<!-- AVATAR-FORGE · part 53 -->
angles having coincident or colinear vertices

			if ( ! isFinite( r ) ) return;

			sdir.copy( vB ).multiplyScalar( uvC.y ).addScaledVector( vC, - uvB.y ).multiplyScalar( r );
			tdir.copy( vC ).multiplyScalar( uvB.x ).addScaledVector( vB, - uvC.x ).multiplyScalar( 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 );

		}

		let groups = this.groups;

		if ( groups.length === 0 ) {

			groups = [ {
				start: 0,
				count: index.count
			} ];

		}

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

			const group = groups[ i ];

			const start = group.start;
			const count = group.count;

			for ( let j = start, jl = start + count; j < jl; j += 3 ) {

				handleTriangle(
					index.getX( j + 0 ),
					index.getX( j + 1 ),
					index.getX( j + 2 )
				);

			}

		}

		const tmp = new Vector3(), tmp2 = new Vector3();
		const n = new Vector3(), n2 = new Vector3();

		function handleVertex( v ) {

			n.fromBufferAttribute( normalAttribute, v );
			n2.copy( n );

			const t = tan1[ v ];

			// Gram-Schmidt orthogonalize

			tmp.copy( t );
			tmp.sub( n.multiplyScalar( n.dot( t ) ) ).normalize();

			// Calculate handedness

			tmp2.crossVectors( n2, t );
			const test = tmp2.dot( tan2[ v ] );
			const w = ( test < 0.0 ) ? - 1.0 : 1.0;

			tangentAttribute.setXYZW( v, tmp.x, tmp.y, tmp.z, w );

		}

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

			const group = groups[ i ];

			const start = group.start;
			const count = group.count;

			for ( let j = start, jl = start + count; j < jl; j += 3 ) {

				handleVertex( index.getX( j + 0 ) );
				handleVertex( index.getX( j + 1 ) );
				handleVertex( index.getX( j + 2 ) );

			}

		}

	}

	computeVertexNormals() {

		const index = this.index;
		const positionAttribute = this.getAttribute( 'position' );

		if ( positionAttribute !== undefined ) {

			let normalAttribute = this.getAttribute( 'normal' );

			if ( normalAttribute === undefined ) {

				normalAttribute = new BufferAttribute( new Float32Array( positionAttribute.count * 3 ), 3 );
				this.setAttribute( 'normal', normalAttribute );

			} else {

				// reset existing normals to zero

				for ( let i = 0, il = normalAttribute.count; i < il; i ++ ) {

					normalAttribute.setXYZ( i, 0, 0, 0 );

				}

			}

			const pA = new Vector3(), pB = new Vector3(), pC = new Vector3();
			const nA = new Vector3(), nB = new Vector3(), nC = new Vector3();
			const cb = new Vector3(), ab = new Vector3();

			// indexed elements

			if ( index ) {

				for ( let i = 0, il = index.count; i < il; i += 3 ) {

					const vA = index.getX( i + 0 );
					const vB = index.getX( i + 1 );
					const vC = index.getX( i + 2 );

					pA.fromBufferAttribute( positionAttribute, vA );
					pB.fromBufferAttribute( positionAttribute, vB );
					pC.fromBufferAttribute( positionAttribute, vC );

					cb.subVectors( pC, pB );
					ab.subVectors( pA, pB );
					cb.cross( ab );

					nA.fromBufferAttribute( normalAttribute, vA );
					nB.fromBufferAttribute( normalAttribute, vB );
					nC.fromBufferAttribute( normalAttribute, vC );

					nA.add( cb );
					nB.add( cb );
					nC.add( cb );

					normalAttribute.setXYZ( vA, nA.x, nA.y, nA.z );
					normalAttribute.setXYZ( vB, nB.x, nB.y, nB.z );
					normalAttribute.setXYZ( vC, nC.x, nC.y, nC.z );

				}

			} else {

				// non-indexed elements (unconnected triangle soup)

				for ( let i = 0, il = positionAttribute.count; i < il; i += 3 ) {

					pA.fromBufferAttribute( positionAttribute, i + 0 );
					pB.fromBufferAttribute( positionAttribute, i + 1 );
					pC.fromBufferAttribute( positionAttribute, i + 2 );

					cb.subVectors( pC, pB );
					ab.subVectors( pA, pB );
					cb.cross( ab );

					normalAttribute.setXYZ( i + 0, cb.x, cb.y, cb.z );
					normalAttribute.setXYZ( i + 1, cb.x, cb.y, cb.z );
					normalAttribute.setXYZ( i + 2, cb.x, cb.y, cb.z );

				}

			}

			this.normalizeNormals();

			normalAttribute.needsUpdate = true;

		}

	}

	normalizeNormals() {

		const normals = this.attributes.normal;

		for ( let i = 0, il = normals.count; i < il; i ++ ) {

			_vector$8.fromBufferAttribute( normals, i );

			_vector$8.normalize();

			normals.setXYZ( i, _vector$8.x, _vector$8.y, _vector$8.z );

		}

	}

	toNonIndexed() {

		function convertBufferAttribute( attribute, indices ) {

			const array = attribute.array;
			const itemSize = attribute.itemSize;
			const normalized = attribute.normalized;

			const array2 = new array.constructor( indices.length * itemSize );

			let index = 0, index2 = 0;

			for ( let i = 0, l = indices.length; i < l; i ++ ) {

				if ( attribute.isInterleavedBufferAttribute ) {

					index = indices[ i ] * attribute.data.stride + attribute.offset;

				} else {

					index = indices[ i ] * itemSize;

				}

				for ( let j = 0; j < itemSize; j ++ ) {

					array2[ index2 ++ ] = array[ index ++ ];

				}