code: function _renderFrame(time) {
              var stage = _stages[_state].stage;
              // update all game objects
              me.game.update(time, stage);
              // render all game objects
              me.game.draw(stage);
              // schedule the next frame update
              if (_animFrameId !== -1) {
                  _animFrameId = window.requestAnimationFrame(_renderFrame);
              }
          }
docs: this is only called when using requestAnimFrame stuff
  @param {Number} time current timestamp in milliseconds
  @ignore