vdo.ninja/thirdparty/jeeliz/three/customMaterials/GlowMaterial/threex.dilategeometry.js

/**
 * @namespace
 */
var THREEx    = THREEx || {}

/**
 * dilate a geometry inplace
 * @param  {THREE.Geometry} geometry geometry to dilate
 * @param  {Number} length   percent to dilate, use negative value to erode
 */
THREEx.dilateGeometry    = function(geometry, length){
    // gather vertexNormals from geometry.faces
    var vertexNormals    = new Array(geometry.vertices.length);
    geometry.faces.forEach(function(face){
        if( face instanceof THREE.Face4 ){
            vertexNormals[face.a]    = face.vertexNormals[0];
            vertexNormals[face.b]    = face.vertexNormals[1];
            vertexNormals[face.c]    = face.vertexNormals[2];
            vertexNormals[face.d]    = face.vertexNormals[3];        
        }else if( face instanceof THREE.Face3 ){
            vertexNormals[face.a]    = face.vertexNormals[0];
            vertexNormals[face.b]    = face.vertexNormals[1];
            vertexNormals[face.c]    = face.vertexNormals[2];
        }else    console.assert(false);
    });
    // modify the vertices according to vertextNormal
    geometry.vertices.forEach(function(vertex, idx){
        var vertexNormal = vertexNormals[idx];
        vertex.x    += vertexNormal.x * length;
        vertex.y    += vertexNormal.y * length;
        vertex.z    += vertexNormal.z * length;
    });        
};