LinearGradients.swift

import UIKit

class LinearGradientLayer: CALayer {
    
    public var colorSpace = CGColorSpaceCreateDeviceRGB()
    public var colors: [CGColor]?
    public var locations: [CGFloat]?
    
    public var startPoint: CGPoint?
    public var endPoint: CGPoint?
    
    public var options: CGGradientDrawingOptions?
    
    required override init() {
        super.init()
        needsDisplayOnBoundsChange = true
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
    required override init(layer: Any) {
        super.init(layer: layer)
    }
    
    override func draw(in ctx: CGContext) {
        ctx.saveGState()

        guard let colors = colors, let gradient = CGGradient(colorsSpace: colorSpace, 
            colors: colors as CFArray, locations: locations) else { return }
        
        ctx.drawLinearGradient(
            gradient,
            start: transformPoint(startPoint ?? CGPoint(x: 0.5, y: 0)),
            end: transformPoint(endPoint ?? CGPoint(x: 0.5, y: 1)),
            options: options ?? CGGradientDrawingOptions(rawValue: 0)
        )
    }
    
    private func transformPoint(_ point: CGPoint) -> CGPoint {
        return CGPoint(x: bounds.width * point.x, y: bounds.height * point.y)
    }
}

let rectangularFrame = CGRect(x: 0, y:0, width: 750, height: 1334)
let colors = [UIColor.magenta.cgColor, UIColor.purple.cgColor, UIColor.cyan.cgColor]

let gradientViewCALayer = UIView(frame: rectangularFrame)
let gradientLayer = CAGradientLayer()
gradientLayer.frame = gradientViewCALayer.bounds
gradientLayer.colors = colors
gradientLayer.startPoint = CGPoint(x: 0.0, y: 0)
gradientLayer.endPoint = CGPoint(x: 1.0, y: 1.0)
gradientViewCALayer.layer.addSublayer(gradientLayer)

let gradientViewLinearLayer = UIView(frame: rectangularFrame)
let linearGradient = LinearGradientLayer()
linearGradient.colors = colors
linearGradient.startPoint = CGPoint(x: 0.0, y: 0)
linearGradient.endPoint = CGPoint(x: 1.0, y: 1.0)
linearGradient.frame = gradientViewLinearLayer.bounds
gradientViewLinearLayer.layer.addSublayer(linearGradient)

gradientViewCALayer
gradientViewLinearLayer