three.js/src/extras/geometries/RingGeometry.js

/**
 * @author Kaleb Murphy
 */

THREE.RingGeometry = function ( innerRadius, outerRadius, thetaSegments, phiSegments, thetaStart, thetaLength ) {

	THREE.Geometry.call( this );

	this.type = 'RingGeometry';

	this.parameters = {
		innerRadius: innerRadius,
		outerRadius: outerRadius,
		thetaSegments: thetaSegments,
		phiSegments: phiSegments,
		thetaStart: thetaStart,
		thetaLength: thetaLength
	};

	innerRadius = innerRadius || 0;
	outerRadius = outerRadius || 50;

	thetaStart = thetaStart !== undefined ? thetaStart : 0;
	thetaLength = thetaLength !== undefined ? thetaLength : Math.PI * 2;

	thetaSegments = thetaSegments !== undefined ? Math.max( 3, thetaSegments ) : 8;
	phiSegments = phiSegments !== undefined ? Math.max( 1, phiSegments ) : 8;

	var i, o, uvs = [], radius = innerRadius, radiusStep = ( ( outerRadius - innerRadius ) / phiSegments );

	for ( i = 0; i < phiSegments + 1; i ++ ) { // concentric circles inside ring

		for ( o = 0; o < thetaSegments + 1; o ++ ) { // number of segments per circle

			var vertex = new THREE.Vector3();
			var segment = thetaStart + o / thetaSegments * thetaLength;
			vertex.x = radius * Math.cos( segment );
			vertex.y = radius * Math.sin( segment );

			this.vertices.push( vertex );
			uvs.push( new THREE.Vector2( ( vertex.x / outerRadius + 1 ) / 2, ( vertex.y / outerRadius + 1 ) / 2 ) );
		}

		radius += radiusStep;

	}

	var n = new THREE.Vector3( 0, 0, 1 );

	for ( i = 0; i < phiSegments; i ++ ) { // concentric circles inside ring

		var thetaSegment = i * (thetaSegments + 1);

		for ( o = 0; o < thetaSegments ; o ++ ) { // number of segments per circle

			var segment = o + thetaSegment;

			var v1 = segment;
			var v2 = segment + thetaSegments + 1;
			var v3 = segment + thetaSegments + 2;

			this.faces.push( new THREE.Face3( v1, v2, v3, [ n.clone(), n.clone(), n.clone() ] ) );
			this.faceVertexUvs[ 0 ].push( [ uvs[ v1 ].clone(), uvs[ v2 ].clone(), uvs[ v3 ].clone() ]);

			v1 = segment;
			v2 = segment + thetaSegments + 2;
			v3 = segment + 1;

			this.faces.push( new THREE.Face3( v1, v2, v3, [ n.clone(), n.clone(), n.clone() ] ) );
			this.faceVertexUvs[ 0 ].push( [ uvs[ v1 ].clone(), uvs[ v2 ].clone(), uvs[ v3 ].clone() ]);

		}
	}

	this.computeFaceNormals();

	this.boundingSphere = new THREE.Sphere( new THREE.Vector3(), radius );

};

THREE.RingGeometry.prototype = Object.create( THREE.Geometry.prototype );
THREE.RingGeometry.prototype.constructor = THREE.RingGeometry;