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)
The switching of the location works
The moving of the player also works in case the player is plain Node2D.
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.
I verified that the player does get removed from the scene.
I tested with a dummy scene (which only contains KinematicBody2D as root node and a simple Sprite as a single child) instead of my actual more complex Player scene to make sure it's not related to any other code I might have in my Player scene. Node2D as root works, KinematicBody2D crashes. Must have been a fluke. Tested again and now both work, so there must be something different in my Player object.
I tried adding the Player node as a direct child of Location node (not having a YSort node in the middle) - nope, still crashes.
I tried setting the position/global_position of player before/after adding it to new scene - no difference.
I'm able to create new Player scene instance and add it to new location.
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.
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.
Related
I am adding a main menu to my game. The thing I am doing is adding them in a scene and then changing the scene to the game scene. However, my game has errors which belong to other scenes that do not have an instance in the existing scene. I get errors such as:
Invalid get index 'HasEntered' (on base: 'null instance').
My entire project is here: https://github.com/Ripple-Studios/Godot-Wild-Jam-36-Game-Ripple-Studios
I would appreciate if someone would help me.
Thanks,
I had a look at the linked code.
What is happening is that the practice of getting nodes of the parent has come back to bite you. I'm talking code that looks like this:
get_parent().get_node(...)
You have an scene (HospitalScene.tscn) instanced in your main scene (MainMenu.tscn), which has code similar to the shown above.
The particular error you refer to comes from code that looks like this:
func _on_Area2D_body_entered(body):
var HospitalPosition = get_parent().get_node("Hospital")
if HospitalPosition.HasEntered == true:
HospitalPosition.isInHospital = false
This code is firing at the start because the Area2D is overlapping an StaticBody.
The code is trying to get a sibling "Hospital" which does not exist in the scene tree. And thus HospitalPosition is null. And trying to access HospitalPosition.HasEntered when HospitalPosition is null results in the error you mention:
Invalid get index 'HasEntered' (on base: 'null instance').
The scene is trying to reach a node outside of itself. And there is no guarantee that the scene will be instanced where such node is available. Thus, in each and every case of get_parent().get_node(...) this could happen.
In fact, when running the game, I get four error that look like this (but with different paths):
E 0:00:01.494 get_node: (Node not found: "Hospital" (relative to "/root/CanvasLayer/ParentSprite/Control").)
<C++ Error> Condition "!node" is true. Returned: nullptr
<C++ Source> scene/main/node.cpp:1325 # get_node()
<Stack Trace> HospitalScene.gd:28 # _on_Area2D_body_entered()
You could use get_node_or_null instead of get_node and check for null.
You could also export NodePath variables instead of hard-coding the paths.
Better decoupling strategies than checking if instances are valid include:
Connect to the signal from outside the scene. It is a common pattern in Godot to call down the scene tree, and signal up the scene tree. See Node communication (the right way).
Connect all the signals through an Autoload (singleton). Which is another common pattern in Godot called a Signal Bus or Event Bus. See Best practices: Godot GDScript - Event Bus.
Lots of googling and I'm still not grasping what is probably a simple solution.
Scene: "Main". Contains a TileMap "Grid" with a script attached to it "Grid.gd".
Scene: "Player". Contains a KinematicBody2D "Player" with a script attached to it "Player.gd"
In Player.gd, I need to call a method in Grid.gd "_Calculate", pass it two variables, and have it return one variable.
var vNewPosition = Grid._Calculate(vPlayer, vInputDirection)
Error: The identifier "Grid" isn't declared in the current scope.
Obiously I need to reference the Grid.gd script somewhere to access it, but none of the many examples I have tried work.
Thanks in advance,
Josh
Given that
The Main scene has an instance of the Player scene
And
In Player.gd, I need to call a method in Grid.gd "_Calculate", pass it two variables, and have it return one variable.
I'll give you a few options.
The bad way
If Player knows the node path to Grid, it could use get_node to get it.
onready var _grid = get_node("../../grid")
Or something like that.
And then use it:
var vNewPosition = _grid._Calculate(vPlayer, vInputDirection)
This approach is, of course, not recommended. It will break if the node path is wrong.
The common way
Assuming Player does not know the node path (which is more likely), you can export a NodePath variable in Player.gd and use it to get the Grid:
exprort var grid_path:NodePath
onready var _grid = get_node(grid_path)
Then you need to set the Grid Path property in the Main scene to Grid.
This approach is better than the prior one, in that it does not depend on the path to Grid. However it still depends on a Grid being there. If Player makes no sense when there is no Grid, this approach is OK.
The good way
If Grid may or may not be there, and we want Player to work regardless, we can tweak the above approach:
exprort var grid_path:NodePath
onready var _grid = get_node_or_null(grid_path)
And remember to check if grid is null before using it:
if grid == null:
return # or whatever
var vNewPosition = grid._Calculate(vPlayer, vInputDirection)
Or like this:
var vNewPosition = grid._Calculate(vPlayer, vInputDirection) if grid != null else null
Which also allows us to specify a default value that vNewPosition will take when there is no grid (the null at the end of the line). And thus you can have the Player work when there is no Grid, and when there is it will use, and regardless of where (because Main tells it where it is).
This solution is not completely decoupled, because Player still knows grid is a thing that has _Calculate. Also we presume there is zero or one, not multiple. I can think of a way to approach that, but decoupling for the sake of decoupling is unnecessary. I'm calling this good enough for your use case. Yet, let me know if you want the over-engineered way.
