Swift 带角和隐藏底部边框的按钮

我想要的结果

我得到的是：

我使用以下代码：

    func roundedTopLeftButton(radius : Int, colorBorder : UIColor) {
    // Add border
       let gradient = CAGradientLayer()
       let size = CGSize(width: self.frame.width, height: self.frame.height)
       let rect = CGRect(origin: .zero, size: size)
       gradient.frame =  CGRect(origin: CGPoint.zero, size: size)
       gradient.colors = [UIColor.blue.cgColor, UIColor.green.cgColor]


       let shape = CAShapeLayer()
       shape.lineWidth = 2


       shape.path = UIBezierPath(roundedRect: rect,
       byRoundingCorners: [.topLeft , .topRight],
       cornerRadii: CGSize(width: radius, height: radius)).cgPath
       shape.strokeColor = colorBorder.cgColor
       shape.fillColor = UIColor.clear.cgColor
       gradient.mask = shape

    self.layer.addSublayer(shape)
}

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请如何隐藏按钮组的按钮边框？

使用自定义路径，没有复杂的角半径。 你只需要在纸上画出你的形状。标出兴趣点，了解一点三角学（这只是了解角度）和一点基本几何

let path = UIBezierPath()
path.move(to: CGPoint(x: 0, y: bounds.size.height))
path.addLine(to: CGPoint(x: 0, y: radius))
path.addArc(withCenter: CGPoint(x: radius, y: radius),
            radius: radius,
            startAngle: CGFloat.pi,
            endAngle: -CGFloat.pi/2.0,
            clockwise: true)
path.addLine(to: CGPoint(x: bounds.size.width - radius, y: 0))
path.addArc(withCenter: CGPoint(x: bounds.width - radius, y: radius),
            radius: radius,
            startAngle: -CGFloat.pi/2.0,
            endAngle: 0,
            clockwise: true)
path.addLine(to: CGPoint(x: bounds.size.width, y: bounds.size.height))

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你需要画这个路径我怎么画呢？我不是bezierPath专家：）什么是半径？