subtract shape

ViewController.swift

//
//  ViewController.swift
//  SubtractShape
//
//  Created by MizushimaYusuke on 1/7/16.
//  Copyright © 2016 MizushimaYusuke. All rights reserved.
//

import UIKit

class ViewController: UIViewController {
    
    var shapes = [CAShapeLayer]()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = UIColor.darkGrayColor()
        createShape()
        createButton()
    }
    
    func createShape() {
        let path = UIBezierPath()
        path.moveToPoint(CGPoint(x: -100, y: -120))
        path.addLineToPoint(CGPoint(x: 100, y: -120))
        path.addLineToPoint(CGPoint(x: 0, y: 150))
        path.closePath()
        
        let shape = CAShapeLayer()
        shape.path = path.CGPath
        shape.fillColor = UIColor.clearColor().CGColor
        shape.strokeColor = UIColor.orangeColor().CGColor
        shape.lineWidth = 5
        shape.position = CGPoint(x: CGRectGetMidX(view.bounds), y: 200)
        view.layer.addSublayer(shape)
        
        shapes.append(shape)
    }

    func createButton() {
        let btn = UIButton(type: .System)
        btn.setTitle("→", forState: .Normal)
        btn.titleLabel?.font = UIFont.boldSystemFontOfSize(50)
        btn.sizeToFit()
        btn.center = CGPoint(x: CGRectGetMidX(view.bounds), y: 400)
        view.addSubview(btn)
        btn.addTarget(self, action: "next", forControlEvents: .TouchUpInside)
    }
    
    func next() {
        if let shapecopy = shapes.last?.copy() as? CAShapeLayer {
            let path = UIBezierPath(CGPath: shapecopy.path!)
            path.applyTransform(CGAffineTransformMakeRotation(CGFloat(M_PI) / 12.0))
            shapecopy.path = path.CGPath
            view.layer.addSublayer(shapecopy)
            shapes.append(shapecopy)
            subtractShapes()
        }
    }
    
    func subtractShapes() {
        var mask : CAShapeLayer? = self.view.layer.sublayers?.filter { $0.name == "mask" }.first as? CAShapeLayer
        
        if mask == nil {
            mask = CAShapeLayer()
            mask!.name = "mask"
            mask!.lineWidth = 0
            mask!.position = CGPoint(x: CGRectGetMidX(view.bounds), y: 200)
            mask!.fillRule = kCAFillRuleEvenOdd
            mask!.fillColor = UIColor.orangeColor().CGColor
            view.layer.addSublayer(mask!)
        }
        
        let maskPath = UIBezierPath()
        maskPath.usesEvenOddFillRule = true
        
        for s in shapes {
            s.strokeColor = UIColor.clearColor().CGColor
            let stroke = CGPathCreateCopyByStrokingPath(s.path!, nil, 5, .Butt, .Miter, 0)
            maskPath.appendPath(UIBezierPath(CGPath: stroke!))
        }
        
        mask!.path = maskPath.CGPath
    }
}

extension CAShapeLayer {
    public override func copy() -> AnyObject {
        let copyLayer = CAShapeLayer()
        copyLayer.position = self.position
        copyLayer.fillColor = self.fillColor
        copyLayer.strokeColor = self.strokeColor
        copyLayer.lineWidth = self.lineWidth
        copyLayer.path = self.path!
        copyLayer.transform = self.transform
        return copyLayer
    }
}

http://lepetit-prince.net/ios/?p=4721