Get closest CollisionObject2D in tree order for overlapping CollisionObject2Ds

[jkvastad]

In a game with 2D elements, it is a very common action to click something which is rendered "closest" or "topmost" to the user, in analogy with render order for CanvasItem.

Imagine multiple overlapping Area2Ds. Perhaps representing a deck of cards. We can raycast a point using intersect_point to get all the overlapping cards - but how to get the top card?

I feel the engine should make such a simple task trivial, yet I run into massive headaches. Do I really need to Z-index each and every 2D object? Why can't I get the current tree order of a CanvasItem? In short - I just want to click the thing I see on the screen.

On a related note for context, see disussion 8965, issue 1058 and a forum post I made on the topic.

[jkvastad]

Turns out is possible to achieve this for Node2D using Node.is_greater_than, as outlined in this forum post. Yay!

As Mrcdk writes there, do e.g.

var intersections = direct_space.intersect_point(query)
		if intersections:
			intersections.sort_custom(func(a, b):
				var obj_a = a.collider
				var obj_b = b.collider
				return obj_a.is_greater_than(obj_b)
			)