var fps = 0, now, lastUpdate = (new Date())*1 - 1;
  var fpsFilter = 50;


  var step = function() {
    requestAnimationFrame(step);

    var thisFrameFPS = 1000 / ((now=new Date()) - lastUpdate);
    if (now!=lastUpdate){
      fps += (thisFrameFPS - fps) / fpsFilter;
      lastUpdate = now * 1 - 1;
    }
  }