UIImage+Gradient.swift

extension UIImage {
    func gradientImage(_ colors: [UIColor]) -> UIImage? {
        guard let source = withRenderingMode(.alwaysTemplate).cgImage else {
            return nil
        }
        // Create gradient
        let cgColors = colors.map({ $0.cgColor })
        let colors = cgColors as CFArray
        let space = CGColorSpaceCreateDeviceRGB()
        guard let gradient = CGGradient(colorsSpace: space,
                colors: colors, locations: nil) else {
            return nil
        }

        let renderer = UIGraphicsImageRenderer(
            bounds: CGRect(origin: .zero, size: size))
        return renderer.image { (context) in
            let context = context.cgContext
            context.translateBy(x: 0, y: size.height)
            context.scaleBy(x: 1, y: -1)

            context.setBlendMode(.normal)
            let rect = CGRect.init(x: 0, y: 0, width: size.width, height: size.height)

            // Apply gradient
            context.clip(to: rect, mask: source)
            context.drawLinearGradient(gradient, start: CGPoint(x: 0, y: 0),
                end: CGPoint(x: 0, y: size.height), options: .drawsAfterEndLocation)
        }
    }
}