Exploring ParametricGeometry2

ParametricGeometry2.js

/**
 * @author zz85 / https://github.com/zz85
 * Parametric Surfaces Geometry
 * based on the brilliant article by @prideout http://prideout.net/blog/?p=44
 *
 * new THREE.ParametricGeometry( parametricFunction, uSegments, ySegements );
 *
 */

THREE.ParametricGeometry2 = function ( func, slices, stacks ) {

	THREE.Geometry2.call( this, slices * stacks * 2 * 3 );

	// Buffer needed is slices * stacks * 2 triangles * 3 vertices

	var vertices = this.vertices;
	var normals = this.normals;
	var uvs = this.uvs;

	var i, il, j, p;
	var u, v;

	var offset = 0;

	var stackCount = stacks + 1;
	var sliceCount = slices + 1;

	var verts = [];

	for ( i = 0; i <= stacks; i ++ ) {

		v = i / stacks;

		for ( j = 0; j <= slices; j ++ ) {

			u = j / slices;

			p = func( u, v );
			verts.push( p );

		}
	}

	var a, b, c, d;
	var uva, uvb, uvc, uvd;
	var uvOffset = 0;

	function verts_push() {
		for (var i=0; i < arguments.length; i++) {
			vertices[ offset++ ] = arguments[i];
		}
	}

	function uvs_push() {
		for (var i=0; i < arguments.length; i++) {
			uvs[ uvOffset++ ] = arguments[i];
		}
	}

	uva = new THREE.Vector2();
	uvb = new THREE.Vector2();
	uvc = new THREE.Vector2();
	uvd = new THREE.Vector2();

	for ( i = 0; i < stacks; i ++ ) {

		for ( j = 0; j < slices; j ++ ) {

			a = i * sliceCount + j;
			b = i * sliceCount + j + 1;
			c = (i + 1) * sliceCount + j + 1;
			d = (i + 1) * sliceCount + j;

			var va = verts[ a ],
				vb = verts[ b ],
				vc = verts[ c ],
				vd = verts[ d ];

			verts_push( va.x, va.y, va.z,
						vb.x, vb.y, vb.z,
						vd.x, vd.y, vd.z );

			verts_push( vb.x, vb.y, vb.z,
						vc.x, vc.y, vc.z,
						vd.x, vd.y, vd.z );

			// Equivalent of
			// faces.push( new THREE.Face3( a, b, d ) );
			// faces.push( new THREE.Face3( b, c, d ) );

			uva.set( j / slices, i / stacks );
			uvb.set( (j + 1 ) / slices, i / stacks );
			uvc.set( ( j + 1 ) / slices, ( i + 1 ) / stacks );
			uvd.set( j / slices, ( i + 1 ) / stacks );

			uvs_push( uva.x, uva.y, uvb.x, uvb.y, uvd.x, uvd.y );
			uvs_push( uvb.x, uvb.y, uvc.x, uvc.y, uvd.x, uvd.y );

			// uvs.push( [ uva, uvb, uvd ] );
			// uvs.push( [ uvb.clone(), uvc, uvd.clone() ] );

		}

	}



	var normal = new THREE.Vector3();

	var cb = new THREE.Vector3(), ab = new THREE.Vector3();
	var vA = new THREE.Vector3(), vB = new THREE.Vector3(), vC = new THREE.Vector3();

	/* Yeah compute all face normals given all vertices are triangles */
	function computeFaceNormals() {

		var l = vertices.length / 3 / 3;
		var j;
		var m = 0;

		for (var i = 0; i < l; i++ ) {
			j = i * 3 * 3;

			vA.set( vertices[ j++ ], vertices[ j++ ], vertices[ j++ ] );
			vB.set( vertices[ j++ ], vertices[ j++ ], vertices[ j++ ] );
			vC.set( vertices[ j++ ], vertices[ j++ ], vertices[ j++ ] );
			
			cb.subVectors( vC, vB );
			ab.subVectors( vA, vB );
			cb.cross( ab ).normalize();

			normal.copy( cb );

			normals[ m++ ] = normal.x;
			normals[ m++ ] = normal.y;
			normals[ m++ ] = normal.z;

		}

	}

	// this.computeCentroids();
	computeFaceNormals();
	// this.computeVertexNormals();


};

THREE.ParametricGeometry2.prototype = Object.create( THREE.Geometry2.prototype );