Inside gradient color UIBezierPath

Question

I need to fill my bezier path with a gradient color. I can fill the background on the graph but not the content of the bezier. Any idea why?

//: Playground - noun: a place where people can play

import Foundation
import UIKit
import CoreGraphics
import QuartzCore

class DemoView: UIView {
    override func draw(_ rect: CGRect) {
        let origin = CGPoint(x: frame.size.width / 2, y: frame.size.height / 2)
        let radius = frame.size.width / 2

//        self.createCircle(origin: origin, radius: radius)
        self.addLinesInCircle(origin: origin, radius: radius)
    }

    func createCircle(origin: CGPoint, radius: CGFloat) {
        let path = UIBezierPath()
        path.addArc(withCenter: origin, radius: radius, startAngle: 0, endAngle: CGFloat(2 * Double.pi), clockwise: true)
        path.close()
        UIColor.clear.setFill()
        path.fill()
    }

    func addLinesInCircle(origin: CGPoint, radius: CGFloat) {
        let bezier = UIBezierPath()
        let incrementAngle: CGFloat = CGFloat.pi / 24
        let ratios: [CGFloat] = [3/6, 5/6, 3/6, 1/6, 5/6, 2/6, 4/6, 2/6, 4/6, 4/6, 4/6, 4/6,
                                 3/6, 5/6, 3/6, 1/6, 5/6, 2/6, 4/6, 2/6, 4/6, 4/6, 4/6, 4/6,
                                 3/6, 5/6, 3/6, 1/6, 5/6, 2/6, 4/6, 2/6, 4/6, 4/6, 4/6, 4/6,
                                 3/6, 5/6, 3/6, 1/6, 5/6, 2/6, 4/6, 2/6, 4/6, 4/6, 4/6, 4/6]

        for (index, ratio) in ratios.enumerated() {
            let point = CGPoint(x: origin.x + cos(CGFloat(index) * incrementAngle) * radius * ratio,
                                y: origin.y + sin(CGFloat(index) * incrementAngle) * radius * ratio)
            if index == 0 {
                bezier.move(to: point)
            } else {
                bezier.addLine(to: point)
            }
        }
        bezier.close()

        let layer = CAGradientLayer()
            layer.frame = bezier .bounds
            layer.colors = [UIColor.red.cgColor,UIColor.blue.cgColor,UIColor.yellow.cgColor ,UIColor.black.cgColor]

        let mask = CAShapeLayer()
            mask.frame = bezier.bounds
            mask.path = bezier.cgPath
            mask.fillColor = UIColor.black.cgColor

        layer.mask = mask

        self.layer.addSublayer(layer)
        self.layer.addSublayer(mask)
    }
}

let demoView = DemoView(frame: CGRect(x: 0, y: 0, width: 1000, height: 1000))

Here is the result. I need the exact opposite, assign the gradient to the bezier. (I directly used the xcode playground in order to test)

Answer 1

One option is to use CGGradient along with using the bezier path as a clipping region. No need for layers.

Replace everything after closing the path with:

let gradient = CGGradient(colorsSpace: nil, colors: [UIColor.red.cgColor,UIColor.blue.cgColor,UIColor.yellow.cgColor ,UIColor.black.cgColor] as CFArray, locations: nil)!

let ctx = UIGraphicsGetCurrentContext()!
ctx.saveGState()

// Clip to the path
bezier.addClip() 
// Draw the gradient in the clipped region
ctx.drawLinearGradient(gradient, start: CGPoint(x: 0, y: 0), end: CGPoint(x: 0, y: frame.height), options: [])

ctx.restoreGState()