missing circle

ViewController.swift

//
//  ViewController.swift
//  MissingCircle
//
//  Created by MizushimaYusuke on 2017/10/12.
//  Copyright © 2017 MizushimaYusuke. All rights reserved.
//

import UIKit
import SpriteKit

class ViewController: UIViewController {

    weak var scene: SKScene?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupScene()
        createWall()
    }

    func setupScene() {
        let sv = SKView(frame: view.bounds)
        sv.showsPhysics = true
        let s = SKScene(size: sv.frame.size)
        sv.presentScene(s)
        view.addSubview(sv)
        scene = s
    }
    
    func createWall() {
        let wall = SKSpriteNode(color: .clear, size: view.frame.size)
        wall.position = view.center
        scene?.addChild(wall)
        wall.physicsBody = SKPhysicsBody(edgeLoopFrom: CGRect(origin: CGPoint(x: -view.center.x, y: -view.center.y), size: wall.frame.size))
        wall.physicsBody?.isDynamic = false
    }

    func createMissingCircle() -> SKNode {
        let hue = CGFloat(arc4random_uniform(10)) * 0.1
        let color = UIColor(hue: hue, saturation: 0.7, brightness: 1, alpha: 1)
        let s = CGFloat(arc4random_uniform(30)) + 30
        UIGraphicsBeginImageContextWithOptions(CGSize(width: s, height: s), false, 0)
        if let ctx = UIGraphicsGetCurrentContext() {
            color.set()
            ctx.fillEllipse(in: CGRect(x: 0, y: 0, width: s, height: s))
            ctx.setBlendMode(.clear)
            ctx.fillEllipse(in: CGRect(x: s * 0.2, y: s * 0.8, width: s, height: s))
        }
        let img = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        
        let texture = SKTexture(image: img)
        let n = SKSpriteNode(texture: texture)
        n.physicsBody = SKPhysicsBody(texture: texture, size: texture.size())
        self.scene?.addChild(n)
        return n
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first {
            let p = touch.location(in: scene!)
            let n = createMissingCircle()
            n.position = p
        }
    }
}

http://lepetit-prince.net/ios/?p=6739