Overlap test for NSView with tracking areas

NSViewOverlapTest.swift

import AppKit

extension NSView
{

    /// Checks if view overlaps with other views above it at specified **window** location.

    func overlapTest(_ point: NSPoint) -> Bool {

        // Perform hit test to get the view under mouse. Because it can be a view within
        // our tested view we should also check superviews. There might also be views that
        // overlap, but are not interactive, in which case for this to work as expected 
        // they must correctly implement hit test. 

        var view: NSView? = self.window?.contentView?.hitTest(point)
        while view != nil && view !== self { view = view?.superview }
        return view !== self
    }
}

/// This can be used as a base for non-interactive views, which also works with interface builder.

@IBDesignable class View: NSView
{
    @IBInspectable var ignoresMouseEvents: Bool = false

    override func hitTest(_ point: NSPoint) -> NSView? {
        return self.ignoresMouseEvents ? nil : super.hitTest(point)
    }
}

/// Custom view with tracking area…

@IBDesignable class MyView: NSView
{

    // …

    override func mouseEntered(with event: NSEvent) {
        guard !self.overlapTest(event.locationInWindow) else { return }
        // Good to go!
    }

    // …

}