How to draw rounded rect that wraps around circular button?

Question

I want to design the highlighted portion of curve of the below screen snapshot using bezier path in swift.

Answer 1

It’s just a little trigonometry to figure out the arcs around that button in the bottom right hand corner, e.g.

func updatePath() {
    let buttonCenter = CGPoint(x: bounds.maxX - circleRadius, y: bounds.maxY - circleRadius)

    circleShapeLayer.path = UIBezierPath(arcCenter: buttonCenter, radius: circleRadius, startAngle: 0, endAngle: .pi * 2, clockwise: true).cgPath // red

    let angle1 = acos((circleRadius - cornerRadius) / (circleRadius + spaceRadius + cornerRadius))
    let angle2 = acos((circleRadius - bottomDistance - cornerRadius) / (circleRadius + spaceRadius + cornerRadius))

    let arc1Center = CGPoint(x: bounds.maxX - cornerRadius,
                             y: buttonCenter.y - (circleRadius + cornerRadius + spaceRadius) * sin(angle1))

    let path = UIBezierPath()

    path.move(to: CGPoint(x: bounds.maxX, y: bounds.minY + cornerRadius))
    path.addArc(withCenter: arc1Center, radius: cornerRadius, startAngle: 0, endAngle: .pi / 2 + (.pi / 2 - angle1), clockwise: true) // blue
    path.addArc(withCenter: buttonCenter, radius: circleRadius + spaceRadius, startAngle: 2 * .pi - angle1, endAngle: .pi / 2 + angle2, clockwise: false) // green

    let arc2Center = CGPoint(x: buttonCenter.x - (circleRadius + cornerRadius + spaceRadius) * sin(angle2), y: bounds.maxY - bottomDistance - cornerRadius)

    path.addArc(withCenter: arc2Center, radius: cornerRadius, startAngle: -(.pi / 2 - angle2), endAngle: .pi / 2, clockwise: true) // yellow
    path.addArc(withCenter: CGPoint(x: bounds.minX + cornerRadius, y: bounds.maxY - (bottomDistance + cornerRadius)), radius: cornerRadius, startAngle: .pi / 2, endAngle: .pi, clockwise: true) // cyan
    path.addArc(withCenter: CGPoint(x: bounds.minX + cornerRadius, y: bounds.minY + cornerRadius), radius: cornerRadius, startAngle: .pi, endAngle: .pi * 3 / 2, clockwise: true) // white
    path.addArc(withCenter: CGPoint(x: bounds.maxX - cornerRadius, y: bounds.minY + cornerRadius), radius: cornerRadius, startAngle: .pi * 3 / 2, endAngle: 2 * .pi, clockwise: true) // black
    path.close()

    backgroundShapeLayer.path = path.cgPath
}

Yielding:

Or, if you want to match the above strokes, here it is color coded to the comments in the code above:

---

For example:

@IBDesignable
class BackgroundView: UIView {
    @IBInspectable var cornerRadius:   CGFloat = 10 { didSet { setNeedsLayout() } }
    @IBInspectable var spaceRadius:    CGFloat = 10 { didSet { setNeedsLayout() } }
    @IBInspectable var circleRadius:   CGFloat = 50 { didSet { setNeedsLayout() } }
    @IBInspectable var bottomDistance: CGFloat = 30 { didSet { setNeedsLayout() } }

    private let backgroundShapeLayer: CAShapeLayer = {
        let shapeLayer = CAShapeLayer()
        shapeLayer.fillColor = UIColor.white.cgColor
        shapeLayer.strokeColor = UIColor.clear.cgColor
        return shapeLayer
    }()

    private let circleShapeLayer: CAShapeLayer = {
        let shapeLayer = CAShapeLayer()
        shapeLayer.fillColor = UIColor.white.cgColor
        shapeLayer.strokeColor = UIColor.clear.cgColor
        return shapeLayer
    }()

    override init(frame: CGRect = .zero) {
        super.init(frame: frame)
        configure()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        configure()
    }

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

private extension BackgroundView {

    func configure() {
        layer.addSublayer(circleShapeLayer)
        layer.addSublayer(backgroundShapeLayer)
    }

    func updatePath() {
        let buttonCenter = CGPoint(x: bounds.maxX - circleRadius, y: bounds.maxY - circleRadius)

        circleShapeLayer.path = UIBezierPath(arcCenter: buttonCenter, radius: circleRadius, startAngle: 0, endAngle: .pi * 2, clockwise: true).cgPath

        let angle1 = acos((circleRadius - cornerRadius) / (circleRadius + spaceRadius + cornerRadius))
        let angle2 = acos((circleRadius - bottomDistance - cornerRadius) / (circleRadius + spaceRadius + cornerRadius))

        let arc1Center = CGPoint(x: bounds.maxX - cornerRadius,
                                 y: buttonCenter.y - (circleRadius + cornerRadius + spaceRadius) * sin(angle1))

        let path = UIBezierPath()

        path.move(to: CGPoint(x: bounds.maxX, y: bounds.minY + cornerRadius))
        path.addArc(withCenter: arc1Center, radius: cornerRadius, startAngle: 0, endAngle: .pi / 2 + (.pi / 2 - angle1), clockwise: true)
        path.addArc(withCenter: buttonCenter, radius: circleRadius + spaceRadius, startAngle: 2 * .pi - angle1, endAngle: .pi / 2 + angle2, clockwise: false)

        let arc2Center = CGPoint(x: buttonCenter.x - (circleRadius + cornerRadius + spaceRadius) * sin(angle2), y: bounds.maxY - bottomDistance - cornerRadius)

        path.addArc(withCenter: arc2Center, radius: cornerRadius, startAngle: -(.pi / 2 - angle2), endAngle: .pi / 2, clockwise: true)
        path.addArc(withCenter: CGPoint(x: bounds.minX + cornerRadius, y: bounds.maxY - (bottomDistance + cornerRadius)), radius: cornerRadius, startAngle: .pi / 2, endAngle: .pi, clockwise: true)
        path.addArc(withCenter: CGPoint(x: bounds.minX + cornerRadius, y: bounds.minY + cornerRadius), radius: cornerRadius, startAngle: .pi, endAngle: .pi * 3 / 2, clockwise: true)
        path.addArc(withCenter: CGPoint(x: bounds.maxX - cornerRadius, y: bounds.minY + cornerRadius), radius: cornerRadius, startAngle: .pi * 3 / 2, endAngle: 2 * .pi, clockwise: true)
        path.close()

        backgroundShapeLayer.path = path.cgPath
    }
}