Vector.js

/**
 * @author mr.doob / http://mrdoob.com/
 * @author philogb / http://blog.thejit.org/
 * @author egraether / http://egraether.com/
 * @author zz85 / http://www.lab4games.net/zz85/blog
 * @author jonobr1 / http://jonobr1.com/
 */

define([
  'common'
], function(_) {

  /**
   * A two dimensional vector.
   */
  var Vector = function(x, y) {

    this.x = x || 0;
    this.y = y || 0;

  };

  _.extend(Vector.prototype, {

    set: function(x, y) {
      this.x = x;
      this.y = y;
      return this;
    },

    copy: function(v) {
      this.x = v.x;
      this.y = v.y;
      return this;
    },

    clear: function() {
      this.x = 0;
      this.y = 0;
      return this;
    },

    clone: function() {
      return new Vector(this.x, this.y);
    },

    add: function(v1, v2) {
      this.x = v1.x + v2.x;
      this.y = v1.y + v2.y;
      return this;
    },

    addSelf: function(v) {
      this.x += v.x;
      this.y += v.y;
      return this;
    },

    sub: function(v1, v2) {
      this.x = v1.x - v2.x;
      this.y = v1.y - v2.y;
      return this;
    },

    subSelf: function(v) {
      this.x -= v.x;
      this.y -= v.y;
      return this;
    },

    multiplySelf: function(v) {
      this.x *= v.x;
      this.y *= v.y;
      return this;
    },

    multiplyScalar: function(s) {
      this.x *= s;
      this.y *= s;
      return this;
    },

    divideScalar: function(s) {
      if (s) {
        this.x /= s;
        this.y /= s;
      } else {
        this.set(0, 0);
      }
      return this;
    },

    negate: function() {
      return this.multiplyScalar(-1);
    },

    dot: function(v) {
      return this.x * v.x + this.y * v.y;
    },

    lengthSquared: function() {
      return this.x * this.x + this.y * this.y;
    },

    length: function() {
      return Math.sqrt(this.lengthSquared());
    },

    normalize: function() {
      return this.divideScalar(this.length());
    },

    distanceTo: function(v) {
      return Math.sqrt(this.distanceToSquared(v));
    },

    distanceToSquared: function(v) {
      var dx = this.x - v.x, dy = this.y - v.y;
      return dx * dx + dy * dy;
    },

    setLength: function(l) {
      return this.normalize().multiplyScalar(l);
    },

    equals: function(v) {
      return (this.distanceTo(v) < 0.0001 /* almost same position */);
    },

    lerp: function(v, t) {
      var x = (v.x - this.x) * t + this.x;
      var y = (v.y - this.y) * t + this.y;
      return this.set(x, y);
    },

    isZero: function() {
      return (this.length() < 0.0001 /* almost zero */ );
    }

  });

  return Vector;

});