CVDisplayLinkOutputCallback in Swift

CVDisplayLinkOutputCallback.swift

private func createDisplayLink() {
  CVDisplayLinkCreateWithActiveCGDisplays(&displayLink)
  guard let displayLink = displayLink else {
    return
  }
  
  let callback: CVDisplayLinkOutputCallback = { (_, _, _, _, _, userInfo) -> CVReturn in
    let myView = Unmanaged<MyView>.fromOpaque(COpaquePointer(userInfo)).takeUnretainedValue()
    dispatch_async(dispatch_get_main_queue()) {
      myView.update()
    }
    return kCVReturnSuccess
  }
    
  let userInfo = UnsafeMutablePointer<Void>(Unmanaged.passUnretained(self).toOpaque())
  CVDisplayLinkSetOutputCallback(displayLink, callback, userInfo)
  CVDisplayLinkStart(displayLink)
}

private func update() {
  // Do your view updates
}