article-programmaticalstyling2.swift

extension UIImage {
    static func buttonBackground(color: UIColor,
                                         borderColor: UIColor,
                                         borderWidth: CGFloat,
                                         cornerRadius: CGFloat) -> UIImage {
        let width = max(2, cornerRadius * 2)
        let size = CGSize(width: width, height: width)

        return UIGraphicsImageRenderer(size: size).image { context in
            color.setFill()
            context.fill(CGRect(origin: .zero, size: size))
        }.roundedBorder(color: borderColor,
                        width: borderWidth,
                        radius: cornerRadius)!
    }

    private func roundedBorder(color: UIColor, width: CGFloat, radius: CGFloat) -> UIImage? {
        let format = imageRendererFormat
        format.opaque = false

        return UIGraphicsImageRenderer(size: size, format: format).image { context in
            let ovalPath = UIBezierPath(roundedRect: CGRect(origin: .zero, size: size), cornerRadius: radius)
            ovalPath.addClip()
            draw(at: .zero)
            color.setStroke()
            ovalPath.lineWidth = width
            ovalPath.stroke()
        }
    }
}