(Ab)using UIVisualEffectView effect settings

UIVisualEffect.swift

extension UIVisualEffectView {
    
    private var filterLayer: CALayer? {
        return layer.sublayers?.first
    }
    
    private var blurFilter: NSObject? {
        return filterLayer?
            .filters?.flatMap({ $0 as? NSObject })
            .first(where: { $0.value(forKey: "name") as? String == "gaussianBlur" })
    }

    private var saturationFilter: NSObject? {
        return filterLayer?
            .filters?.flatMap({ $0 as? NSObject })
            .first(where: { $0.value(forKey: "name") as? String == "colorSaturate" })
    }

    var blurRadius: CGFloat {
        get {
            return blurFilter?.value(forKey: "inputRadius") as? CGFloat ?? 0
        }
        set {
            blurFilter?.setValue(newValue, forKey: "inputRadius")
            if newValue == 0 { scale = 1 }
        }
    }
    
    var saturationAmount: CGFloat {
        get {
            return saturationFilter?.value(forKey: "inputAmount") as? CGFloat ?? 1
        }
        set {
            saturationFilter?.setValue(newValue, forKey: "inputAmount")
        }
    }
    
    var scale: CGFloat? {
        get {
            return filterLayer?.value(forKey: "scale") as? CGFloat
        }
        set {
            filterLayer?.setValue(newValue, forKey: "scale")
        }
    }
    
    var opacity: Float? {
        get {
            return layer.sublayers?.last?.opacity
        }
        set {
            layer.sublayers?.last?.opacity = newValue ?? 0
        }
    }
    
}