World/Udon Bugs & Feature Requests

Checking the equality/inequality of a system-defined enum with equality/inequality operators ( == / != ) will fail. As a result, this example codes in the document don't work as expected: https://creators.vrchat.com/platforms/android/android-best-practices/#2-detect-mobile-players-in-your-world-automatically public override void OnInputMethodChanged(VRCInputMethod inputMethod) { if (inputMethod == VRCInputMethod.Touch) { // Run code for touch input } else { // Run code for non-touch input } } (The UdonGraph version (attached image) also has an identical issue.) Workaround Cast to underlying values and compare them. if ((int)inputMethod == (int)VRCInputMethod.Touch) Analysis UdonSharp compiles the expression inputMethod == VRCInputMethod.Touch into EXTERN, "SystemObject.__Equals__SystemObject__SystemBoolean" Although Object.Equals(Object) is overridden by Enum.Equals(Object) , which the inputMethod may have, with comparing underlying value, this EXTERN seems to call the Object.Equals directly (maybe via reflection API), and it returns the unexpected result (by only comparing the referencing instances). The EXTERN, "SystemObject.__Equals__ comes from here https://github.com/vrchat-community/UdonSharp/blob/22307065bd408dfd163fe46b0b8b701a4efcbc00/Packages/com.vrchat.UdonSharp/Editor/Compiler/Binder/BoundNodes/BoundInvocationExpression.cs#L420 And replacing the System_Object of this line with System_Enum doesn't work because the Enum.Equals is not exposed. Suggestions Temporary, rewrite the example codes using cast operator Expose System.Enum.Equals And replace the EXTERN with System.Enum.Equals

Gravity and Kinematic flags on VRCObjectSync components don't sync correctly right now and also cannot be set correctly while holding the pickup. To set gravity or kinematic flags, VRChat added two new methods for us: https://udonsharp.docs.vrchat.com/vrchat-api/#vrcobjectsync (they are supposed to behave like a synced variable) There are two bugs related to this: ~ Bug 1: ~ All you need is to create a pickup that has no gravity and then toggle the gravity flag on the VRCObjectSync component with an external button after claiming ownership. Then you let different people in the world pick up the pickup and drop it (to show their own local state). In my tests, this resulted in a pickup where the gravity flag is wildly different on each client and only syncs occasionally or not at all. They would see the pickup drop on my end, but when they pick it up it has no gravity for them. ~ Bug 2: ~ All you need is to create a pickup that has no gravity and then toggle the gravity flag on the VRCObjectSync component in OnPickupUseDown() . In my tests, this resulted in a pickup where the gravity stays enabled after the first OnPickupUseDown() and I am unable to turn gravity off again. To check gravity, the pickup is dropped. You can also just test it out here: Right setup: Bug 1 / Left setup: Bug 2 https://vrchat.com/home/world/wrld_9cefd5ec-4492-43c5-8cd3-05036c494556 Additional note: Since we only got a setter and not a getter method, we are left in the dark here when it comes to analyzing the problem. Reading out the local rigidbody state doesn't give us access to the real synced state. A getter method should be added.

"Op Division" of int node crashes VRChat.exe when the divisor is zero. However, when running in Unity editor it only stops the UdonBehaviour with appropriate error message. --- The head of crash report error.log (local testing and published world case) VRChat by VRChat [version: Unity 2018.4.20f1_008688490035] GameAssembly.dll caused an Integer Divide by Zero (0xc0000094) in module GameAssembly.dll at 0033:2102cb7d. -- The message appears in Unity editor console (running in Unity editor case) [UdonBehaviour] An exception occurred during Udon execution, this UdonBehaviour will be halted. VRC.Udon.VM.UdonVMException: The VM encountered an error! Exception Message: An exception occurred during EXTERN to 'SystemInt32.__op_Division__SystemInt32_SystemInt32__SystemInt32'. Parameter Addresses: 0x00000001, 0x00000002, 0x00000000 Attempted to divide by zero.

When adding [UdonBehaviourSyncMode(BehaviourSyncMode.NoVariableSync)] to an udon# class, It will just continue using the last setting. For example if you add [UdonBehaviourSyncMode(BehaviourSyncMode.Continuous)] and then compile, then change it to [UdonBehaviourSyncMode(BehaviourSyncMode.NoVariableSync)] and compile again, you get the expected behavior, and calling SendCustomNetworkEvent() works. If you then change it to [UdonBehaviourSyncMode(BehaviourSyncMode.None)] and compile, then change it to [UdonBehaviourSyncMode(BehaviourSyncMode.NoVariableSync)] and compile again It will continue to behave exactly as if it's still set to None. SendCustomNetworkEvent() does not work. This is on an object that doesn't have any other scripts on it. I haven't tested the case with other scripts. You can look at the debug inspector to confirm that this is what is happening. From the documentation: "NoVariableSync: Enforces that there are no synced variables on the behaviour, hides the sync mode selection dropdown, and allows you to use the behaviours on GameObjects that use either Manual or Continuous sync." It seems like the case where a script using NoVariableSync being used on an object that doesn't have another script on it may have been overlooked. Since I'm updating a script in a prefab I'm releasing from None to NoVariableSync because I want to use network events now, it's not going to work for anyone updating to the new version. I am forced to set it to Continuous. Does anyone know if it makes any difference to bandwidth usage?

