How can it be determined that the user clicked on a layer?

You can use hit testing: to determine which layer was touched. Core Animation provides two methods for this:

1. hitTest(_:):

   • Checks whether a point is inside the bounds of the layer or any of its sublayers.
   • Returns the deepest sublayer (or the layer itself) containing the point.
   • Considers isHidden = true.

2. contains(_:):

   • Checks only if the point is inside the bounds of the layer itself.
   • Does not consider the hierarchy of sublayers.
   • Does not consider isHidden.

hitTest is usually used because it is more accurate for determining interactivity.

Example of using hitTest in a touch handler:

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    guard let touch = touches.first else { return }

    let locationInView = touch.location(in: view)

    // Convert the point from view coordinates to layer coordinates
    let locationInLayer = myLayer.convert(locationInView, from: view.layer)

    // Perform hit test
    if let hitLayer = myLayer.hitTest(locationInLayer) {
        if hitLayer === myLayer {
            // Touched exactly myLayer
            print("Touched myLayer")
        } else {
            // Touched a sublayer inside myLayer
            print("Touched a sublayer inside myLayer")
            // Identifying the sublayer may require additional checks
        }
    } else {
        // Touched outside myLayer and its sublayers
        print("Touched outside myLayer")
    }
}

Important points:

• Touch coordinates (location(in:)) are always relative to UIView. They need to be converted to layer coordinate system (convert(_, from:) or convert(_, to:)).
• The hitTest(_:) method works with points in the coordinate system of the calling layer (myLayer.hitTest(locationInLayer)).
• If the layer is invisible (alpha = 0 or isHidden = true), hitTest will return nil. contains will return true if the point is inside the bounds, ignoring visibility.
• For complex layer hierarchies, recursive search or checking the returned hitLayer may be necessary.