Cyclical references killed my entire project

A.R · March 24, 2024, 10:19pm

So Godot does not like circular references. If your main scene is part of a circular reference it corrupts the project and makes the scene un-openable.
The Godot dev’s say this is not a bug. But it sure feels like one.

Don’t try and test your scene by having Scene A load Scene B which then loads Scene A.
[4.0 RC 1] Can’t switch to packed scene that was started in using change_scene_to_packed #72921**

github.com/godotengine/godot

[4.0 RC 1] Can't switch to packed scene that was started in using change_scene_to_packed

opened 08:43PM - 08 Feb 23 UTC

closed 01:29PM - 28 Feb 23 UTC

KittenAqua

archived

### Godot version 4.0 RC 1 ### System information Windows 10 ### Iss…ue description I cannot switch back to the packed scene that I start in. Hard to describe, so see the minimal reproduction project if my description is difficult to follow. I have two scenes, SceneA and SceneB, that just switch between eachother repeatedly by preloading and using `change_scene_to_packed`. - SceneA has a button that switches to SceneB with `get_tree().change_scene_to_packed(scene_b)` - SceneB has a button that switches to SceneA with `get_tree().change_scene_to_packed(scene_a)` But I can't seem to switch back to whatever scene I start in. - If I start in SceneA and switch to SceneB, I can't switch back to SceneA (`ERR_CANT_CREATE`) - If I start in SceneB and switch to SceneA, I can't switch back to SceneB. I tried adding a third scene, SceneC, that switches to SceneA. - If I start in SceneC, I can switch back and forth between SceneA and SceneB endlessly, so the conclusion is that I can't switch back to whatever scene I start in. This error is specific to packed scenes, but it doesn't require `change_scene_to_packed` specifically. If I use `change_scene_to_file` instead, there are no errors. However, if I use `change_scene_to_file` AND preload the packed scenes (even if I'm not using them), it will error. ### Steps to reproduce Open the minimal reproduction project. SCENE A FAILURE: - Run SceneA. - Click the button. It should switch to SceneB. - Now click the button in SceneB. It will fail to switch to SceneA and print the error code to the console (error code 20 - ERR_CANT_CREATE). SCENE B FAILURE: - Run SceneB. - Click the button. It should switch to SceneA. - Now click the button in SceneA. It will fail to switch to SceneB and print the error code to the console (error code 20 - ERR_CANT_CREATE). SCENE C SUCCESS: - Run SceneC. - Click the button. It should switch to SceneA. - Now click the button in SceneA. It should take you to SceneB. - Now click the button in SceneB. It should take you back to SceneA. Since we never return to the scene we started in, there are no errors. ### Minimal reproduction project [SceneswitchTest.zip](https://github.com/godotengine/godot/files/10689710/SceneswitchTest.zip)

Trying to manually load new scenes to toggle back and forth between two scenes fails #83079**

github.com/godotengine/godot

Trying to manually load new scenes to toggle back and forth between two scenes fails

opened 12:22AM - 10 Oct 23 UTC

thorbrian

bug discussion topic:core topic:gdscript

### Godot version v4.1.1.stable.mono.official [bd6af8e0e] ### System infor…mation v4.1.1.stable.mono.official [bd6af8e0e] ### Issue description I tried to make two menu scenes, where I could go from one scene to another and back (a "MainMenu" that loads the "Level" and the "Level" can return back to the "MainMenu") I tried to use manual scene switching, where the new packed scenes are instantiated and added, and the old scene is removed (was doing this because I was hoping to eventually make the old scene animate out while the new scene is animating in) I tried to make the references to the packed scenes be by a packed scene reference (@export'd var of type PackedScene) editable in the editor (I did this so that I could, at some point, move around my files and have the references still be connected) When I did that, when the "Level" scene got loaded from the "MainMenu", the instantiated level lost it's assigned reference to the "MainMenu", so it couldn't return to main menu. If I make the "Level" the main scene, then it can load "MainMenu" using it's reference, but "MainMenu" then loses it's reference So I tried doing it instead with hardcoded paths to the PackedScenes in preloads, and then when I toggle back and forth a few times, it fails with some kind of circular reference error Finally, if I try to reopen the project, for some reason the editor claims Level.tscn is invalid/corrupt, when it is not. I can still run everything (with the same bad behavior) it's just the editor refuses to edit Level.tscn So the 3 problems are: 1. script vars of "@export var target_scene : PackedScene" are lost when I "target_scene.instantiate()" a PackedScene reference which itself has one of these vars 2. Going back and forth between scenes with scripts with have "var preloadedScene : PackedScene = preload("path")" references to each other eventually errors out with a circular reference error 3. Having two scenes with scripts with "@export var exportedMenu : PackedScene" where assigned to each other makes one (or both) of them considered invalid by the editor, on re-opening the project ### Steps to reproduce Open the attached project. Notice how it claims Level.tscn is invalid, but the file format is fine Run the project, which takes you to the main menu. Click the top button to go to the Level scene (which loads fine now, despite the editor saying it's invalid), and now inspect the scene remote'ly and see that it doesn't have the reference to MainMenu.tscn in it's "exportedMenu" variable, despite the packed scene file having the reference, so the top button to return to the main menu doesn't work Run the project again, which takes you to the main menu. Use the bottom buttons to go back and forth between MainMenu and Level, and notice after a few times, it fails with an error about a circular reference ### Minimal reproduction project [SceneToggleErrors.zip](https://github.com/godotengine/godot/files/12851372/SceneToggleErrors.zip)

