ELI5 multiple / additive scenes..

[DrMeatball]

I thought I understood how / when to use additive scenes but I’m having trouble implementing which makes me think I don’t understand after all.

Every time I restart Unity, I lose all of my added scenes from my main Game scene. Why?

I have been using Additive Scenes to make my organization and project management better. I’ve been doing everything in separate scenes (lighting, logic, character / player, enemies, levels, puzzles, etc etc) for my world building and then adding them all to my main Game scene. Is this wrong?

I’ve already gone through this… Unity - Manual: Work with multiple scenes in Unity (unity3d.com)… really doesn’t tell my much of anything useful.

[arkano22]

@DrMeatball

I have been using Additive Scenes to make my organization and project management better. I’ve been doing everything in separate scenes (lighting, logic, character / player, enemies, levels, puzzles, etc etc) for my world building and then adding them all to my main Game scene. Is this wrong?

You can’t add scenes to the main Game scene (or any other scene, for that matter). There’s no such thing as scene nesting in Unity, so this doesn’t make any sense.

Each scene is still completely independent from each other. You can load and edit multiple scenes at the same time in the editor, but that’s all. So when you restart the editor, only one scene is opened.

Additive scenes are meant to be loaded at runtime. You edit your scenes in the editor, then you load them all additively using LoadSceneMode.Additive. You should prepare a LightingScene, a LogicScene, a EnemiesScene, etc. then load them all at runtime when needed.

From the manual:
https://docs.unity3d.com/2020.1/Documentation/Manual/MultiSceneEditing.html

To avoid having to set up your hierarchy every time you restart unity or to make it easy to store different setups you can use EditorSceneManager.GetSceneManagerSetup to get a list of SceneSetup objects which describes the current setup. You can then serialize these into a ScriptableObject or something else along with any other information you might want to store about your scene setup. To restore the hierarchy simply recreate the list of SceneSetups and use EditorSceneManager.RestoreSceneManagerSetup.

At runtime to get the list of loaded scenes simply get sceneCount and iterate over the scenes using GetSceneAt.

You can get the scene a GameObject belongs to through GameObject.scene and you can move a GameObject to the root of a scene using SceneManager.MoveGameObjectToScene.

It is recommended to avoid using DontDestroyOnLoad to persist manager GameObjects that you want to survive across scene loads. Instead, create a manager scene that has all your managers and use SceneManager.LoadScene(, LoadSceneMode.Additive) and SceneManager.UnloadScene to manage your game progress.

[Kurt-Dekker]

Here’s a bit more reading on the subject… it can take a while to sorta wrap your head around:

Additive scene loading is one possible solution:

Right way for performance, divide scene?

I always favor breaking the scenes up and loading additively. reduces overall memory consumption lets multiple team members trample on each other less often ensures clean "reset" of all objects in a fresh loaded scene I'm working on a game now where we each have our own "content" level, the level we're working on. the content scene has all the lighting baked in. Just press play and that level has one script that additively loads: music scene (just an audiosource on autoplay) the p…

Right way for performance, divide scene?

Glad you asked… going this route definitely requires slightly-higher awareness of what scene is what. In no particular order, responding to you questions, When the game or level is over, I try to go to a fresh “end level” scene (not additively!) and clear everything else out (except overall ongoing game manager obviously, as a singleton) when the game gets paused I stop time and bring up a pause scene that sorts above all else, then unload it and restart the time. OR if you quit, I just …

Problem with canvas & UI prefabs

There are underlying reasons this happened and you can track it down by examining everything about each scene's canvas setup and scaling that are different from the other. But keep in mind it might not be super-easily to address it in the general case, especially if you start partitioning your UI into chunks. An alternate workflow is to put chunks of your UI into separate scenes and then load those scenes additively. For instance you might have the following scenes, all loaded additively: …

A multi-scene loader thingy:

