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()

     }