UIBezierPath with color gradient

Question

I\'ve got an question about UIBezierPath.

For example I\'ve got this path:

Now I want to have

Answer 1

Another take on Oleg's answer regarding the saturation (white gradient) that I find more pleasing, and in Swift (3).

You can add steps to the gradient if you want a bigger white circle (ex a 2nd white step at 0.2)

import UIKit

class HSView: UIView {
    override func draw(_ rect: CGRect) {
        let arcStep = 2 * CGFloat.pi / 360
        let isClockwise = false
        let x = rect.width / 2
        let y = rect.height / 2
        let radius = min(x, y) / 2
        let ctx = UIGraphicsGetCurrentContext()
        ctx?.setLineWidth(2 * radius)

        for i in 0..<360 {
            let color = UIColor(hue: CGFloat(i)/360, saturation: 1, brightness: 1, alpha: 1)
            let startAngle = CGFloat(i) * arcStep
            let endAngle = startAngle + arcStep + 0.02

            ctx?.setStrokeColor(color.cgColor)
            ctx?.addArc(center: CGPoint(x: x, y: y), radius: radius, startAngle: startAngle, endAngle: endAngle, clockwise: isClockwise)
            ctx?.strokePath()
        }

        let gradient = CGGradient(colorsSpace: UIColor.white.cgColor.colorSpace,
                                  colors: [
                                    UIColor.white.cgColor,
                                    UIColor.white.withAlphaComponent(0).cgColor,
                                    ] as CFArray,
                                  locations: [
                                    0,
                                    1,
            ]
        )
        ctx?.drawRadialGradient(gradient!, startCenter: CGPoint(x: x, y: y), startRadius: 0, endCenter: CGPoint(x: x, y: y), endRadius: 2 * radius, options: .drawsAfterEndLocation)
    }
}