( geometry.attributes.position !== undefined ) {
  
  					count = geometry.attributes.position.count;
  
  				} else {
  
  					return null;
  
  				}
  
  				mergedGeometry.addGroup( offset, count, i );
  
  				offset += count;
  
  			}
  
  		}
  
  		// merge indices
  
  		if ( isIndexed ) {
  
  			var indexOffset = 0;
  			var mergedIndex = [];
  
  			for ( var i = 0; i < geometries.length; ++ i ) {
  
  				var index = geometries[ i ].index;
  
  				for ( var j = 0; j < index.count; ++ j ) {
  
  					mergedIndex.push( index.getX( j ) + indexOffset );
  
  				}
  
  				indexOffset += geometries[ i ].attributes.position.count;
  
  			}
  
  			mergedGeometry.setIndex( mergedIndex );
  
  		}
  
  		// merge attributes
  
  		for ( var name in attributes ) {
  
  			var mergedAttribute = this.mergeBufferAttributes( attributes[ name ] );
  
  			if ( ! mergedAttribute ) return null;
  
  			mergedGeometry.addAttribute( name, mergedAttribute );
  
  		}
  
  		// merge morph attributes
  
  		for ( var name in morphAttributes ) {
  
  			var numMorphTargets = morphAttributes[ name ][ 0 ].length;
  
  			if ( numMorphTargets === 0 ) break;
  
  			mergedGeometry.morphAttributes = mergedGeometry.morphAttributes || {};
  			mergedGeometry.morphAttributes[ name ] = [];
  
  			for ( var i = 0; i < numMorphTargets; ++ i ) {
  
  				var morphAttributesToMerge = [];
  
  				for ( var j = 0; j < morphAttributes[ name ].length; ++ j ) {
  
  					morphAttributesToMerge.push( morphAttributes[ name ][ j ][ i ] );
  
  				}
  
  				var mergedMorphAttribute = this.mergeBufferAttributes( morphAttributesToMerge );
  
  				if ( ! mergedMorphAttribute ) return null;
  
  				mergedGeometry.morphAttributes[ name ].push( mergedMorphAttribute );
  
  			}
  
  		}
  
  		return mergedGeometry;
  
  	},
  
  	/**
  	 * @param {Array<THREE.BufferAttribute>} attributes
  	 * @return {THREE.BufferAttribute}
  	 */
  	mergeBufferAttributes: function ( attributes ) {
  
  		var TypedArray;
  		var itemSize;
  		var normalized;
  		var arrayLength = 0;
  
  		for ( var i = 0; i < attributes.length; ++ i ) {
  
  			var attribute = attributes[ i ];
  
  			if ( attribute.isInterleavedBufferAttribute ) return null;
  
  			if ( TypedArray === undefined ) TypedArray = attribute.array.constructor;
  			if ( TypedArray !== attribute.array.constructor ) return null;
  
  			if ( itemSize === undefined ) itemSize = attribute.itemSize;
  			if ( itemSize !== attribute.itemSize ) return null;
  
  			if ( normalized === undefined ) normalized = attribute.normalized;
  			if ( normalized !== attribute.normalized ) return null;
  
  			arrayLength += attribute.array.length;
  
  		}
  
  		var array = new TypedArray( arrayLength );
  		var offset = 0;
  
  		for ( var i = 0; i < attributes.length; ++ i ) {
  
  			array.set( attributes[ i ].array, offset );
  
  			offset += attributes[ i ].array.length;
  
  		}
  
  		return new THREE.BufferAttribute( array, itemSize, normalized );
  
  	},
  
  	/**
  	 * @param {Array<THREE.BufferAttribute>} attributes
  	 * @return {Array<THREE.InterleavedBufferAttribute>}
  	 */
  	interleaveAttributes: function ( attributes ) {
  
  		// Interleaves the provided attributes into an InterleavedBuffer and returns
  		// a set of InterleavedBufferAttributes for each attribute
  		var TypedArray;
  		var arrayLength = 0;
  		var stride = 0;
  
