[PLEASE READ] Some Unity v6 games imcompatibility

[yukieiji]

Important

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Overview

Certain Unity v6(almost v6.3) games are currently incompatible with UE.
Due to various underlying technical complexities, these cannot be addressed simply as bugs within the UE core. A coordinated fix involving integration with Il2CppInerOps and Mono is required.
All the proposed fixes for these issues are complex and would significantly increase technical debt. While they are easy to merge, the long-term support and maintenance costs make them completely unacceptable.

Confirmed Incompatible Games

• My Dystopian Robot Girlfriend
• RUMBLE
• Polytoria
• skinface
• Eminence in Shadow - Master of Garden
• ATLYSS
• The Planet Crafter
• Rhythm Doctor
• MallRivals

Issues

System.MissingMethodException: Method not found: 'System.String UnityEngine.SceneManagement.Scene.GetNameInternal(Int32)'

Cause: This is due to the Screen handle being changed to a specialized type in recent Unity updates.

I have fixed the bug where internal APIs prone to breaking changes were being called directly. However, my analysis confirms that although an implicit conversion to int is defined, it is currently failing to trigger. Consequently, even the officially supported external APIs are non-functional.

Related Tickets

#105 , #102 , #100 , #95 , #94 , #85 , #81

AssetBundle.XXX can't work

Cause: Due to optimizations, the AssetBundle loading logic has been transitioned to the Span family. This change is not being handled correctly, leading to numerous reports specifically in Il2Cpp-based games. While a provisional workaround has been implemented, stable operation is not yet guaranteed.

Related Tickets

BepInEx/Il2CppInterop#202

#103 , #92 , #89 , #88 , #75

[Marioalexsan]

I'm not gonna claim my code solves every facet of Unity 6 since I didn't handle IL2CPP, but this is very much an issue in your approach with respect to the issues (or rather refusal in doing so, given that you closed multiple issues that were opened on this!)

Here's proof the Scene stuff can be fixed on Mono. This works just fine on ATLYSS with Unity 6 right now, but I don't mod IL2CPP games to be able to fix it for those ones:
AtlyssModding@7bed94a
AtlyssModding/UniverseLib@ec46128

However, my analysis confirms that although an implicit conversion to int is defined, it is currently failing to trigger. Consequently, even the officially supported external APIs are non-functional.

There is no such thing as "implicit" at Intermediate Language level, which is where your code fails right now on Unity 6. The implicit conversions that happen in C# land get converted to explicit "op_Implicit" method calls in IL land. You do not have those conversions provided to you by just calling the method through reflection. (although you could probably write a custom binder, perhaps.) Which is why you need to insert the conversion yourself if you want to be able to handle both Unity 6 and versions lower than it.

[yukieiji]

I'm not gonna claim my code solves every facet of Unity 6 since I didn't handle IL2CPP, but this is very much an issue in your approach with respect to the issues (or rather refusal in doing so, given that you closed multiple issues that were opened on this!)
Here's proof the Scene stuff can be fixed on Mono. This works just fine on ATLYSS with Unity 6 right now, but I don't mod IL2CPP games to be able to fix it for those ones:

I don’t think any of the proposed fixes currently on the table are the right solution (including the code you modified).
They’re all just stopgap measures, and for stopgap measures, they’re unnecessarily complex.
If you consider this approach negligent, then you should take over all UE development yourself.

[ninjaguardian]

Is the issue with fixes like that that they would be incompatible with pre-SceneHandle unity versions?

[yukieiji]

Is the issue with fixes like that that they would be incompatible with pre-SceneHandle unity versions?

No, because it doesn't seem likely that forward compatibility with ModLoaders like BepInEx and MelonLoader, as well as Unity, can be maintained.

Personally, I believe these issues should be addressed primarily on the ModLoader side.
If a temporary fix is to be implemented on the UE side, it should be limited to no more than about 20 lines of code; otherwise, it will make future fixes more difficult.

