text: // http://paulirish.com/2011/requestanimationframe-for-smart-animating/
  // http://my.opera.com/emoller/blog/2011/12/20/requestanimationframe-for-smart-er-animating
   
  // requestAnimationFrame polyfill by Erik Möller
  // fixes from Paul Irish and Tino Zijdel
   
  (function() {
      var lastTime = 0;
      var vendors = ['ms', 'moz', 'webkit', '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, element) {
              var currTime = Date.now();
              var timeToCall = Math.max(0, 16 - (currTime - lastTime));
              var id = window.setTimeout(function() { callback(currTime + timeToCall); },
                timeToCall);
              lastTime = currTime + timeToCall;
              return id;
          };
   
      if (!window.cancelAnimationFrame)
          window.cancelAnimationFrame = function(id) {
              clearTimeout(id);
          };
  }());