带有阴影的 CAlayer 到 UIImage 错误答案

【问题标题】：CAlayer to UIImage bug with shadow带有阴影的 CAlayer 到 UIImage 错误
【发布时间】：2020-12-15 07:13:46
【问题描述】：

我正在尝试从 CALayer 渲染 UIImage 保持阴影，但生成的图像与 CALayer 中的图像不同，为什么？

代码

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

结果 UIImage

我哪里错了？

【问题讨论】：

标签： ios swift uiimage calayer shadow

【解决方案1】：

搜索测试后发现问题出在shadowPath上，只能通过UIView和drawhierarchy渲染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)!)

  }
}

【讨论】：