CAlayer to UIImage bug with shadow

Question

i'm trying to render UIImage from CALayer keeping shadows, but the resulting image is different from the image in CALayer, why?

code

override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        self.view.backgroundColor = UIColor.black
        
        
        let containerLayer = CALayer()
        containerLayer.frame = CGRect(x: 100, y: 20, width: 40, height: 200)
        
        let layerGradient = CAGradientLayer()
        layerGradient.frame = CGRect(x: 15, y: 0, width: 10, height: 200)
        layerGradient.startPoint = CGPoint(x: 0, y: 0.5)
        layerGradient.endPoint = CGPoint(x: 1, y: 0.5)
        layerGradient.colors = [UIColor.black.cgColor, UIColor.white.cgColor, UIColor.black.cgColor]
        layerGradient.shadowOffset = CGSize(width: -3, height: 0)
        layerGradient.shadowPath = UIBezierPath(rect: CGRect(x: 0, y: 0, width: 15, height: 200)).cgPath
        layerGradient.shadowRadius = 7
        layerGradient.shadowColor = UIColor.black.cgColor
        layerGradient.shadowOpacity = 1
        
        containerLayer.backgroundColor = UIColor.white.cgColor
        
        containerLayer.addSublayer(layerGradient)
        self.view.layer.addSublayer(containerLayer)
        
        
        let imageSeparator = imageFromLayer(layer: containerLayer)
               
        let img = UIImageView(image: imageSeparator)
        self.view.addSubview(img)
        
    }

    func imageFromLayer(layer:CALayer) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(layer.frame.size, layer.isOpaque, layer.contentsScale)
        layer.render(in: UIGraphicsGetCurrentContext()!)
        let outputImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return outputImage!
    }

CALayer

Result UIImage

where am i wrong?

Answer 1

after searching and testing, it turned out that the problem is in the shadowPath, and you can render it only through UIView and drawhierarchy https://developer.apple.com/documentation/uikit/uiview/1622589-drawhierarchy

extension UIImage{
    convenience init(view: UIView) {

    UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.isOpaque, 0.0)
    view.drawHierarchy(in: view.bounds, afterScreenUpdates: true)
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    self.init(cgImage: (image?.cgImage)!)

  }
}