Canvas.js

(function() {
  /**
   * Canvas utility.
   * @static
   * @constructor
   */
  tracking.Canvas = {};

  /**
   * Loads an image source into the canvas.
   * @param {HTMLCanvasElement} canvas The canvas dom element.
   * @param {string} src The image source.
   * @param {number} x The canvas horizontal coordinate to load the image.
   * @param {number} y The canvas vertical coordinate to load the image.
   * @param {number} width The image width.
   * @param {number} height The image height.
   * @param {function} opt_callback Callback that fires when the image is loaded
   *     into the canvas.
   * @static
   */
  tracking.Canvas.loadImage = function(canvas, src, x, y, width, height, opt_callback) {
    var instance = this;
    var img = new window.Image();
    img.crossOrigin = '*';
    img.onload = function() {
      var context = canvas.getContext('2d');
      canvas.width = width;
      canvas.height = height;
      context.drawImage(img, x, y, width, height);
      if (opt_callback) {
        opt_callback.call(instance);
      }
      img = null;
    };
    img.src = src;
  };
}());