I can't link SliceAndCoagulatorScene to the script to set its visible to false I've tried get_node, $res://...
extends Node2D
onready var main_scene = get_node(".")
onready var SliceAndCoagulatorScene = get_node("_________")
func _ready():
main_scene.visible = true
This is what I would like to put after :
SliceAndCoagulatorScene.visible = false
How could I do this, any help is appreciated
For clarity: A res:// path does not exist in the scene tree, it exists in the virtual file system. As such, you cannot access it from get_node. Because get_node works on the scene tree, thus you need to load and instantiate the scene in the scene tree first.
If you have added the scene to the scene tree in the editor, then it will load it and instantiate it for you, and there will be a path you can put in get_node... But it will not be a res:// path, because, again, a res:// path exists in the virtual file system.
You give res:// paths to load (or load_interactive, see Background loading, or change_scene), not to get_node.
Now, either you are trying to target a scene that is loaded or one that isn't.
If your other scene is not loaded, you need to load it (load or load_interactive) which gives you a PackedScene, instantiate it (instance) which gives you a Node. At which point you have a reference, go ahead an use it. You probably want to add to the scene tree (e.g. add_child).
For example, here we attach the new scene to the root (which may or may not be what you want, in particular in the face of changing scenes, but that is another topic):
func _ready():
var packed_scene = load("res://something.tscn")
var scene_node = packed_scene.instance()
var root = get_tree().get_root()
root.add_child(scene_node)
scene_node.visible = false # or whatever
I will suggest to use a PackedScene export:
export(PackedScene) var packed_scene
onready var scene_node = load(packed_scene).instance()
func _ready():
var root = get_tree().get_root()
root.add_child(scene_node)
scene_node.visible = false # or whatever
Then in the inspector panel you will see a new property "Packed Scene" (Godot auto capitalizes the name) where you can specify the scene from the file system. Plus, if you move scenes in the file system in the editor, the editor will update the path for you.
Note: you may or may not want to add them to get_tree().get_root(). Other options include adding it to get_tree().get_current_scene(), get_owner(), get_parent() and to self.
On the other hand, both your scenes are already loaded in the scene tree. In which case, there is a path from one node to the other, which you can put in get_node. If your target scene is not a child, you probably want to go up a few levels with ... However, I would advice against hard-coding such path.
Instead, you will get a lot of leverage of the following:
export(NodePath) var target_scene
onready var scene_node = get_node(target_scene)
Then in the inspector panel you will see a new property "Target Scene" where you can specify where in the scene tree the node you want to access is. Plus, if you move the nodes around in the scene tree in the editor, it will update the path for you.
Then you can do:
func _ready():
scene_node.visible = false # or whatever
Note: If you don't know if the scene is loaded. You might be interested in using find_node. Control also provide a get_node_or_null.
I am trying to get a dynamically instanced kinematicBody2D with an area 2D attached to handle mouse entered/exit inputs. I have created my area 2D with correct collision body, and have tested a similar collision body for detecting some area 2d's and this is working happily, however, the mouse detection is not triggering the function as it should.
I am unsure of why it does not appear to be detecting my mouse. I am assuming I have messed with the Masks incorrectly, and it is not on the same level, however looking at some of the documentation this is not suggested to be a problem.
I am unsure of what code to attach because it is not really coded at this point.
Any help would be appreciated.
To detect mouse events on an Area or KinematicBody, set input_pickable to true and connect to one or more of the provided signals.
KinematicBody2D and Area2D both inherit from CollisionObject2D, so they can both handle mouse input. This means you don't need to add an Area to your KinematicBody unless the area that detects clicks needs to be different than the area that detects collisions (e.g. only a small part of a larger object is clickable).
Here's how you could detect mouse events on a KinematicBody with some CollisionShape:
func _ready():
input_pickable = true
connect("mouse_entered", self, "_on_mouse_entered")
connect("mouse_entered", self, "_on_mouse_entered")
connect("input_event", self, "_on_input_event")
func _on_mouse_entered():
print("mouse entered")
func _on_mouse_exited():
print("mouse exited")
func _on_input_event(viewport, input_event, shape_idx):
var mouse_event = input_event as InputEventMouseButton
if mouse_event:
prints("Mouse button clicked:", mouse_event.button_index)
I am trying to create a topdown shooter with a player and a bullet on a separate scene. But whenever I run the game it says
Attempt to call function 'get_position' in base 'null instance' on a null instance.
BTW I am new to Godot.
The problem seems to be in this function:
const SPEED = 300
var bullet = preload("res://Mini-Scenes/Bullet.tscn")
func shoot():
var b = bullet.instance()
add_child(b)
b.set_position(position)
b.move_and_slide(Vector2(1, 0).rotated(rotation) * SPEED)
And I also don't think that I understand how instancing works,
so my questions are:
How does Instancing work?
What makes the above function fail?
Alright, in order:
Instancing is simple in principle. Godot takes the base Node of a scene and all its children, and copy-and-pastes them into memory. Then, when you add this Node as child to another in the scene, _ready is called, the Nodes begin to _process and _physics_process, as well as a few other things like receive events (as a Node must be within a SceneTree in order to interact with other nodes, and the most common way to add one to a tree is making it the child of another).
For more information, see the documentation on Instancing
The above function actually works flawlessly, I just created a new project in Godot 3.1.1 and duplicated your setup, no errors occur. The problem must be somewhere else in your code or your scene setup, and we'd need to see your full script and scene layout to determine the cause of the problem. If you update your question with that information, or shoot me a message on Discord (Mantissa#2558), I'll be able to fully answer your question.