constructor( radiusTop = 1, radiusBottom = 1, height = 1, radialSegments = 32, heightSegments = 1, openEnded = false, thetaStart = 0, thetaLength = Math.PI * 2 ) {

		super();

		this.type = 'CylinderGeometry';

		/**
		 * 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 = {
			radiusTop: radiusTop,
			radiusBottom: radiusBottom,
			height: height,
			radialSegments: radialSegments,
			heightSegments: heightSegments,
			openEnded: openEnded,
			thetaStart: thetaStart,
			thetaLength: thetaLength
		};

		const scope = this;

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

		// buffers

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

		// helper variables

		let index = 0;
		const indexArray = [];
		const halfHeight = height / 2;
		let groupStart = 0;

		// generate geometry

		generateTorso();

		if ( openEnded === false ) {

			if ( radiusTop > 0 ) generateCap( true );
			if ( radiusBottom > 0 ) generateCap( false );

		}

		// 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 ) );

		function generateTorso() {

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

			let groupCount = 0;

			// this will be used to calculate the normal
			const slope = ( radiusBottom - radiusTop ) / height;

			// generate vertices, normals and uvs

			for ( let y = 0; y <= heightSegments; y ++ ) {

				const indexRow = [];

				const v = y / heightSegments;

				// calculate the radius of the current row

				const radius = v * ( radiusBottom - radiusTop ) + radiusTop;

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

					const u = x / radialSegments;

					const theta = u * thetaLength + thetaStart;

					const sinTheta = Math.sin( theta );
					const cosTheta = Math.cos( theta );

					// vertex

					vertex.x = radius * sinTheta;
					vertex.y = - v * height + halfHeight;
					vertex.z = radius * cosTheta;
					vertices.push( vertex.x, vertex.y, vertex.z );

					// normal

					normal.set( sinTheta, slope, cosTheta ).normalize();
					normals.push( normal.x, normal.y, normal.z );

					// uv

					uvs.push( u, 1 - v );

					// save index of vertex in respective row

					indexRow.push( index ++ );

				}

				// now save vertices of the row in our index array

				indexArray.push( indexRow );

			}

			// generate indices

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

				for ( let y = 0; y < heightSegments; y ++ ) {

					// we use the index array to access the correct indices

					const a = indexArray[ y ][ x ];
					const b = indexArray[ y + 1 ][ x ];
					const c = indexArray[ y + 1 ][ x + 1 ];
					const d = indexArray[ y ][ x + 1 ];

					// faces

					if ( radiusTop > 0 || y !== 0 ) {

						indices.push( a, b, d );
						groupCount += 3;

					}

					if ( radiusBottom > 0 || y !== heightSegments - 1 ) {

						indices.push( b, c, d );
						groupCount += 3;

					}

				}

			}

			// add a group to the geometry. this will ensure multi material support

			scope.addGroup( groupStart, groupCount, 0 );

			// calculate new start value for groups

			groupStart += groupCount;

		}

		function generateCap( top ) {

			// save the index of the first center vertex
			const centerIndexStart = index;

			const uv = new Vector2();
			const vertex = new Vector3();

			let groupCount = 0;

			const radius = ( top === true ) ? radiusTop : radiusBottom;
			const sign = ( top === true ) ? 1 : -1;

			// first we generate the center vertex data of the cap.
			// because the geometry needs one set of uvs per face,
			// we must generate a center vertex per face/segment

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

				// vertex

				vertices.push( 0, halfHeight * sign, 0 );

				// normal

				normals.push( 0, sign, 0 );

				// uv

				uvs.push( 0.5, 0.5 );

				// increase index

				index ++;

			}

			// save the index of the last center vertex
			const centerIndexEnd = index;

			// now we generate the surrounding vertices, normals and uvs

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

				const u = x / radialSegments;
				const theta = u * thetaLength + thetaStart;

				const cosTheta = Math.cos( theta );
				const sinTheta = Math.sin( theta );

				// vertex

				vertex.x = radius * sinTheta;
				vertex.y = halfHeight * sign;
				vertex.z = radius * cosTheta;
				vertices.push( vertex.x, vertex.y, vertex.z );

				// normal

				normals.push( 0, sign, 0 );

				// uv

				uv.x = ( cosTheta * 0.5 ) + 0.5;
				uv.y = ( sinTheta * 0.5 * sign ) + 0.5;
				uvs.push( uv.x, uv.y );

				// increase index

				index ++;

			}

			// generate indices

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

				const c = centerIndexStart + x;
				const i = centerIndexEnd + x;

				if ( top === true ) {

					// face top

					indices.push( i, i + 1, c );

				} else {

					// face bottom

					indices.push( i + 1, i, c );

				}

				groupCount += 3;

			}

			// add a group to the geometry. this will ensure multi material support

			scope.addGroup( groupStart, groupCount, top === true ? 1 : 2 );

			// calculate new start value for groups

			groupStart += groupCount;

		}

	}
Constructs a new cylinder geometry.

@param {number} [radiusTop=1] - Radius of the cylinder at the top.
@param {number} [radiusBottom=1] - Radius of the cylinder at the bottom.
@param {number} [height=1] - Height of the cylinder.
@param {number} [radialSegments=32] - Number of segmented faces around the circumference of the cylinder.
@param {number} [heightSegments=1] - Number of rows of faces along the height of the cylinder.
@param {boolean} [openEnded=false] - Whether the base of the cylinder is open or capped.
@param {number} [thetaStart=0] - Start angle for first segment, in radians.
@param {number} [thetaLength=Math.PI*2] - The central angle, often called theta, of the circular sector, in radians.
The default value results in a complete cylinder.