Making a window controller with a popover appearance (which didn't go into code, but might be useful in the future)

NSPopoverDelegate.swift

func detachableWindow(for popover: NSPopover) -> NSWindow? {
    let windowController = NSStoryboard.main?.instantiateController(withIdentifier: .replyWindowController) as! NSWindowController
    let replyPopupViewController = windowController.contentViewController as! ReplyPopoverViewController
    replyPopupViewController.comment = comment
    let window = windowController.window!
    window.setContentSize(popover.contentSize)
    window.isMovableByWindowBackground = true
    let visualEffectView = window.contentView as! NSVisualEffectView
    visualEffectView.state = .active
    visualEffectView.material = .popover
    let maskImage = NSImage(size: NSSize(width: 16, height: 16), flipped: false) { rect in
        let bezierPath = NSBezierPath(roundedRect: rect, xRadius: 8, yRadius: 8)
        NSColor.black.set()
        bezierPath.fill()
        return true
    }
    maskImage.capInsets = NSEdgeInsets(top: 8, left: 8, bottom: 8, right: 8)
    visualEffectView.maskImage = maskImage
    return window
}