  		// calculate the the length and type of the interleavedBuffer
  		for ( var i = 0, l = attributes.length; i < l; ++ i ) {
  
  			var attribute = attributes[ i ];
  
  			if ( TypedArray === undefined ) TypedArray = attribute.array.constructor;
  			if ( TypedArray !== attribute.array.constructor ) {
  
  				console.warn( 'AttributeBuffers of different types cannot be interleaved' );
  				return null;
  
  			}
  
  			arrayLength += attribute.array.length;
  			stride += attribute.itemSize;
  
  		}
  
  		// Create the set of buffer attributes
  		var interleavedBuffer = new THREE.InterleavedBuffer( new TypedArray( arrayLength ), stride );
  		var offset = 0;
  		var res = [];
  		var getters = [ 'getX', 'getY', 'getZ', 'getW' ];
  		var setters = [ 'setX', 'setY', 'setZ', 'setW' ];
  
  		for ( var j = 0, l = attributes.length; j < l; j ++ ) {
  
  			var attribute = attributes[ j ];
  			var itemSize = attribute.itemSize;
  			var count = attribute.count;
  			var iba = new THREE.InterleavedBufferAttribute( interleavedBuffer, itemSize, offset, attribute.normalized );
  			res.push( iba );
  
  			offset += itemSize;
  
  			// Move the data for each attribute into the new interleavedBuffer
  			// at the appropriate offset
  			for ( var c = 0; c < count; c ++ ) {
  
  				for ( var k = 0; k < itemSize; k ++ ) {
  
  					iba[ setters[ k ] ]( c, attribute[ getters[ k ] ]( c ) );
  
  				}
  
  			}
  
  		}
  
  		return res;
  
  	},
  
  	/**
  	 * @param {Array<THREE.BufferGeometry>} geometry
  	 * @return {number}
  	 */
  	estimateBytesUsed: function ( geometry ) {
  
  		// Return the estimated memory used by this geometry in bytes
  		// Calculate using itemSize, count, and BYTES_PER_ELEMENT to account
  		// for InterleavedBufferAttributes.
  		var mem = 0;
  		for ( var name in geometry.attributes ) {
  
  			var attr = geometry.getAttribute( name );
  			mem += attr.count * attr.itemSize * attr.array.BYTES_PER_ELEMENT;
  
  		}
  
  		var indices = geometry.getIndex();
  		mem += indices ? indices.count * indices.itemSize * indices.array.BYTES_PER_ELEMENT : 0;
  		return mem;
  
  	},
  
  	/**
  	 * @param {THREE.BufferGeometry} geometry
  	 * @param {number} tolerance
  	 * @return {THREE.BufferGeometry>}
  	 */
  	mergeVertices: function ( geometry, tolerance = 1e-4 ) {
  
  		tolerance = Math.max( tolerance, Number.EPSILON );
  
  		// Generate an index buffer if the geometry doesn't have one, or optimize it
  		// if it's already available.
  		var hashToIndex = {};
  		var indices = geometry.getIndex();
  		var positions = geometry.getAttribute( 'position' );
  		var vertexCount = indices ? indices.count : positions.count;
  
  		// next value for triangle indices
  		var nextIndex = 0;
  
  		// attributes and new attribute arrays
  		var attributeNames = Object.keys( geometry.attributes );
  		var attrArrays = {};
  		var morphAttrsArrays = {};
  		var newIndices = [];
  		var getters = [ 'getX', 'getY', 'getZ', 'getW' ];
  
  		// initialize the arrays
  		for ( var i = 0, l = attributeNames.length; i < l; i ++ ) {
  			var name = attributeNames[ i ];
  
  			attrArrays[ name ] = [];
  
  			var morphAttr = geometry.morphAttributes[ name ];
  			if ( morphAttr ) {
  
  				morphAttrsArrays[ name ] = new Array( morphAttr.length ).fill().map( () => [] );
  
  			}
  
  		}
  
  		// convert the error tolerance to an amount of decimal places to truncate to
  		var decimalShift = Math.log10( 1 / tolerance );
  		var shiftMultiplier = Math.pow( 10, decimalShift );
  		for ( var i = 0; i < vertexCount; i ++ ) {
  
  			var index = indices ? indices.getX( i ) : i;
  
