let gradientLayer = CAGradientLayer()
gradientLayer.frame = self.view.frame
gradientLayer.colors = [UIColor.red.cgColor,UIColor.yellow.cgColor]
gradientLayer.startPoint = CGPoint(x: 0,y: 0)
gradientLayer.endPoint = CGPoint(x: 1, y: 1)
self.view.layer.addSublayer(gradientLayer)
let biz = UIBezierPath(arcCenter: self.view.center, radius: 100, startAngle: 0, endAngle: Double.pi * 2, clockwise: true)
let shapeLayer = CAShapeLayer()
shapeLayer.path = biz.cgPath
shapeLayer.lineWidth = 30.0
shapeLayer.fillColor = UIColor.clear.cgColor
shapeLayer.strokeColor = UIColor.white.cgColor
self.view.layer.addSublayer(shapeLayer)
self.view.layer.mask = shapeLayer
