Rotate a ImageView around a pivot point in iOS

Question

Records and Rotate seek-bar

I have an App screen below to record(max 30s) audio.

1. How can I rotate smoothly the little circle as seek-bar on dotted circle line while recording the audio?
2. How can I fill the dotted line while the little circle rotates along the line.

Thanks.

Answer 1

Answer is having both ways to do so using a PanGesture and automatically using a Timer .

1. Using UIPanGestureRecognizer:

You can achieve this using UIPanGestureRecognizer . circleView is your mainView and nob is another view or imageView which will move outside the circleView

panGesture = UIPanGestureRecognizer(target: self, action: #selector(panHandler(_:)))
nob.addGestureRecognizer(panGesture)

Definition of panHandler(_ :)

@objc func panHandler(_ gesture: UIPanGestureRecognizer) {
    let point = gesture.location(in: self)
    updateForPoints(point)
}

And here is the core logic how will it work.

func updateForPoints(_ point: CGPoint) {

    /*
     * Parametric equation of circle
     * x = a + r cos t
     * y = b + r sin ⁡t
     * a, b are center of circle
     * t (theta) is angle
     * x and y will be points which are on circumference of circle
     *
               270
                |
            _   |   _
                |
     180 -------o------- 360
                |
            +   |   +
                |
               90
     *
     */

    let centerOffset =  CGPoint(x: point.x - circleView.frame.midX, y: point.y - circleView.frame.midY)

    let a: CGFloat = circleView.center.x
    let b: CGFloat = circleView.center.y
    let r: CGFloat = circleView.layer.cornerRadius - 2.5
    let theta: CGFloat = atan2(centerOffset.y, centerOffset.x)
    let newPoints = CGPoint(x: a + r * cos(theta), y: b + r * sin(theta))

    var rect = nob.frame
    rect.origin = newPoints
    nob.center = newPoints
}

2. Automatically move using Timer

let totalSeconds: Int = 30 // You can change it whatever you want
var currentSecond: Int = 1
var timer: Timer?


func degreesToRadians(_ degree: CGFloat) -> CGFloat {
     /// Will convert the degree (180°) to radians (3.14)
     return degree * .pi / 180
}

func angleFromSeconds(_ seconds: Int) -> CGFloat {
     /// Will calculate the angle for given seconds
     let aSliceAngle = 360.0 / CGFloat(totalSeconds)
     let angle = aSliceAngle * CGFloat(seconds) - 90
     return angle
}

/// ------------- TIMER METHODS ------------- ///

func startTimer() {
     stopTimer()
     timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(timeDidUpdate(_ :)), userInfo: nil, repeats: true)
     timeDidUpdate(timer!)
}

func stopTimer() {
     currentSecond = 1
     timer?.invalidate()
     timer = nil
}

@objc func timeDidUpdate(_ t: Timer) {
      let angle = angleFromSeconds(currentSecond)
      let theta = degreesToRadians(angle)
      updateAngle(theta: theta, animated: true)
      currentSecond += 1

      if currentSecond > totalSeconds {
         self.stopTimer()
      }
}

/// --------------- MAIN METHOD -------------- ///
func updateAngle(theta: CGFloat, animated: Bool) {

     let a: CGFloat = circleView.center.x
     let b: CGFloat = circleView.center.y
     let r: CGFloat = circleView.layer.cornerRadius
     let newPoints = CGPoint(x: a + r * cos(theta), y: b + r * sin(theta))

     var rect = nob.frame
     rect.origin = newPoints

     if animated {
         UIView.animate(withDuration: 0.1, animations: {
         self.nob.center = newPoints

         /// Uncomment if your nob is not a circle and you want to maintain the angle too
         // self.nob.transform = CGAffineTransform.identity.rotated(by: theta)
         })
     }
     else {
         nob.center = newPoints

         /// Uncomment if your nob is not a circle and you want to maintain the angle too
         //nob.transform = CGAffineTransform.identity.rotated(by: theta)
     }
}

Answer 2

If I understand you correctly, you want to have nice animated progress indicator. There is of course lot of ways how to achiev that. I am going to provide you little bit complex solution, what will give you full control about animation - change speed during animation, starting from different point, pause at any time, or even revert the animation.

