Show part of a circle - swift

Question

i want to display an arbitray part of a circle.
I know how to get a round View using layer.cornerRadius now i want to see only a part of that circle(for any given radiant value). It would be ok, if the rest of it would be simply hidden beneath something white.
Any ideas, how to achieve that?
edit:
i have written a class for my View:
class Circle:UIView {
var rad = 0
let t = CGFloat(3.0)
override func draw(_ rect: CGRect) {
super.draw(rect)
let r = self.frame.width / CGFloat(2)
let center = CGPoint(x: r, y: r)
let path = UIBezierPath()
path.move(to: CGPoint(x: t, y: r))
path.addLine(to: CGPoint(x: 0.0, y: r))
path.addArc(withCenter: center, radius: CGFloat(r), startAngle: CGFloat(Double.pi), endAngle: CGFloat(Double.pi+rad), clockwise: true)
let pos = path.currentPoint
let dx = r - pos.x
let dy = r - pos.y
let d = sqrt(dx*dx+dy*dy)
let p = t / d
path.addLine(to: CGPoint(x: pos.x + p * dx, y: pos.y + p * dy))
path.addArc(withCenter: center, radius: r-t, startAngle: CGFloat(Double.pi+rad), endAngle: CGFloat(Double.pi), clockwise: false)
UIColor(named: "red")?.setFill()
path.fill()
}
}
public func setRad(perc:Double) {
rad = Double.pi * 2 * perc
}
in my view controller i call
circleView.layer.cornerRadius = circleView.frame.size.width / 2
circleView.clipsToBounds = true
circleView.layer.borderWidth = 1
circleView.layer.borderColor = UIColor.darkGray.cgColor
circleView.layer.shadowColor = UIColor.black.cgColor
circleView.layer.shadowOpacity = 1
circleView.layer.shadowOffset = CGSize.zero
circleView.layer.shadowRadius = 3
circleView.layer.masksToBounds = false
circleView.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(self.onTap)))
now i get the full square View with a black circle from the corner and the red arc that i draw. If necessary i will post a picture tomorrow

Answer 1

One way to do it is to draw a UIBezierPath.
If you just want an arc, you can call the init(arcCenter:radius:startAngle:endAngle:clockwise:) initializer. Remember to specify the start and end angles in radians!
After that, you can set the stroke color and call stroke
If you want a sector of a circle, you can create a UIBezierPath with the parameterless initializer, then move(to:) the center of the circle, and then addLine(to:) the start of the arc. You can probably calculate where this point is with a bit of trigonometry. After that, call addArc like I described above, then addLine(to:) the point where you started. After that, you can fill the path.