BlurMask

import UIKit
import PlaygroundSupport

extension UIView
{
    var snapshot: UIImage?
    {
        UIGraphicsBeginImageContextWithOptions(self.bounds.size, false, 0)
        self.drawHierarchy(in: self.bounds, afterScreenUpdates: true)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}

let brushWidth: CGFloat = 100

let imageView = UIImageView(image: UIImage(named: "image.jpg"))

let blurEffect = UIBlurEffect(style: .dark)

let effectView = UIVisualEffectView(effect: blurEffect)
effectView.frame = imageView.bounds

let view = UIView(frame: imageView.bounds)

view.addSubview(imageView)
view.addSubview(effectView)

let shapeLayer = CAShapeLayer()

func drawLine(from fromPoint: CGPoint, to toPoint: CGPoint)
{
    let path: UIBezierPath
    if let layerPath = shapeLayer.path
    {
        path = UIBezierPath(cgPath: layerPath)
    }
    else
    {
        path = UIBezierPath()
    }
    path.move(to: fromPoint)
    path.addLine(to: toPoint)
    shapeLayer.path = path.cgPath
    shapeLayer.lineWidth = brushWidth
    shapeLayer.lineCap = "round"
    shapeLayer.strokeColor = UIColor.black.cgColor
}



let image = view.snapshot!


effectView.removeFromSuperview()
let topImageView = UIImageView(image: image)
view.addSubview(topImageView)

topImageView.layer.mask = shapeLayer
drawLine(from: CGPoint(x: 0, y: 0), to: CGPoint(x: imageView.frame.maxX, y: imageView.frame.maxY))
drawLine(from: CGPoint(x: 0, y: imageView.frame.maxY), to: CGPoint(x: imageView.frame.maxX, y: 0))


PlaygroundPage.current.liveView = view