1) Let start with full working example. We need few properties:

class ViewController: UIViewController {

   var displayLink:CADisplayLink?
   var circlePathLayer = CAShapeLayer()
   var dottedLine = CAShapeLayer()
   var beginTime:TimeInterval?

2) Define display link. It is pretty fast trigger, what sending event on each display refresh - ie 60 times per second, it can be set manually and this progress func will handle the correct state of your progress view

override func viewDidLoad() {
    super.viewDidLoad()
    view.backgroundColor = .blue
    beginTime = Date().timeIntervalSinceReferenceDate
    displayLink = CADisplayLink(target: self, selector: #selector(progress))
    displayLink?.add(to: RunLoop.main, forMode: .defaultRunLoopMode)

3) Define your circle path, what should be followed

let path = UIBezierPath(arcCenter: view.center, radius: view.center.x - 20, startAngle: -CGFloat.pi / 2, endAngle: CGFloat.pi * 2 - CGFloat.pi / 2, clockwise: true)

4) Define dotted line and default animation for the line. There is timeOffset , speed and beginTime properties what follows CAMediaTimming protocol, and we don't want to animate anything yet, and set the drawing of this layer to the zero - begining state

        dottedLine.timeOffset = 0
        dottedLine.speed = 0
        dottedLine.duration = 1
        dottedLine.beginTime = dottedLine.convertTime(CACurrentMediaTime(), from: nil)
        dottedLine.repeatCount = 1
        dottedLine.autoreverses = false

        dottedLine.fillColor = nil
        dottedLine.fillMode = kCAFillModeBoth
        dottedLine.strokeStart = 0.0
        dottedLine.strokeColor = UIColor.white.cgColor
        dottedLine.lineWidth = 5.0
        dottedLine.lineJoin = kCALineJoinMiter
        dottedLine.lineDashPattern = [10,10]
        dottedLine.lineDashPhase = 3.0
        dottedLine.path = path.cgPath

        let pathAnimation = CAKeyframeAnimation(keyPath: "strokeEnd")
        pathAnimation.duration = 1
        pathAnimation.isRemovedOnCompletion = false
        pathAnimation.autoreverses = true
        pathAnimation.values = [0, 1]
        pathAnimation.fillMode = kCAFillModeBoth
        dottedLine.add(pathAnimation, forKey: "strokeEnd")
        view.layer.addSublayer(dottedLine)

5) Same for small circle

        let circlePath = UIBezierPath(arcCenter: CGPoint(x: 0, y: 0), radius: 10, startAngle: 0, endAngle:CGFloat.pi * 2, clockwise: true)
        let shapeLayer = CAShapeLayer()
        shapeLayer.path = circlePath.cgPath
        shapeLayer.fillColor = UIColor.white.cgColor
        shapeLayer.strokeColor = nil

        circlePathLayer.addSublayer(shapeLayer)
        circlePathLayer.timeOffset = 0
        circlePathLayer.speed = 0
        circlePathLayer.beginTime = circlePathLayer.convertTime(CACurrentMediaTime(), from: nil)
        circlePathLayer.duration = 1
        circlePathLayer.repeatCount = 1
        circlePathLayer.autoreverses = false
        circlePathLayer.fillColor = nil
        view.layer.addSublayer(circlePathLayer)

        let circleAnimation = CAKeyframeAnimation(keyPath: "position")
        circleAnimation.duration = 1
        circleAnimation.isRemovedOnCompletion = false
        circleAnimation.autoreverses = false
        circleAnimation.values = [0, 1]
        circleAnimation.fillMode = kCAFillModeBoth
        circleAnimation.path = path.cgPath
        circlePathLayer.add(circleAnimation, forKey: "position")        
}

6) Finally the progress function, it is called very often and at this point you going to set progress position - in my example is set to 30 seconds, but you can add here some conditions to do not change time offset - pause, or change it with different amount to handle the speed, or put it back.

 @objc func progress() {
        let time = Date().timeIntervalSinceReferenceDate - (beginTime ?? 0)
        circlePathLayer.timeOffset = time / 30
        dottedLine.timeOffset = time / 30
    }

7) As soon as you will finish your animations, do not forget to release resources and invalidate display link

displayLink?.invalidate()