This was reported as fixed in 2024.4.1p3 but it looks like the problem crept back in and exists in SDK 3.8.2 / 2025.3.1 (haven't tested any other versions). Since the previous canny was closed out as complete, thought I'd open a new one. Prior bug report on this issue: https://feedback.vrchat.com/udon/p/braces-inside-strings-in-vrcjson-can-fail-to-deserialize // This works if(VRCJson.TryDeserializeFromJson("\"{\"data\":\"test\"}", out DataToken token2)) Debug.LogError("Failed to deserialize JSON"); else Debug.Log("Successfully deserialized JSON"); // This fails. Only difference is the braces after the word test in the JSON string. Number of braces or their configuration doesn't seem to make a difference. if(VRCJson.TryDeserializeFromJson("{\"data\":\"test{}\"}", out DataToken token1)) Debug.LogError("Failed to deserialize JSON"); else Debug.Log("Successfully deserialized JSON"); Thanks! -Tea

On the documentation page for Input Events ( https://creators.vrchat.com/worlds/udon/input-events/ ) "InputDrop" is said to be true for releasing the grip buttons on controllers other than vive wands or some WMR controllers. I've been doing a few tests with the input mappings to see how they behave between players using Vive wands and other controller types. So far, I've found that the "release grip" condition for InputDrop becoming true is only the case (for a single frame, which is good) when using Hand Tracking on Quest standalone, but I was unable to trigger it from releasing grip any other way. Oculus controllers - both from PCVR through SteamVR via Virtual Desktop, and on the standalone version - from my testing cannot fire InputDrop at all. Index controllers also can't fire it all either. I feel as though either this needs to be changed in the client or the documentation needs to be updated... With this in mind though, currently a usable workaround is to just do the "release grip" check on our own via Udon, using the InputGrab event and checking for False. P.S: I also found that the OnInputMethodChanged event always says SteamVR2 when playing from PCVR, regardless of the actual input type, but this was already reported in another post. Also, The input method for Hand Tracking on Android returns a value of 19, which is not documented as the highest value shown on the website is 18. My IDE says that it does exist however with an enum called "VRCInputMethod.Count" instead of using "VRCInputMethod.QuestHands"? Still strange.

Repro: var bounds = new Bounds( Vector3.zero , Vector3.one ); Debug.Log("Bounds: " + bounds.size); bounds.Expand(100f); Debug.Log("Bounds: " + bounds.size);

Ownership can permanently desync between clients in an unexpected way The included script can generate such a desync, please assign a TMP text field to view it, then join with 2 clients --- Of note for anyone experiencing this, I've had some success mitigating it by overriding OnOwnershipRequest and returning true public override bool OnOwnershipRequest(VRCPlayerApi requestingPlayer, VRCPlayerApi requestedOwner) { return true; }

Sometimes, upon joining a world, OnPlayerDataUpdated() fires with infos containing all of the existing keys, but the State on each PlayerData.Info is set to Added instead of Restored. I have not found any rhyme or reason to why this happens, but it seems to be happening more frequently lately. This is happening on whatever client version was recent as of 2025/09/09.

There is an undocumented limit on Network IDs. If you assign a Network ID beyond 10 000 to a PlayerObject its persistence features will break while the UdonBehaviour itself still functions and syncs. ClientSim throws the following error: ran out of player persistence view ids In-game testing results in Removed some Player Persistence metadata that had invalid IDs. errors. Apparently there is a limit of 100 000 for Network IDs in general, its way less likely to hit this, but this also seems undocumented. The difference in limit for PlayerObjects and standard UdonBehaviour objects is confusing and the provided errors don't accurately explain how to solve this issue. The Network ID Utility also does not seem to take this limit for Player Objects into account and does not warn or ensure a lower ID is assigned to the persistent objects. Furthermore, the Network ID Utility crashes on projects with this many Network IDs, but this was already documented here: https://feedback.vrchat.com/sdk-bug-reports/p/network-id-utility-has-massive-performance-issues