World/Udon Bugs & Feature Requests

When a player joins a world a FieldChangeCallback is sometimes called before Start(). I am using a variable set in Start() inside a FieldChangeCallback and due to Start() not being called first the script dies in the FieldChangeCallback with "Object reference not set to an instance of an object". When it happens seems to be completely random; it happened to my friend for the first time today when he joined me and just now in my local testing it took me 10 and 50 times of rejoining the world for this to occur. So far I have only seen it happen for a non-owner joining the world. This code has remained unchanged since 2021 and only recently this year I have started seeing this issue.

When calling SetLoops on a VRCTweenHandle created from VRCTween.DelayedCall, it is expected that the tween periodically invokes its callback according to the specified duration and loop count. In actuality however the tween invokes its callback once then terminates, as if SetLoops wasn't called at all.

Environment: Unity version: 2022.3.22f1 VRChat SDK Worlds: 3.10.3 VRChat SDK Base: 3.10.3 UdonSharp included with SDK Project uses Prefab Mode / PrefabStage with UdonSharpBehaviour components YamaPlayer package present: net.kwxxx.yama-stream 1.5.18 Observed: When opening or editing prefabs containing UdonSharpBehaviour components in Prefab Mode, Unity logs repeated ArgumentNullException errors from OdinSerializer UnitySerializationUtility. Error: ArgumentNullException: Value cannot be null. Parameter name: unityObject VRC.Udon.Serialization.OdinSerializer.UnitySerializationUtility.SerializeUnityObject(...) UdonSharp.UdonSharpBehaviour.UnityEngine.ISerializationCallbackReceiver.OnBeforeSerialize() and similarly: UnitySerializationUtility.DeserializeUnityObject(...) UdonSharp.UdonSharpBehaviour.UnityEngine.ISerializationCallbackReceiver.OnAfterDeserialize() Trigger: Open a prefab containing UdonSharpBehaviour in Prefab Mode Move a child object or let PrefabStage autosave run Errors repeat, sometimes dozens/hundreds per save Expected: PrefabStage autosave should not throw if a Unity pseudo-null UdonSharpBehaviour or serialized target is encountered. It should skip invalid objects or handle UnityEngine.Object pseudo-null safely. Additional finding: For diagnosis only, I temporarily tested a local guard around the SDK serialization path. The test indicated that the affected object was not a normal C# null reference, but behaved as null through Unity's overloaded UnityEngine.Object null comparison. With that guard in place, the exception stopped. I am not using this as a permanent workaround and do not intend to publish content with a modified SDK. This observation is included only to help identify the likely failure path. Additional observation: I have encountered this issue twice. In both cases, once the issue started occurring in the project, checking out older repository commits did not reliably make the issue disappear. This suggests that the trigger may involve Unity Library/cache/generated SDK state or some project-local serialized state, not only the currently checked out asset files.

Calling GetComponent on a GameObject that has a child with a VRCStation component attached throws the following error: [UdonSharp] Packages/com.vrchat.worlds/Integrations/UdonSharp/Runtime/Libraries/CompilerInternal/GetComponentShim.cs(25,30): Udon runtime exception detected! An exception occurred during EXTERN to 'VRCUdonCommonInterfacesIUdonEventReceiver.__GetProgramVariableType__SystemString__SystemType'. Object reference not set to an instance of an object

The Scale method on Vector classes is intended to scale each component of a vector by the respective component of another vector, and apply the result to the vector whose method was called. This method does not seem to be functioning in Udon. This issue affects all Vector types. Below is a code snippet demonstrating the issue, along with the expected and actual log outputs. Version info: Unity 2022.3.22f1 VRChat SDK - Base 3.10.3 VRChat SDK - Worlds 3.10.3 Vector3Scale.cs: void Start() { var v2ScaleTest = new Vector2(1, 2); v2ScaleTest.Scale(new Vector2(10, 20)); Debug.Log($"Vector2(1, 2, 3).Scale(10, 20, 30) = {v2ScaleTest}"); var v2IntScaleTest = new Vector2Int(1, 2); v2IntScaleTest.Scale(new Vector2Int(10, 20)); Debug.Log($"Vector2Int(1, 2, 3).Scale(10, 20, 30) = {v2IntScaleTest}"); var v3ScaleTest = new Vector3(1, 2, 3); v3ScaleTest.Scale(new Vector3(10, 20, 30)); Debug.Log($"Vector3(1, 2, 3).Scale(10, 20, 30) = {v3ScaleTest}"); var v3IntScaleTest = new Vector3Int(1, 2, 3); v3IntScaleTest.Scale(new Vector3Int(10, 20, 30)); Debug.Log($"Vector3Int(1, 2, 3).Scale(10, 20, 30) = {v3IntScaleTest}"); var v4ScaleTest = new Vector4(1, 2, 3, 4); v4ScaleTest.Scale(new Vector4(10, 20, 30, 40)); Debug.Log($"Vector4(1, 2, 3, 4).Scale(10, 20, 30, 40) = {v4ScaleTest}"); } Output when executed as C#: Vector2(1, 2, 3).Scale(10, 20, 30) = (10.00, 40.00) Vector2Int(1, 2, 3).Scale(10, 20, 30) = (10, 40) Vector3(1, 2, 3).Scale(10, 20, 30) = (10.00, 40.00, 90.00) Vector3Int(1, 2, 3).Scale(10, 20, 30) = (10, 40, 90) Vector4(1, 2, 3, 4).Scale(10, 20, 30, 40) = (10.00, 40.00, 90.00, 160.00) Output when executed as U#: Vector2(1, 2, 3).Scale(10, 20, 30) = (1.00, 2.00) Vector2Int(1, 2, 3).Scale(10, 20, 30) = (1, 2) Vector3(1, 2, 3).Scale(10, 20, 30) = (1.00, 2.00, 3.00) Vector3Int(1, 2, 3).Scale(10, 20, 30) = (1, 2, 3) Vector3Int(1, 2, 3).Scale(10, 20, 30) = (1, 2, 3) Vector4(1, 2, 3, 4).Scale(10, 20, 30, 40) = (1.00, 2.00, 3.00, 4.00)

