Octahedron.js

var geom = require('pex-geom');
var Vec3 = geom.Vec3;
var Geometry = geom.Geometry;

function Octahedron(r) {
  r = r || 0.5;

  var a = 1 / (2 * Math.sqrt(2));
  var b = 1 / 2;

  var s3 = Math.sqrt(3);
  var s6 = Math.sqrt(6);

  var vertices = [
    new Vec3(-a, 0, a), //front left
    new Vec3( a, 0, a), //front right
    new Vec3( a, 0,-a), //back right
    new Vec3(-a, 0,-a), //back left
    new Vec3( 0, b, 0), //top
    new Vec3( 0,-b, 0)  //bottom
  ];

  vertices = vertices.map(function(v) { return v.normalize().scale(r); })

  var faces = [
    [3, 0, 4],
    [2, 3, 4],
    [1, 2, 4],
    [0, 1, 4],
    [3, 2, 5],
    [0, 3, 5],
    [2, 1, 5],
    [1, 0, 5]
  ];

  var edges = [
    [0, 1],
    [1, 2],
    [2, 3],
    [3, 0],
    [0, 4],
    [1, 4],
    [2, 4],
    [3, 4],
    [0, 5],
    [1, 5],
    [2, 5],
    [3, 5]
  ];

  Geometry.call(this, { vertices: vertices, faces: faces, edges: edges });
}

Octahedron.prototype = Object.create(Geometry.prototype);

module.exports = Octahedron;