(Case 956356) Creating scene outputs different .unity file always

(Programmatically) creating a scene with the same content, produces an .unity file with different content always. It seems the GameObject's inside the scene file are stored randomly.

The provided example creates a new scene and places a few prefabs at hard-coded positions. It's always the same. However, comparing the produced .unity file with a diff tool (such as TortoiseMerge), shows the scene file is different always.

This causes version control issues. Most likely different asset bundles as well, even though the actual scene is identical.

Spoiler: C# Source Code

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEditor;
5.  
6. class CreateSceneTest
7. {
8.     [MenuItem("Test/Create Scene A")]
9.     static void DoMenuItem()
10.     {
11.         // create a new scene
12.         var scene = UnityEditor.SceneManagement.EditorSceneManager.NewScene(UnityEditor.SceneManagement.NewSceneSetup.EmptyScene);
13.  
14.         // create a floor place
15.         var floor = (GameObject)PrefabUtility.InstantiatePrefab(AssetDatabase.LoadAssetAtPath<GameObject>("Assets/Art/Floor.prefab"));
16.         floor.transform.SetPositionAndRotation(Vector3.zero, Quaternion.identity);
17.         floor.transform.SetAsLastSibling();
18.  
19.         // create a few prefabs
20.         foreach (var pos in new Vector3[] {
21.             new Vector3(5, 0, 0),
22.             new Vector3(0, 5, 0),
23.             new Vector3(0, 0, 5),})
24.         {
25.             var cube = (GameObject)PrefabUtility.InstantiatePrefab(AssetDatabase.LoadAssetAtPath<GameObject>("Assets/Art/Cube.prefab"));
26.             cube.transform.SetPositionAndRotation(pos, Quaternion.identity);
27.             cube.transform.SetAsLastSibling();
28.         }
29.  
30.         // save scene
31.         UnityEditor.SceneManagement.EditorSceneManager.MarkSceneDirty(scene);
32.         UnityEditor.SceneManagement.EditorSceneManager.SaveScene(scene, "Assets/Scenes/Scene A.unity");
33.     }
34. }
35.  

Reproduce

• Open user attached project
• Press Mainmenu/Test/Create Scene A
• Duplicate generated "Scenes/Scene A.unity" and rename it to "Backup"
• Press Mainmenu/Test/Create Scene A
• Compare "Scenes/Scene A.unity" and rename it to "Scenes/Backup" with a diff tool

Observe the file content is different.


Expected
The produced file should be the same. If the input is identical, the output should be identical as well.

 

QA was able to reproduce the issue and it's now added to the public Issue Tracker
https://issuetracker.unity3d.com/issues/creating-identical-scene-always-outputs-different-unity-file

 

Which is exactly the problem we have.

We use an external application (not Unity) to create levels. It's a level editor that is optimized for the kind of content we need to produce. We save the level created by that external editor to the Unity project and have custom code that converts this file to an Unity scene.

However, every time we convert the same level (input), the Unity scene file (output) is completely different.

How do I get "deterministic scene files"? If there is a solution to this at all.

 

I see, thanks for your help!