Unity additive scene loading example - Pastebin.com

My typical Scene Loader:

https://gist.github.com/kurtdekker/862da3bc22ee13aff61a7606ece6fdd3

Other notes on additive scene loading:

Removing Duplicates on Load Scene

Why not remove the player from ALL your scenes, put him in his own separate scene, then load scenes additively? That way you don’t even need a Player prefab at all, just have a Player scene and load him additively. I tend to break up all my games into partial scenes, all additively loaded by the game manager: UI player enemy manager other stuff? and then finally I load the content scene. The first batch of screens all have scripts that do nothing until the content scene appears and they kn…

Timing of scene loading:

Function called from preloader script doesn't change parent of gameobject (in the second scene)

If line 8 relies on something being present from the scene load in line 7 (in GameController), it won't be: scenes are loaded at the end of frame and would never be available until the next frame, at the very earliest. You can trivially make void Start() into a coroutine by declaring it to return an IEnumerator, then put a while loop (with a yield return null; in it!!!) to wait until the scene loads and you find the "Trains" object, then proceed. Obviously you would need to interlock other t…

Also, if something exists only in one scene, DO NOT MAKE A PREFAB out of it. It’s a waste of time and needlessly splits your work between two files, the prefab and the scene, leading to many possible errors and edge cases.

Two similar examples of checking if everything is ready to go:

Daily Events and content changes

I think multiple scenes are definitely worth chasing. You need to make everything in your game tolerant of perhaps not having stuff ready at the same time, and you have to track things that you need only ONE of: Camera (Main) Audio Listener EventSystem I like to put all of those in the BASE scene if possible, then load other scenes like UI and pause and the level itself, etc. You have to sort of figure out which works for you. You can actually make Start() be a coroutine too, such as lookin…

Unit scripts calling Start function before other scripts

Indeed. I like to use a lot of additively-loaded scenes, so I tend to code my individual item controllers (including the player controller) so that they are happy to wait around if other stuff isn’t ready yet. You can make Start() into a coroutine, which is a super-easy way to get this kind of lazy-sloppy startup that is extremely tolerant of late loading and uneven loading. // typical base framework for all entities bool ready; IEnumerator Start () { // don't proceed unt…

[flashframe]

Just to add - you CAN save and load “Scene Setups” to make working with multi-scene workflow more tolerable in the editor. (e.g. if you want some scenes to always be opened together when working in the editor). You just have to write some custom code to get it working.

Unity - Scripting API: SceneSetup

Unity - Scripting API:...

You can store SceneSetups in scriptable objects in your project:

public class SceneCollection : ScriptableObject
{
    public SceneSetup[] setup;

    public void SaveSetup()
    {
        setup = EditorSceneManager.GetSceneManagerSetup();
    }

    public void LoadSetup()
    {
        if (EditorSceneManager.SaveCurrentModifiedScenesIfUserWantsTo())
        {
            EditorSceneManager.RestoreSceneManagerSetup(setup);
        }
    }
}

I have a custom editor window that is registered for the “sceneOpened” event in the EditorSceneManager to auto restore a setup when a scene is opened in the editor

Unity - Scripting API: SceneManagement.EditorSceneManager.sceneOpened

private string lastActiveScene;

private void OnSceneOpened(Scene scene, OpenSceneMode mode)
{
    if (mode == OpenSceneMode.Additive) return;
    if (SceneManager.GetActiveScene() != scene) return;
    if (string.Equals(lastActiveScene, scene.path)) return;

    lastActiveScene = scene.path;

    if (sceneCollections == null || sceneCollections.Count == 0) return;

    foreach (SceneCollection sc in sceneCollections)
    {
        if (sc.setup == null || sc.setup.Length <= 0) continue;

        foreach (SceneSetup setup in sc.setup)
        {
            if (!setup.isActive) continue;
            if (string.Equals(setup.path, scene.path))
            {
                Debug.Log("Restoring" + sc.name + " Scene Setup", sc);
                sc.LoadSetup();
                return;
            }
        }
    }
}