override func draw(_ rect: CGRect) { let path = UIBezierPath() // 起点
path.move(to: CGPoint(x: , y: )) // 完善曲线:两个控制点
// path.addCurve(to: <#T##CGPoint#>, controlPoint1: <#T##CGPoint#>, controlPoint2: <#T##CGPoint#>) // 完善曲线:一个控制点
path.addQuadCurve(to: CGPoint(x:,y:), controlPoint: CGPoint(x: , y: )) // 描边渲染
path.stroke()
}