CODEWITHSUNDEEP
godotgdscript
Rene Saarsoo
Rene Saarsoo

Reputation: 13917

Godot: How to move KinematicBody2D node from one scene to another

I want to move my Player node (KinematicBody2D) from one scene to another. My code successfully moves Node2D node, but fails with KinematicBody2D node.

I have two Location scenes (inheriting from base Location scene) with the following structure:

FirstLocation (inherits Location)
  - YSort
    - Player

In the base Location scene I have two methods:

func add_player(player: Player):
    get_node("YSort").add_child(player)

func remove_player() -> Player:
    var player = get_node("YSort/Player")
    get_node("YSort").remove_child(player)
    return player

In GameWorld scene I store the possible locations inside a dictionary and the moving of the player happens inside change_location() function:

onready var _locations = {
    Location.FOO: $CurrentLocation,
    Location.BAR: load("res://locations/Bar.tscn").instance(),
}

onready var _current_location = $CurrentLocation

func change_location(location: int):
    var player = _current_location.remove_player()

    remove_child(_current_location)
    _current_location = _locations[location]
    add_child(_current_location)

    _current_location.add_player(player)

But when Player is KinematicBody2D then the game simply crashes, giving me no hint as to what's causing the problem.

The code works without crashing when I comment out the last line:

    _current_location.add_player(player)

...but of course then the player simply doesn't get added to the other scene.

What might it be in KinematicBody2D that prevents me from moving it from scene to scene?

Found a solution, but I don't know why it works.

I was performing the location change as a response to Area2D.body_entered signal. I triggered my own signal "location_change" and then called the change_location() function in another part of the code in response to it.

Adding a tiny timeout (0.00000001 seconds) before doing the location change solved the issue. However I have no idea why, and I'm pretty sure adding timeouts is not a proper way to solve this problem.

Upvotes: 1

Views: 923

Answers (1)

Theraot
Theraot

Reputation: 40295

I'm having trouble visualizing the situation. However, given that the problem happens when removing and adding a physics body, and that "body_entered" was involved, and that the solution you found was adding a time out…

Sounds like the issue was removing the physics body while Godot was still resolving physics response. And then the solution was to wait until the next frame.

You could wait until the next graphics frame with this:

yield(get_tree(), "idle_frame")

Or until the next physics frame with this:

yield(get_tree(), "physics_frame")

Which would be better than some arbitrary small timeout.

Alternatively, you could also make the signal connection deferred.

If you are connecting from the UI, there will be an "advanced" toggle in the "Connect a Signal to a Method" dialog. Enabling "advanced" toggle will reveal some extra including making the connection deferred.

If you are connecting form code, you can accomplish the same thing by passing the CONNECT_DEFERRED flag.

Upvotes: 1

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