vertex displacement

pure javascript with intention of bulging cylinder

HTML

<div id="info">Bulged Cylinder
    <br/>Press Z to gain weight
    <br/>Press Y to lose weight
</div>
<script src="http://cdnjs.cloudflare.com/ajax/libs/three.js/r70/three.min.js"></script>
<script src="https://dl.dropboxusercontent.com/u/3587259/Code/Threejs/OrbitControls.js">
    
</script>
<script src="http://jyunming-chen.github.io/tutsplus/js/KeyboardState.js"></script>

CSS

#info {
    position: absolute;
    top: 0px;
    width: 100%;
    padding: 10px;
    text-align: center;
    color: #ffff00
}
body {
    overflow: hidden;
}

JavaScript

var camera, scene, renderer, geometry, material, mesh, controls;
var keyboard = new KeyboardState();
var height = 100;

init();
animate();

function init() {
    scene = new THREE.Scene();

    camera = new THREE.PerspectiveCamera(50, window.innerWidth / window.innerHeight, 1, 1000);
    camera.position.z = 500;
    scene.add(camera);

    geometry = new THREE.CylinderGeometry (50,50,height, 12, 20);
//  	geometry = new THREE.IcosahedronGeometry (height,2);
    
    material = new THREE.MeshBasicMaterial({wireframe:true});
    mesh = new THREE.Mesh(geometry, material);
    scene.add(mesh);
   
    renderer = new THREE.WebGLRenderer();
    renderer.setSize(window.innerWidth, window.innerHeight);
    renderer.setClearColor(0x888888);

    controls = new THREE.OrbitControls(camera, renderer.domElement);

    document.body.appendChild(renderer.domElement);
    window.addEventListener('resize', onWindowResize, false);
}

function onWindowResize() {
    camera.aspect = window.innerWidth / window.innerHeight;
    camera.updateProjectionMatrix();
    renderer.setSize(window.innerWidth, window.innerHeight);
}

function bulgeAmount (vertex) {
	var b;
    b = vertex.y > 0 ? height/2 : -height/2; 
    return Math.sin (Math.abs(vertex.y-b)/(height/2) * Math.PI/2);
}

function meshDeform(mode) {
    console.log ('deforming ...');
    var tmp = new THREE.Vector3();
    var scale;
	var va,vb,vc;
	var i;
        
    mesh.geometry.verticesNeedUpdate = true;
    for (i = 0; i < mesh.geometry.faces.length; i++) {
		// move three vertices of this face along its (vertex) normal direction, 
		var face = mesh.geometry.faces[ i ];
		var vertexNormals = face.vertexNormals;
        
        va = mesh.geometry.vertices[face.a];
		scale = bulgeAmount (va);        
        tmp.copy (vertexNormals[0]).normalize();
        tmp.multiplyScalar (mode*scale);
        va.add (tmp);

        vb = mesh.geometry.vertices[face.b];
		scale = bulgeAmount (vb);        
        tmp.copy...