Swift version of [AKStencilButton](https://github.com/kas-kad/AKStencilButton)

ClearTextButton.swift

import UIKit

class ClearTextButton: UIButton {

	override init(frame: CGRect) {
		super.init(frame: frame)
		setup()
	}

	convenience init() {
		self.init(frame: CGRect.zero)
	}

	required init?(coder aDecoder: NSCoder) {
		fatalError("This view doesn't support NSCoding")
	}

	override func setTitleColor(_ color: UIColor?, for state: UIControlState) {
		super.setTitleColor(color, for: state)
	}

	override func layoutSubviews() {
		super.layoutSubviews()
		self.refreshMask()
	}

	private func setup() {
		self.backgroundColor = UIColor.groupTableViewBackground
		self.clipsToBounds = true
	}

	private func refreshMask() {
		self.titleLabel?.backgroundColor = UIColor.clear
		self.setTitleColor(UIColor.clear, for: .normal)

		let text: String? = self.titleLabel?.text
		let buttonSize: CGSize = self.bounds.size
		let font: UIFont? = self.titleLabel?.font

		let textSize: CGSize? = text?.size(withAttributes: [NSAttributedStringKey.font: (self.titleLabel?.font)!])

		UIGraphicsBeginImageContextWithOptions(buttonSize, false, UIScreen.main.scale)
		let ctx: CGContext? = UIGraphicsGetCurrentContext()
		ctx?.setFillColor(UIColor.white.cgColor)

		let center = CGPoint(x: buttonSize.width / 2 - (textSize?.width)! / 2, y: buttonSize.height / 2 - (textSize?.height)! / 2)

		let path = UIBezierPath(rect: CGRect(x: 0, y: 0, width: buttonSize.width, height: buttonSize.height))
		ctx?.addPath(path.cgPath)
		ctx?.fillPath()
		ctx!.setBlendMode(.destinationOut)

		text?.draw(at: center, withAttributes: [NSAttributedStringKey.font: font!])
		let viewImage: UIImage? = UIGraphicsGetImageFromCurrentImageContext()
		UIGraphicsEndImageContext()
		let maskLayer = CALayer()
		maskLayer.contents = viewImage?.cgImage as Any
		maskLayer.frame = bounds
		layer.mask = maskLayer
	}

}