I was attempting to make what should have been a simple system, ignore data being loaded when it's from the player being restored, but not ignore it when it's the first time you create it. I used the OnPlayerDataUpdated's Info[] output, and found that the item for "Added" would always be called on world load. Similarly, the item for "Restored" was being present even when it's the first time you are in the world. I ended up making a workaround to solve my case, but I'm fairly certain this behavior in the first place is a bug or an oversight due to how rare data needs to be "added" over "restored".

I've found an issue with the Bounds.SetMinMax method in Udon. When using this method, it's expected that the Bounds object it's called on sets its min and max bounds to the supplied Vector3 values respectively. In testing, its values instead seem to stay completely unchanged. This issue does not appear when using the Bounds.min and Bounds.max setters directly. Below is a code snippet demonstrating the issue, along with the expected and actual log outputs. An UdonGraph screenshot is also included for completeness. Version info: Unity 2022.3.22f1 VRChat SDK - Base 3.10.3 VRChat SDK - Worlds 3.10.3 BoundsSetMinMax.cs: void Start() { var boundsTest = new Bounds(new Vector3(1, 2, 3), new Vector3(4, 5, 6)); Debug.Log($"New - {boundsTest}"); boundsTest.SetMinMax(new Vector3(1, 2, 3), new Vector3(4, 5, 6)); Debug.Log($"SetMinMax - {boundsTest}"); boundsTest.min = new Vector3(1, 2, 3); boundsTest.max = new Vector3(4, 5, 6); Debug.Log($"min, max - {boundsTest}"); } Output when executed as C#: New - Center: (1.00, 2.00, 3.00), Extents: (2.00, 2.50, 3.00) SetMinMax - Center: (2.50, 3.50, 4.50), Extents: (1.50, 1.50, 1.50) min, max - Center: (2.50, 3.50, 4.50), Extents: (1.50, 1.50, 1.50) Output when executed as U#: New - Center: (1.00, 2.00, 3.00), Extents: (2.00, 2.50, 3.00) SetMinMax - Center: (1.00, 2.00, 3.00), Extents: (2.00, 2.50, 3.00) min, max - Center: (2.50, 3.50, 4.50), Extents: (1.50, 1.50, 1.50) UdonGraph example:

When performing a System.Object.equals() comparison on TokenType values (as might happen if you do if (token.Type == TokenType.Error) ), two GC allocations seem to occur (in world SDK 3.10.3 - I can't confirm if this happens in-client, but if there's a difference here it makes it effectively impossible to optimize Udon scripts to reduce GC hitching). See attached screenshot - I have some harmony hooks in to apply profiler markers around extern calls. If you need the harmony hooks for comparison, here they are: https://gist.github.com/bdunderscore/c325c6e1fc8d29a6c501c6eda09ca0fc

As an example, if player A blocked player B, and player B enters a station, the OnStationEntered event is not triggered on player's A side. This can break some prefabs or worlds that rely on those events. There may be other events where it could cause some issues, but that's the one event I noted, I didn't tested other events like OnPlayerTriggerEnter.

When a player is on a station, being moved outside the collision of a component with udon and the OnPlayerTriggerExit event, does not actually activate OnPlayerTriggerExit The same goes for OnPlayerTriggerEnter. It's possibly one of the most egregious udon bugs in VRChat, and it's been untouched for years.