BottomBarView.swift

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport

let BALL: CGFloat = 100

class MyViewController : UIViewController {
    override func loadView() {
        let view = UIView()
        view.backgroundColor = UIColor.black

        let label = UILabel()
        label.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
        label.text = "Hello World!"
        label.textColor = .black
        
        view.addSubview(label)

        let bottom = BottomBarView()
        bottom.translatesAutoresizingMaskIntoConstraints = false
//        bottom.radius = 30
        bottom.frame = CGRect.zero
        bottom.backgroundColor = UIColor.red

        let button = UIView()
        button.translatesAutoresizingMaskIntoConstraints = false
        button.backgroundColor = UIColor.yellow
        button.layer.cornerRadius = 90/2.0

        view.addConstraint(NSLayoutConstraint(item: button, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 90))
        view.addConstraint(NSLayoutConstraint(item: button, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 90))
        view.addConstraint(NSLayoutConstraint(item: button, attribute: .top, relatedBy: .equal, toItem: bottom, attribute: .top, multiplier: 1, constant: 5.0))
        view.addConstraint(NSLayoutConstraint(item: button, attribute: .centerX, relatedBy: .equal, toItem: view, attribute: .centerX, multiplier: 1, constant: 0))

        view.addSubview(button)

        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailing, multiplier: 1, constant: 0))
        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1, constant: 0))
        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottom, multiplier: 1, constant: 0))
        view.addConstraint(NSLayoutConstraint(item: bottom, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 131))

        view.addSubview(bottom)

        self.view = view

    }

}

final class BottomBarView: UIView {

  //private let MAGIC_NUMBER: CGFloat = 0.552284749831
  private let MAGIC_NUMBER: CGFloat = 0.5

  var radius: CGFloat = 30
  var ballRadius: CGFloat = BALL

  override func layoutSubviews() {
    super.layoutSubviews()
    roundCorners()
  }

  var controlPoints: [CGPoint] = []

  override func draw(_ rect: CGRect) {
    super.draw(rect)

    controlPoints.forEach { controlPoint in
      if let context = UIGraphicsGetCurrentContext() {
        context.addEllipse(in: CGRect(x: controlPoint.x, y: controlPoint.y, width: 10.0, height: 10.0))
        context.setFillColor(UIColor.white.cgColor)
        context.fillPath()
      }
    }

  }

  func roundCorners() {

    if layer.mask == nil && radius != 0 {

      let rect = self.bounds

      let path = UIBezierPath()

      path.move(to: CGPoint(x: rect.minX, y: rect.maxY))

      path.addArc(withCenter: CGPoint(x: rect.minX + radius, y: rect.minY + radius), radius: radius, startAngle: .pi, endAngle: .pi * 3 / 2, clockwise: true)

      path.addArc(withCenter: CGPoint(x: rect.maxX/2 - ballRadius/2 - radius, y: rect.minY + radius), radius: radius, startAngle: .pi * 3 / 2, endAngle: 2 * .pi, clockwise: true)

      path.addArc(withCenter: CGPoint(x: rect.maxX/2, y: ballRadius/2), radius: ballRadius/2, startAngle: .pi, endAngle: .pi * 2, clockwise: false)

      path.addArc(withCenter: CGPoint(x: rect.maxX/2 + radius + ballRadius/2, y: rect.minY + radius), radius: radius, startAngle: .pi, endAngle: .pi * 3 / 2, clockwise: true)

      path.addArc(withCenter: CGPoint(x: rect.maxX - radius, y: rect.minY + radius), radius: radius, startAngle: .pi * 3 / 2, endAngle: 2 * .pi, clockwise: true)

      path.addLine(to: CGPoint(x: rect.maxX, y: rect.maxY))

      path.close()

      let maskLayer = CAShapeLayer()
      maskLayer.path = path.cgPath
      layer.mask = maskLayer

    }

  }

}

// Present the view controller in the Live View window
let viewController = MyViewController()
viewController.preferredContentSize = CGSize(width: 500, height: 500)
PlaygroundPage.current.liveView = viewController