使用CAGradientLayer作为背景,同时使用drawRect绘制上下文:

# 使用CAGradientLayer作为背景
background_layer = CAGradientLayer()
background_layer.frame = self.view.bounds
background_layer.colors = [UIColor.clear.cgColor, UIColor.blue.cgColor]
self.view.layer.addSublayer(background_layer)

# 使用drawRect绘制上下文
context = UIGraphicsGetCurrentContext()
context?.setFillColorSpace(CGColorSpace.init(name: CGColorSpace.displayP3)!)
context?.fill(CGRect(x: 0, y: 0, width: 200, height: 200))
context?.setStrokeColorSpace(CGColorSpace.init(name: CGColorSpace.displayP3)!)
context?.setLineCap(CGLineCap.round)
context?.setLineJoin(CGLineJoin.round)
context?.setLineWidth(1.0)
context?.setStrokeColor(UIColor.black.cgColor)
context?.stroke(CGRect(x: 0, y: 0, width: 200, height: 200))