THREE.js Flat Triangle Subdivide

FlatSubdivide.js

// Triangle Subdivision based on http://wiki.unity3d.com/index.php?title=MeshHelper
// There is not smoothing of any sort, it will just divide the triangles
// hence the FlatSubdivide name

THREE.FlatSubdivide = function () {

};

// Applies the "modify" pattern
THREE.FlatSubdivide.prototype.modify = function ( geometry ) {
	
	this.subdiv( geometry );
	
	geometry.computeFaceNormals();
	geometry.computeVertexNormals();

};

( function() {

	THREE.FlatSubdivide.prototype.subdiv = function ( geometry ) {
		
		var map = []

		var newFaces = []
		var vertices = geometry.vertices

		var faces = geometry.faces
		var numFaces = faces.length

		for(var i=0; i < numFaces; ++i) {
			var i1 = faces[i].a
			var i2 = faces[i].b
			var i3 = faces[i].c

			var a = getNewVertex(i1,i2,map, vertices)
			var b = getNewVertex(i2,i3,map, vertices) 
			var c = getNewVertex(i3,i1,map, vertices)

			newFaces.push(new THREE.Face3(i1,a,c))
			newFaces.push(new THREE.Face3(i2,b,a))
			newFaces.push(new THREE.Face3(i3,c,b))
			newFaces.push(new THREE.Face3(a,b,c))
		}

		geometry.faces = newFaces

	};

	function getEdgeKey(i1, i2) {
		
		var vertexIndexA = Math.min( i1, i2 );
		var vertexIndexB = Math.max( i1, i2 );

		return vertexIndexA + "_" + vertexIndexB;
	}

	function GetMiddle(pointA, pointB) {
		var middle = new THREE.Vector3()
		middle.subVectors(pointB.clone() , pointA.clone())
		middle.multiplyScalar( 0.5)
		middle.subVectors(pointB.clone(), middle )
		return middle.clone()
	}

	function getNewVertex(i1, i2, map, vertices) {
		var newIndex = vertices.length

		var edgeKey = getEdgeKey(i1, i2)

		if(edgeKey in map ) {
			return map[edgeKey];
		}
		
		// add new index
		map[edgeKey] = newIndex

		// get the middle of the edge
		var middle = GetMiddle(vertices[i1], vertices[i2])

		vertices.push(middle)

		return newIndex
	}

} )();