ProgressiveBlurView from My top 3 design “Kisses” I like to add to every app

ProgressiveBlurView.swift

private final class VariableBlurUIView: UIVisualEffectView {
    override func layoutSubviews() {
        super.layoutSubviews()

        let filter = (NSClassFromString("CAFilter") as! NSObject.Type)
            .perform(NSSelectorFromString("filterWithType:"), with: "variableBlur")!
            .takeUnretainedValue() as! NSObject

        filter.setValue(20, forKey: "inputRadius")
        filter.setValue(makeMaskImage(), forKey: "inputMaskImage")
        filter.setValue(true, forKey: "inputNormalizeEdges")

        subviews.first?.layer.filters = [filter]
    }

    private func makeMaskImage() -> CGImage {
        let gradient = CIFilter.linearGradient()
        gradient.color0 = CIColor.white
        gradient.color1 = CIColor.clear
        gradient.point0 = CGPoint(x: 0, y: bounds.height)
        gradient.point1 = CGPoint(x: 0, y: 0)

        return CIContext().createCGImage(
            gradient.outputImage!,
            from: CGRect(origin: .zero, size: bounds.size)
        )!
    }
}