UIColor Scaling

gistfile1.txt

// Based upon https://web.archive.org/web/20150227031931/http://www.codelib.net/home/jkm/hexcolorscale.html

extension UIColor {
    func scaled(by factor: CGFloat) -> UIColor {
        let components = self.cgColor.components
        var r: CGFloat = (components?[0] ?? 0.0) * 255
        var g: CGFloat = (components?[1] ?? 0.0) * 255
        var b: CGFloat = (components?[2] ?? 0.0) * 255
        let alpha: CGFloat = components?[3] ?? 1.0

        r = round(relsizeinv(a: relsize(a: r) * factor))
        g = round(relsizeinv(a: relsize(a: g) * factor))
        b = round(relsizeinv(a: relsize(a: b) * factor))

        return UIColor(red: r / 255, green: g / 255, blue: b / 255, alpha: alpha)
    }

    private static let max255: CGFloat = 255
    private func relsize(a: CGFloat) -> CGFloat {
        guard a != UIColor.max255 else { return UIColor.max255 }
        return a / (UIColor.max255 - a)
    }

    private func relsizeinv(a: CGFloat) -> CGFloat {
        guard a != UIColor.max255 else { return UIColor.max255 }

        return UIColor.max255 * a / (1 + a)
    }
}