A better method is described in this article.

CoreyKnecht · March 24, 2024, 10:29pm

Probably considered an unhandled exception more than a bug. Thanks for posting this =)

Fortunately, I don’t think your project is sunk for good. .tscn is short for “text-based scene;” if Godot won’t open your scene to let you fix the error, open the file in Notepad or something and you can comment/fix the offending lines there.

Hopefully you already knew about this and your own project is actually fine now, but if this note helps other people too, even better.

A.R · March 26, 2024, 1:55pm

@CoreyKnecht
Thanks for taking the time to explain this - much appreciated. It was not mentioned in the posts I linked, or in any of the documentation I read. I hope this helps others in the future.

@GameDevTV - if you are updating this course. Please consider adding a note about cyclical references preventing Godot from starting a project would be valuable. This error caused me to delete my project because I didn’t know how to fix it, causing me to lose 2 weeks of effort and motivation to complete the course.

CoreyKnecht · March 26, 2024, 3:24pm

Ohhhh man. That’s brutal. I hope you come back to it sometime soon, as it’s a solid course that you had some awful luck with (I’m pretty sure it was Kaan who explains the text-based scene thing - either him, or Bram in the 3D course. Maybe both). If you run into critical problems like that again, don’t be afraid to leverage the community either; there are people here who are more than happy to help you succeed =)

CoreyKnecht · March 26, 2024, 3:32pm

I just thought of something; these days, there are some pretty sophisticated ways to recover lost files. If you’ll pardon the expression, you have nothing to lose at this point; why not have a look through this and see if there’s anything that might help you recover the project:

And if you’re not on Windows, more relevant results are a search away.

A.R · March 27, 2024, 5:24am

Thanks BH67, I did recover the files, but editing the scene files did not work. Just resulted in parsing errors. This is a known problem in Godot, hence the reason I posted links to the Godot Github and to a work around using a main background scene that manages smaller scenes.

Yes, you are right, the GameDevTV courses are quite good. I appreciate the effort that has gone into them.

Thanks for the assistance.

A.R · March 27, 2024, 4:27pm

@CoreyKnecht - thanks for the insight. I got it to work.
For those who follow, I ended up doing the following steps for each scene in my project, try the scene (failed), and edit it in notepad++, try again. (I did not have to close Godot)

Cyclical scenes - debugging…

The load_steps parameter is equal to the total amount of resources (internal and external) plus one (for the file itself). If the file has no resources, load_steps is omitted.
[gd_scene load_steps=9 format=3 uid=“uid://dvw6o6awi5qa8”]
Find the offending scene and note the UID number
… id=“2_3k727”
Delete all instances of this UID (delete the * lines below)

[ext_resource type=“PackedScene” uid=“uid://dassgucjmy1v5” path=“res://Levels/levelC.tscn” id=“2_3k727”]
…
[node name=“LevelA” type=“Node2D”]
script = ExtResource(“1_7708q”)
next_level = ExtResource(“2_3k727”)

Reduce the load_steps by the number of resources deleted (1 in this case)
[gd_scene load_steps=8 format=3 uid=“uid://dvw6o6awi5qa8”]

CoreyKnecht · March 27, 2024, 4:50pm

th-4225872452
Congratulations! That’s fantastic! ^v^

Definitely bookmarking this in case I ever encounter corrupted files or whatnot.