hitTest for MTKView

I am trying to make a metal window receive pointer events at a certain part only. I have extended the MTKView:

class MainView: MTKView {
  override func hitTest(_ point: NSPoint) -> NSView? {
    print(point)
    return nil
  }
}

The MainView instance is the only view in the window. The hitTest() Function is get called (I can see it in the logs) but I can't click through the transparent part (or any part) of the window. How can I make the windows behind receive the pointer events?