Drawing an NSImage with rounded corners in Swift

NSImage+RoundedCorners.swift

// This extension is a port of @venj's solution from 2011
// https://github.com/venj/Cocoa-blog-code/blob/master/Round%20Corner%20Image/Round%20Corner%20Image/NSImage%2BRoundCorner.m
extension NSImage {

    func roundCorners(withRadius radius: CGFloat) -> NSImage {
        let rect = NSRect(origin: NSPoint.zero, size: size)
        if
            let cgImage = self.cgImage,
            let context = CGContext(data: nil,
                                width: Int(size.width),
                                height: Int(size.height),
                                bitsPerComponent: 8,
                                bytesPerRow: 4 * Int(size.width),
                                space: CGColorSpaceCreateDeviceRGB(),
                                bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue) {
            context.beginPath()
            context.addPath(CGPath(roundedRect: rect, cornerWidth: radius, cornerHeight: radius, transform: nil))
            context.closePath()
            context.clip()
            context.draw(cgImage, in: rect)

            if let composedImage = context.makeImage() {
                return NSImage(cgImage: composedImage, size: size)
            }
        }

        return self
    }

}

fileprivate extension NSImage {

    var cgImage: CGImage? {
        var rect = CGRect.init(origin: .zero, size: self.size)
        return self.cgImage(forProposedRect: &rect, context: nil, hints: nil)
    }

}