Swift - 从一个SKScene转换到UIViewController并返回的FPS减少

Question

当我从GameScene（SKScene）转移到Market（UIViewController）并返回时，FPS会降低。你能说出为什么？ ，问题在哪里？ MarketView是空的，没有证据，只有通过协议（SKScne）执行的转换，它绑定了GameScene和GameViewController。代码：

//GameScene

import SpriteKit
protocol GameDelegate {
func Market()
func Question()
}
...
func returnToMarket(){
self.viewController.Market()
}
// GameViewController

class GameViewController: UIViewController , GameDelegate{
func Market() {
    let storyBoard : UIStoryboard = UIStoryboard(name: "Market", bundle: nil)
    let vc : UIViewController =         storyBoard.instantiateViewControllerWithIdentifier("Market") 
    self.presentViewController(vc, animated: true, completion: nil)
}
...


}

// Market(UIViewController)
func ReturnToMainMeny() {
    let storyBoard : UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
    let vc : UIViewController = storyBoard.instantiateViewControllerWithIdentifier("GameViewController")
   self.presentViewController(vc, animated: true, completion: nil)

}