Add mouse input interaction to GridMap

[rafallus]

Based on this proposal godotengine/godot-proposals#3818. input_event, mouse_entered and mouse_exited signals are implemented.
This can avoid the trouble found when raycasting on GridMap's shapes (see #46561).
With this implementation it becomes much easier to do things like this:

I include the project I used for testing.
GridMapTest.zip

Bugsquad edit: This closes godotengine/godot-proposals#3818.

[akien-mga]

I don't think having GridMap creep its way into something as core as Viewport will be acceptable.

I'm not sure how this should be done but this is probably not the way.

[rafallus]

Could a unhandled_input_picking signal from the viewport work? That way GridMap can connect to it and receive the information needed. If yes, should the signal be exposed to GDScript?

[akien-mga]

That might work, though I'm surprised that there wouldn't be an existing system that can be suitable for GridMap. It's not the only node / editor that handles picking and if other gizmos can do it, then GridMap should be able to do it too (just talking in principle - I'm not actually familiar with that code and might be wrong).

CC @JFonS @RandomShaper

[rafallus]

Well, that can certainly be done with the normal unhandled_input. But since the viewport is already checking for collisions I think that can be used and avoid repeating code. Also, the process_picking method (the one that takes care of collisions) is called inside physics_process of the SceneTree. If we want the input to also be processed in GridMap's physics_process, the inputs should be collected first and then processed. To me, that's a bit too much for something that is already implemented and can be reused.

[Zylann]

I would be interested in having a generic way to connect to this too in my plugins, because this issue is not specific to GridMap: godotengine/godot-proposals#3818 (comment)