Hello SpriteKit

HelloSpriteKit.swift

import SpriteKit
import PlaygroundSupport

class Square: SKShapeNode {
    convenience init(position: CGPoint = .zero, oneSide: CGFloat = 0.0, strokeColor: SKColor = .white) {
        let c = CGFloat(oneSide * 0.2)
        let r = CGSize(width: oneSide, height: oneSide)
        self.init(rectOf: r, cornerRadius: c)
        self.position = position
        self.strokeColor = strokeColor
        let spin = SKAction.repeatForever(
            .rotate(byAngle: CGFloat(M_PI), duration: 1.0)
        )
        let remove = SKAction.sequence([
            .wait(forDuration: 0.5),
            .fadeOut(withDuration: 0.5),
            .removeFromParent()
            ])
        self.run(spin)
        self.run(remove)
    }
}

class Scene: SKScene, SKPhysicsContactDelegate {
    
    let label = SKLabelNode(text: "hello world")
    
    private func addSquare(positionBy touches: Set<UITouch>, color: SKColor) {
        for t in touches {
            let l = t.location(in: self)
            let n = Square(position: l, oneSide: 100.0, strokeColor: color)
            addChild(n)
        }
    }
    
    override func didMove(to view: SKView) {
        scaleMode = .resizeFill
        addChild(label)
    }
    
    override func didChangeSize(_ oldSize: CGSize) {
        label.position = CGPoint(x: size.width / 2, y: size.height / 2)
    }
    
    var lastTime = TimeInterval()
    
    override func update(_ currentTime: TimeInterval) {
        if lastTime + 1.5 > currentTime {
            return
        }
        lastTime = currentTime
        label.alpha = 1.0
        label.run(.fadeOut(withDuration: 1.0))
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        addSquare(positionBy: touches, color: .green)
    }
    
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        addSquare(positionBy: touches, color: .blue)
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        addSquare(positionBy: touches, color: .red)
    }
    
    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
        addSquare(positionBy: touches, color: .red)
    }
    
    func didBegin(_ contact: SKPhysicsContact) {
        // Called when two bodies first contact each other.
    }
    
    func didEnd(_ contact: SKPhysicsContact) {
        // Called when the contact ends between two physics bodies.
    }
    
}

let view = SKView()
view.showsDrawCount = true
view.showsNodeCount = true
view.showsFPS = true
view.presentScene(Scene())
PlaygroundPage.current.liveView = view