// make sure requestAnimationFrame and cancelAnimationFrame are defined
// polyfill for browsers without native support
// by Opera engineer Erik Möller
(function () {
  var lastTime = 0;
  var vendors = ['webkit', 'moz', 'ms', 'o'];
  for (var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
    window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
    window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] ||
      window[vendors[x] + 'CancelRequestAnimationFrame'];
  }
  if (!window.requestAnimationFrame) {
    window.requestAnimationFrame = function (callback) {
      var currTime = new Date().getTime();
      var timeToCall = Math.max(0, 16 - (currTime - lastTime));
      var id = window.setTimeout(function () { return callback(currTime + timeToCall); }, timeToCall);
      lastTime = currTime + timeToCall;
      return id;
    };
  }
  if (!window.cancelAnimationFrame) {
    window.cancelAnimationFrame = function (id) {
      clearTimeout(id);
    };
  }
})();