// adds requestAnimationFrame functionality
// Source: http://strd6.com/2011/05/better-window-requestanimationframe-shim/

window.requestAnimationFrame || (window.requestAnimationFrame = 
  window.webkitRequestAnimationFrame || 
  window.mozRequestAnimationFrame    || 
  window.oRequestAnimationFrame      || 
  window.msRequestAnimationFrame     || 
  function(callback, element) {
    return window.setTimeout(function() {
      callback(+new Date());
  }, 1000 / 60);
});
