Unload scene specific resources on demand

[ViktorVovk]

This is an implementation of functionality for unloading all resources from the scene we are leaving. For example, we have several scenes (Preloader, postPreloader) that contain a significant number of resources such as images, audio, spine animations, atlases, JSON files, and so on. After these scenes have been loaded, once we transition to the so-called main scene, we want to remove (unload) all resources from the scenes that we do not expect to return to during the game’s runtime.

Plan for implementing the unloading of scene-specific resources on the GDevelop side:

1. An additional boolean parameter needs to be added to the "change scene" action. Enabling this parameter will indicate that all resources specific to the scene being exited should be unloaded. It is assumed that we will not return to this scene during the game’s runtime.

2. During the execution of the "change scene" action, the _destroy method is eventually called on the scene object (in runtimescene.ts). At that point, the resource cleanup method disposeScene—implemented in the ResourceLoader class—is invoked.

3. The disposeScene method accepts the scene name as a parameter and creates a Map where the keys are resource types (ResourceKind) and the values are arrays of ResourceData.

4. In the ResourceLoader class, there is a field _resourceManagersMap where the keys are resource types (ResourceKind) and the values are resource managers. This makes it easy to correlate this map with the map of resources grouped by type since they share the same keys.

5. In each resource manager class, a method disposeByResourcesList has been implemented, which takes an array of resources that need to be cleared. This method performs the cleanup of the resources in the provided list.

[4ian]

There is already a loading screen that is shown if a scene is not yet ready. We could probably rely on this instead of adding a special case? I.e: calling replace should call push that will display a loading screen if needed.

[ViktorVovk]

refactored

[4ian]

Hi @ViktorVovk!
Main feedback is that we think the parameter to choose if a scene resources should be unloaded when the scene is left should be a property of the scene, instead of being a parameter of the action.
I.e: something that would be stored on the scene (in Layout.h, and serialized into the JSON, so you could read it ).

(we could imagine an action to change this at runtime, but in most cases it could be something that never changes).

The unloading algorithm could unload resources that are neither from a living scene (including the next one) nor a scene with the "unload" property disabled.

Let's discuss what this would imply and how this would impact the algorithm that unloads resources :)

[ViktorVovk]

Hi @4ian.
Thank you for taking the time to review this PR.
I agree with your comment regarding where the need to unload resources from the scene we’re leaving should be specified.
I’ve done some refactoring and moved this parameter into the scene’s properties.
By default, this parameter is set to false.

I would really appreciate it if you could take another look at this PR.
Best regards.

[D8H]

It's going in the right direction, thanks! I've added a few more comments.

[D8H]

bool UnloadSceneAssets() sounds as a method that actually unloads the assets.
What do you think about shouldUnloadAssetsWhenUnloaded?

Suggested change

	bool unloadSceneAssets = false; ///< True to unload scene assets after exit scene
	bool shouldUnloadAssetsWhenUnloaded = false; ///< True to unload scene assets after exit scene

[ViktorVovk]

Hi. Thanks for you review. I totally agree with you on that

[ViktorVovk]

Renamed!

[D8H]

This method is similar to gdjs.RuntimeGame.loadSceneAssets.
Did you face any issue using loadSceneAssets?

[ViktorVovk]

To be honest, I tried to understand and use the existing API, specifically RuntimeGame.loadSceneAssets. However, when I used it and then returned to a previously unloaded scene, the resources for that scene were not loaded again. Although the methods RuntimeGame.loadSceneAssets and RuntimeGame.loadSceneAssetsBySceneName seem quite similar, I assumed they perform different tasks, as they invoke different methods in the ResourceLoader.

RuntimeGame.loadSceneAssets calls this._resourcesLoader.loadAndProcessSceneResources, which in turn calls ResourceLoader.loadSceneResources. From my understanding, this method does not actually load the resources but rather is intended for scenarios when switching to a scene whose resources are not yet loaded, but already queued for loading.

In contrast, RuntimeGame.loadSceneAssetsBySceneName invokes this._resourcesLoader.loadSceneResourcesBySceneName, which explicitly loads resources of a previously unloaded scene.

As an external developer, and not fully immersed in the entire context of the project, I tried to alter or modify the existing codebase as minimally as possible, just to avoid breaking any existing functionality that I might not be aware of. I would greatly appreciate your help in understanding why I couldn’t successfully use RuntimeGame.loadSceneAssets. Perhaps there is something I overlooked.