constructor( radius = 1, tube = 0.4, radialSegments = 12, tubularSegments = 48, arc = Math.PI * 2 ) {

		super();

		this.type = 'TorusGeometry';

		/**
		 * Holds the constructor parameters that have been
		 * used to generate the geometry. Any modification
		 * after instantiation does not change the geometry.
		 *
		 * @type {Object}
		 */
		this.parameters = {
			radius: radius,
			tube: tube,
			radialSegments: radialSegments,
			tubularSegments: tubularSegments,
			arc: arc
		};

		radialSegments = Math.floor( radialSegments );
		tubularSegments = Math.floor( tubularSegments );

		// buffers

		const indices = [];
		const vertices = [];
		const normals = [];
		const uvs = [];

		// helper variables

		const center = new Vector3();
		const vertex = new Vector3();
		const normal = new Vector3();

		// generate vertices, normals and uvs

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

			for ( let i = 0; i <= tubularSegments; i ++ ) {

				const u = i / tubularSegments * arc;
				const v = j / radialSegments * Math.PI * 2;

				// vertex

				vertex.x = ( radius + tube * Math.cos( v ) ) * Math.cos( u );
				vertex.y = ( radius + tube * Math.cos( v ) ) * Math.sin( u );
				vertex.z = tube * Math.sin( v );

				vertices.push( vertex.x, vertex.y, vertex.z );

				// normal

				center.x = radius * Math.cos( u );
				center.y = radius * Math.sin( u );
				normal.subVectors( vertex, center ).normalize();

				normals.push( normal.x, normal.y, normal.z );

				// uv

				uvs.push( i / tubularSegments );
				uvs.push( j / radialSegments );

			}

		}

		// generate indices

		for ( let j = 1; j <= radialSegments; j ++ ) {

			for ( let i = 1; i <= tubularSegments; i ++ ) {

				// indices

				const a = ( tubularSegments + 1 ) * j + i - 1;
				const b = ( tubularSegments + 1 ) * ( j - 1 ) + i - 1;
				const c = ( tubularSegments + 1 ) * ( j - 1 ) + i;
				const d = ( tubularSegments + 1 ) * j + i;

				// faces

				indices.push( a, b, d );
				indices.push( b, c, d );

			}

		}

		// build geometry

		this.setIndex( indices );
		this.setAttribute( 'position', new Float32BufferAttribute( vertices, 3 ) );
		this.setAttribute( 'normal', new Float32BufferAttribute( normals, 3 ) );
		this.setAttribute( 'uv', new Float32BufferAttribute( uvs, 2 ) );

	}
Constructs a new torus geometry.

@param {number} [radius=1] - Radius of the torus, from the center of the torus to the center of the tube.
@param {number} [tube=0.4] - Radius of the tube. Must be smaller than `radius`.
@param {number} [radialSegments=12] - The number of radial segments.
@param {number} [tubularSegments=48] - The number of tubular segments.
@param {number} [arc=Math.PI*2] - Central angle in radians.