How to transform a circle into a line in swift?

Question

So i have a circe with a certain pattern. I want to make transform this circle into a line. Any ideas how i could accomplish this?

I did have a look at making a UIBezierPath over the circle for then to transform this into a line without any help. I've also seen a link doing this in opencv (fast Cartesian to Polar to Cartesian in Python) but do prefer to do this in native swift.

Ive looked at creating a UIBezierPath to cover the circle and then transforming this into a line but without luck. — Lars Erik Fagernaes
– Lars Erik Fagernaes, Commented Jun 30, 2016 at 7:17
Maybe add you best try to the question and somebody can help — Idan
– Idan, Commented Jun 30, 2016 at 7:19
Do you know the diameter or the radius? If you find one of this you can find the perimeter and create a UIView of 1px height (or the thickness you want for your line) and "Perimeter" width. For example (if radius = 3): Perimeter = 2*Pi*3 = 18.85. — Victor Rius
– Victor Rius, Commented Jun 30, 2016 at 7:42
I do know the radius. Once i've created the view, should i just set the image of the view to be the circle image? It will then transform the circle image into a line? — Lars Erik Fagernaes
– Lars Erik Fagernaes, Commented Jun 30, 2016 at 7:49

Rob · Accepted Answer · 2016-06-30 07:59:50Z

1

If you don't care about the nature of the transition, the easiest way is to do CABasicAnimation, animating the path of a CAShapeLayer from one path to another. And to achieve a patterned path with CAShapeLayer is actually to have two overlapping CAShapeLayer objects, one with a dash pattern on top of one without.

let fromPath = UIBezierPath(arcCenter: view.center, radius: 100, startAngle: 0, endAngle: CGFloat(M_PI) * 2.0, clockwise: true)
let toPath = UIBezierPath()
toPath.moveToPoint(CGPoint(x: view.frame.size.width / 2.0 - CGFloat(M_PI) * 100.0, y:view.center.y))
toPath.addLineToPoint(CGPoint(x: view.frame.size.width / 2.0 + CGFloat(M_PI) * 100.0, y: view.center.y))

let shapeLayer = CAShapeLayer()
shapeLayer.path = fromPath.CGPath
shapeLayer.lineWidth = 5
shapeLayer.strokeColor = UIColor.redColor().CGColor
shapeLayer.fillColor = UIColor.clearColor().CGColor

let shapeLayer2 = CAShapeLayer()
shapeLayer2.path = fromPath.CGPath
shapeLayer2.lineWidth = 5
shapeLayer2.strokeColor = UIColor.blackColor().CGColor
shapeLayer2.fillColor = UIColor.clearColor().CGColor
shapeLayer2.lineDashPattern = [100,50]

view.layer.addSublayer(shapeLayer)
view.layer.addSublayer(shapeLayer2)

And

shapeLayer.path = toPath.CGPath
shapeLayer2.path = toPath.CGPath

CATransaction.begin()
CATransaction.setAnimationDuration(5)

let animation = CABasicAnimation(keyPath: "path")
animation.fromValue = fromPath.CGPath
animation.toValue = toPath.CGPath
shapeLayer.addAnimation(animation, forKey: nil)

let animation2 = CABasicAnimation(keyPath: "path")
animation2.fromValue = fromPath.CGPath
animation2.toValue = toPath.CGPath
shapeLayer2.addAnimation(animation, forKey: nil)

CATransaction.commit()

Yielding:

If you want more control over the nature of the transition, then you have to resort to more manual techniques, e.g. a CADisplayLink in which you manually adjust the path. But that's more complicated.

edited Jun 30, 2016 at 7:59

answered Jun 30, 2016 at 7:54

Rob

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5 Comments

Lars Erik Fagernaes Over a year ago

Hi! Thanks for such a informative and good answer! The only problem is was my formulation of the problem. The circle does not have a pre decided pattern, but is an Image, any future advice?

Rob Over a year ago

It is a non-trivial exercise to convert a random bitmap image into a shape and then proceed to that transform

Lars Erik Fagernaes Over a year ago

I might be misunderstanding but is it? I could make a color with pattern image: var color = UIColor(patternImage: image!) and set the strokeColor. But it did not work as hoped. I cant add an image to a CAShapeLayer and a CALayer does not have a path property. All i found was: stackoverflow.com/questions/5578801/…

user6248853 Over a year ago

@Rob great answer! +1 for sharing your experience.

Rob Over a year ago

@LarsErik - Yes, patternImage doesn't work as expected here, which is why I did what I did. And, no, you can just add image and expect it to transform like a UIBezierPath/CGPath can. They're completely different things.

user6248853 · Accepted Answer · 2016-06-30 09:49:56Z

try this code, The animation is not perfect, but you will be able to convert an image to a line this way. I have to say that Rob's solution above is far more superior and if I were give a choice, i would do it his way.

The below code is very self-explanatory, but if in case of any doubt, feel free to ask.

To make the animation happen, tap the yellow button.

  class ViewController: UIViewController{

    var imageView : UIImageView = {
        let image = UIImageView()
        image.translatesAutoresizingMaskIntoConstraints = false
        image.layer.cornerRadius = 120
        image.backgroundColor = UIColor.clearColor()
        image.layer.borderWidth = 3.0
        image.layer.borderColor = UIColor.blackColor().CGColor
        return image
    }()

    var animatorButton : UIButton = {
        let button = UIButton()
        button.translatesAutoresizingMaskIntoConstraints = false
        button.tintColor = UIColor.blueColor()
        button.layer.borderWidth = 3.0
        button.layer.borderColor = UIColor.blackColor().CGColor
        button.backgroundColor = UIColor.yellowColor()
        return button
    }()

    var constraintHeight = [NSLayoutConstraint]()
    override func viewDidLoad() {

        view.addSubview(imageView)
        view.addSubview(animatorButton)

        view.addConstraint(view.centerXAnchor.constraintEqualToAnchor(imageView.centerXAnchor))
        view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:[imageView(240)]", options: NSLayoutFormatOptions(), metrics: nil, views: ["imageView": imageView]))

        self.constraintHeight = NSLayoutConstraint.constraintsWithVisualFormat("V:|-100-[imageView(240)]", options: NSLayoutFormatOptions(), metrics: nil, views: ["imageView": imageView])
        view.addConstraints(constraintHeight)


        view.addConstraint(animatorButton.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor))
        view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-450-[Button(40)]", options: NSLayoutFormatOptions(), metrics: nil, views: ["Button": animatorButton]))
        view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[Button]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["Button": animatorButton]))


        animatorButton.addTarget(self, action: #selector(ViewController.animateImageToLine), forControlEvents: .TouchUpInside)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    func animateImageToLine() {

        view.removeConstraints(constraintHeight)
        constraintHeight = NSLayoutConstraint.constraintsWithVisualFormat("V:|-100-[imageView(3)]", options: NSLayoutFormatOptions(), metrics: nil, views: ["imageView": imageView])
        view.addConstraints(constraintHeight)
        UIView.animateWithDuration(0.3, animations: {
            self.imageView.layer.cornerRadius = 0
               self.view.layoutIfNeeded()


            }, completion: { success in
                self.imageView.backgroundColor = UIColor.blackColor()
                self.imageView.layer.borderWidth = 3.0
        })

    }
    }

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