iOS Circular Gradient - ios

Question

I have a task to draw the line with a circular gradient (colour should change by the circle) and then add animation. Now I draw 360 layers with a certain interval and different colours.
var colours: [UIColor] = [UIColor]()
var startAngle = CGFloat(-0.5 * Double.pi)
var index = 0
func drawLayers() {
let smallAngle = (1.5 * CGFloat.pi - (-0.5 * CGFloat.pi)) / 360
if index < colours.count { //colours.count = 360
let endAngle = startAngle + smallAngle
let circlePath = UIBezierPath(arcCenter: .init(x: 100, y: 100), radius: 100, startAngle: startAngle, endAngle: endAngle, clockwise: true)
startAngle = endAngle
let shapeLayer = CAShapeLayer()
shapeLayer.path = circlePath.cgPath
shapeLayer.fillColor = UIColor.clear.cgColor
shapeLayer.strokeColor = colours[index].cgColor
shapeLayer.lineWidth = 8
view.layer.addSublayer(shapeLayer)
index += 1
Timer.scheduledTimer(
withTimeInterval: 0.004,
repeats: false) { (_) in
self.drawLayers()
}
}
}
Something like that but with linear animation
Can anyone tell me how to do it right?

Answer 1

iOS has circular (conic) gradients built in now. So I would just ask for the gradient, once, and then animate a single path used as a mask. That’s just two layers, much less work, true animation, and a true gradient.
Example:
Here's my test code; change the colors and numbers as desired:
let grad = CAGradientLayer()
grad.type = .conic
grad.colors = [UIColor.red.cgColor, UIColor.green.cgColor, UIColor.red.cgColor]
grad.startPoint = CGPoint(x: 0.5, y: 0.5)
grad.frame = CGRect(x: 100, y: 100, width: 200, height: 200)
self.view.layer.addSublayer(grad)
let c = CAShapeLayer()
let p = UIBezierPath(ovalIn: CGRect(x: 20, y: 20, width: 160, height: 160))
c.path = p.cgPath
c.fillColor = UIColor.clear.cgColor
c.strokeColor = UIColor.black.cgColor
c.lineWidth = 8
grad.mask = c
c.strokeEnd = 0
To make the animation happen, just say:
c.strokeEnd = 1