  			// Generate a hash for the vertex attributes at the current index 'i'
  			var hash = '';
  			for ( var j = 0, l = attributeNames.length; j < l; j ++ ) {
  
  				var name = attributeNames[ j ];
  				var attribute = geometry.getAttribute( name );
  				var itemSize = attribute.itemSize;
  
  				for ( var k = 0; k < itemSize; k ++ ) {
  
  					// double tilde truncates the decimal value
  					hash += `${ ~ ~ ( attribute[ getters[ k ] ]( index ) * shiftMultiplier ) },`;
  
  				}
  
  			}
  
  			// Add another reference to the vertex if it's already
  			// used by another index
  			if ( hash in hashToIndex ) {
  
  				newIndices.push( hashToIndex[ hash ] );
  
  			} else {
  
  				// copy data to the new index in the attribute arrays
  				for ( var j = 0, l = attributeNames.length; j < l; j ++ ) {
  
  					var name = attributeNames[ j ];
  					var attribute = geometry.getAttribute( name );
  					var morphAttr = geometry.morphAttributes[ name ];
  					var itemSize = attribute.itemSize;
  					var newarray = attrArrays[ name ];
  					var newMorphArrays = morphAttrsArrays[ name ];
  
  					for ( var k = 0; k < itemSize; k ++ ) {
  
  						var getterFunc = getters[ k ];
  						newarray.push( attribute[ getterFunc ]( index ) );
  
  						if ( morphAttr ) {
  
  							for ( var m = 0, ml = morphAttr.length; m < ml; m ++ ) {
  
  								newMorphArrays[ m ].push( morphAttr[ m ][ getterFunc ]( index ) );
  
  							}
  
  						}
  
  					}
  
  				}
  
  				hashToIndex[ hash ] = nextIndex;
  				newIndices.push( nextIndex );
  				nextIndex ++;
  
  			}
  
  		}
  
  		// Generate typed arrays from new attribute arrays and update
  		// the attributeBuffers
  		const result = geometry.clone();
  		for ( var i = 0, l = attributeNames.length; i < l; i ++ ) {
  
  			var name = attributeNames[ i ];
  			var oldAttribute = geometry.getAttribute( name );
  			var attribute;
  
  			var buffer = new oldAttribute.array.constructor( attrArrays[ name ] );
  			if ( oldAttribute.isInterleavedBufferAttribute ) {
  
  				attribute = new THREE.BufferAttribute( buffer, oldAttribute.itemSize, oldAttribute.itemSize );
  
  			} else {
  
  				attribute = geometry.getAttribute( name ).clone();
  				attribute.setArray( buffer );
  
  			}
  
  			result.addAttribute( name, attribute );
  
  			// Update the attribute arrays
  			if ( name in morphAttrsArrays ) {
  
  				for ( var j = 0; j < morphAttrsArrays[ name ].length; j ++ ) {
  
  					var morphAttribute = geometry.morphAttributes[ name ][ j ].clone();
  					morphAttribute.setArray( new morphAttribute.array.constructor( morphAttrsArrays[ name ][ j ] ) );
  					result.morphAttributes[ name ][ j ] = morphAttribute;
  
  				}
  
  			}
  
  		}
  
  		// Generate an index buffer typed array
  		var cons = Uint8Array;
  		if ( newIndices.length >= Math.pow( 2, 8 ) ) cons = Uint16Array;
  		if ( newIndices.length >= Math.pow( 2, 16 ) ) cons = Uint32Array;
  
  		var newIndexBuffer = new cons( newIndices );
  		var newIndices = null;
  		if ( indices === null ) {
  
  			newIndices = new THREE.BufferAttribute( newIndexBuffer, 1 );
  
  		} else {
  
  			newIndices = geometry.getIndex().clone();
  			newIndices.setArray( newIndexBuffer );
  
  		}
  
  		result.setIndex( newIndices );
  
  		return result;
  
  	}
  
  };
  