[Bamboy]

Can we confirm that all unity games will have access to Span and related types, considering it's still (somewhat) new and Unity really likes older .net versions? More specifically, is it possible these types are being stripped at compile time by some compilers or dev tools by the game authors?

I've been trying to make a mod for Megabonk (Unity 2023.2, IL2CPP) for the past few days under linux/wine and I keep running into this issue, specifically an output log that resembles #75 but for ReadOnlySpan:

[07:25:09.670] [UnityExplorer] [UniverseLib] 	 IL2CPP method has no corresponding pointer, aborting patch of UnityEngine.AssetBundle.UnloadAllAssetBundles
[07:25:09.679] [DEBUG] [MelonAssemblyResolver] Attempting to find Il2CppSystem.Private.CoreLib
...
[07:25:09.697] [DEBUG] [MelonAssemblyResolver] Failed to find Il2CppSystem.Private.CoreLib in any of the known search directories

...

Il2CppInterop.Runtime.ObjectCollectedException: Object was garbage collected in IL2CPP domain
   at Il2CppInterop.Runtime.InteropTypes.Il2CppObjectBase.get_Pointer() in /home/runner/work/Il2CppInterop/Il2CppInterop/Il2CppInterop.Runtime/InteropTypes/Il2CppObjectBase.cs:line 32
   at Il2CppSystem.Span`1..ctor(Il2CppArrayBase`1 array)
   at UnityEngine.AssetBundle.LoadFromMemory_Internal(Il2CppStructArray`1 binary, UInt32 crc)
   at (il2cpp -> managed) LoadFromMemory_Internal(IntPtr , UInt32 , Il2CppMethodInfo* )
...
System.MissingMethodException: Method not found: '!0 ByRef Il2CppSystem.ReadOnlySpan`1.GetPinnableReference()'.
   at UnityEngine.AssetBundle.LoadAsset_Internal(String name, Type type)
   at (il2cpp -> managed) LoadAsset_Internal(IntPtr , IntPtr , IntPtr , Il2CppMethodInfo* )
[07:25:09.812] [Il2CppInterop] Exception in IL2CPP-to-Managed trampoline, not passing it to il2cpp: System.NullReferenceException: Object reference not set to an instance of an object.
   at UniverseLib.UI.UniversalUI.LoadBundle() in D:\a\UnityExplorer\UnityExplorer\UniverseLib\src\UI\UniversalUI.cs:line 233
   at UniverseLib.UI.UniversalUI.Init() in D:\a\UnityExplorer\UnityExplorer\UniverseLib\src\UI\UniversalUI.cs:line 105
   at UniverseLib.Universe.SetupCoroutine()+MoveNext() in D:\a\UnityExplorer\UnityExplorer\UniverseLib\src\Universe.cs:line 134
   at Trampoline_ByteThisUniverseLib.Runtime.Il2Cpp.Il2CppManagedEnumeratorMoveNext(IntPtr , Il2CppMethodInfo* )

My log contains similar messages/errors I've seen reported by other users. Full MelonLoader log
But, I just haven't been able to completely resolve if the issue is with MelonLoader, my linux setup, UnityExplorer, or etc.

[yukieiji]

Can we confirm that all unity games will have access to Span and related types, considering it's still (somewhat) new and Unity really likes older .net versions? More specifically, is it possible these types are being stripped at compile time by some compilers or dev tools by the game authors?

This also issue under the second issue( #103 ).
Since this doesn't occur in older versions of Unity, types such as Span may not exist depending on the Unity version.

[pelijot]

Can confirm that A Webbing Journey has the same issue (Method not found)

[Javialonqv]

Hi, excuse my ignorance, but I'm new here checking the UE source code, I faced the same problem with Unity 6 about the new Scene structure (replaced int for SceneHandle), I understand that you don't wanna update any old DLLs in the project because of compatibility with older versions, however, the only solution so far SEEMS to be using reflection to call the new API at runtime, UE already seems to be using a lot of it so I don't quite understand why you don't want that approach.