Arc progress

ArcProgress.swift

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

class ArcProgressViewController : UIViewController {

    private lazy var backgroundLayer: CAShapeLayer = {
        let layer = CAShapeLayer()
        layer.frame = CGRect(x: 25, y: 25, width: 325, height: 325)
        layer.fillColor = UIColor.lightGray.cgColor
        return layer
    }()

    private let progressLayer: CAShapeLayer = {
        let layer = CAShapeLayer()
        layer.fillColor = UIColor.darkGray.cgColor
        return layer
    }()

    private var currentProgress: CGFloat = 0 {
        didSet {
            drawProgress(currentProgress)
        }
    }

    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white
        self.view = view

        drawBackgroundCircle()
        createDisplayLink()
    }

    /// Create the dispaly link to update the screen
    private func createDisplayLink() {
        let displaylink = CADisplayLink(target: self, selector: #selector(handleDisplayUpdate))
        displaylink.add(to: .current, forMode: .default)
    }

    /// Update the screen
    @objc private func handleDisplayUpdate(displayLink: CADisplayLink) {
        currentProgress += 0.005
        // Wrap around once we get to 1 for an endless loop
        if currentProgress > 1 {
            currentProgress = 0
        }
    }

    /// Draws the circle behind the progress layer
    private func drawBackgroundCircle() {
        drawPath(in: backgroundLayer, progress: 1)
        view.layer.addSublayer(backgroundLayer)
    }

    /// Updates the progressLayer with the current progress
    private func drawProgress(_ progress: CGFloat) {
        guard progress >= 0, progress <= 1 else {
            return
        }
        if progressLayer.frame == .zero {
            let diff: CGFloat = 10
            var frame = backgroundLayer.frame
            frame.origin.x += diff
            frame.origin.y += diff
            frame.size.width -= diff * 2
            frame.size.height -= diff * 2
            progressLayer.frame = frame
            progressLayer.transform = CATransform3DMakeRotation(CGFloat.pi/180 * 270, 0, 0, 1.0);
            view.layer.addSublayer(progressLayer)
        }
        drawPath(in: progressLayer, progress: progress)
    }

    /// Draws an arc of progress in the layer that's passed in
    private func drawPath(in layer: CAShapeLayer, progress: CGFloat) {
        let frame = layer.frame
        let startPoint = CGPoint(x: frame.width, y: frame.height / 2.0)
        let centerPoint = CGPoint(x: frame.width / 2.0, y: frame.height / 2.0)
        let startAngle = CGFloat(0)
        let endAngle = progress * CGFloat.pi * 2

        let path = UIBezierPath()
        path.move(to: centerPoint)
        path.addLine(to: startPoint)
        path.addArc(withCenter: centerPoint,
                    radius: frame.width / 2.0,
                    startAngle: startAngle,
                    endAngle: endAngle,
                    clockwise: true)
        path.addLine(to: centerPoint)
        path.close()
        layer.path = path.cgPath
    }
}

// Present the view controller in the Live View window
PlaygroundPage.current.liveView = ArcProgressViewController()