Swift CAShapeLayer: 创建圆形遮罩

let layer = CAShapeLayer() let pathRef = CGMutablePath() let frame = circleView.frame CGPathAddRelativeArc(pathRef, nil, frame.size.width/2.0, frame.size.height/2.0, frame.size.width < frame.size.height ? frame.size.width/2.0-5 : frame.size.height/2.0-5, 0, 2*CGFloat.pi) layer.path = pathRef layer.lineWidth = 5 layer.fillColor = UIColor.clear.cgColor layer.strokeColor = UIColor.black.cgColor CGPathRelease(pathRef) circleView.layer.mask = layer