class ViewController: UIViewController {
	
	var img1: UIImage!
	
	override func viewDidLoad() {
		super.viewDidLoad()
		
		guard let i1 = UIImage(named: "p3x3"),
			  let i2 = UIImage(named: "p2x2"),
			  let i3 = UIImage(named: "p1x1")
		else {
			fatalError("failed to load images")
		}
		
		i1.mergeWithTopmage(topImage: i2, completion: { img in
			img.mergeWithTopmage(topImage: i3, completion: { img in
				self.img1 = img
			})
		})
	}
	
	override func viewDidAppear(_ animated: Bool) {
		super.viewDidAppear(animated)
		
		let imgView = UIImageView(image: img1)
		view.addSubview(imgView)
		imgView.center = view.center
		
	}
	
}