LCGUdonSharp Overview

Documentation version: 0.3.6 · Release notes

LCGUdonSharp (com.logiccuteguy.lcgudonsharp) is an interface-enabled UdonSharp compiler for VRChat. It extends UdonSharp with C# interfaces, build-time async/await, synchronous try/catch/finally, C# collections and JSON, extended language constructs, and a manual packet networking layer — while keeping every modified source file inside Packages/com.logiccuteguy.lcgudonsharp instead of the VRChat SDK or Assets.

:::info Status Interfaces, synchronous exceptions, async lowering, and extended-language support are ready for world testing. Manual packet networking ([LCGPacket] / LCGNetworkZone) is experimental — its wire protocol may change between versions. :::

What's new in 0.3.6

Object motion now uses a bounded latest-state queue with per-recipient batching, congestion backoff, remote interpolation and bounded prediction.
Zone entry and OnPlayerRestored recover scene-field and object snapshots with bounded retries that stop when the player exits.
Disconnect ownership recovery preserves valid member ownership and repairs reassignment through ownership callbacks; player departure matching prefers identity over reused or invalid IDs.
Packet receivers can recover their binding from serialized compiled programs after a domain reload clears the source-program cache.
New native/LCG lamp, moving-cube and opt-in high-bandwidth examples include wired prefabs and Thai setup guidance.

Recompile all UdonSharp programs and rebuild the world after updating. Older builds cannot decode the 0.3.6 motion batch envelope.

Features

Feature	What you get
C# Interfaces	Source-defined interfaces implemented by `UdonSharpBehaviour` classes — method calls, parameters, return values, properties, multiple implementations, interface arrays.
Async/Await	Build-time lowering for `await Task.Yield()`, `await Task.Delay(int)`, and one VRChat SDK await per behaviour (string/image downloads, video, GPU readback, serialization, Creator Economy).
Synchronous Exceptions	Compiler-managed `try`/`catch`/`finally`, explicit `throw`s, rethrow, and guarded null, index, and integral divide/modulo failures — without relying on unavailable Udon exception opcodes.
Extended Language	`ref`/`out` (including `out var` and recursion), closed generics, interface diamonds, LINQ lambdas with captures, proven `dynamic`, array-backed `Span<T>`.
C# Collections & JSON	Exact `List<T>` and `Dictionary<TKey,TValue>` syntax lowered to `DataList`/`DataDictionary`, plus a VRCJson-backed `System.Text.Json` facade and manual synced-collection payloads.
Manual Packet Networking (experimental)	`[LCGPacket]` fields and methods with versioned frames, authority checks, replay protection, field coalescing, verified-sender callbacks, targeted PlayerObject delivery.
Network Zones	`LCGNetworkZone` scopes packet recipients and ownership to a trigger volume; manual object-sync replaces `VRC_ObjectSync`, Continuous behaviours without synced fields are supported, and native sync passthrough is available as an explicit instance-wide compatibility option.
Clean Installation	Automatic, idempotent setup with backup/restore — no modified files inside `com.vrchat.worlds` or `Assets/`. Installer state lives in `ProjectSettings/LogicCuteGuy.LCGUdonSharp.json`; SDK backups live under `Library/LogicCuteGuy.LCGUdonSharp`.

Key terms

Term	Meaning
Program asset (`UdonSharpProgramAsset`)	The asset paired with one U# script: `MyScript.cs` ↔ `MyScript.asset`, in the same folder with the same basename.
U# assembly definition (`UdonSharpAssemblyDefinition`)	An asset that registers one `.asmdef` for UdonSharp compilation through its `sourceAssembly` field. This is not a compiled program asset.
Assembly scanning	`Assembly-CSharp` is always included. Every other assembly containing U# behaviours needs a U# assembly-definition asset.
Extern	A Unity/SDK method mapped to a built-in Udon node. Faults raised inside an extern cannot be caught by compiler-managed `try`/`catch`.
Packet frame	A versioned serialized message sent by a `[LCGPacket]` field write or packet-method call.

How It Works

1. Automatic installer

After the package is imported, a small bootstrap assembly (Editor/LCGUdonSharpInstaller.cs) runs automatically:

1. Verify VRChat Worlds SDK 3.10.5 is installed
2. Back up SDK-bundled Integrations/UdonSharp
   → Library/LogicCuteGuy.LCGUdonSharp/Backups
3. Install the interface-enabled compiler at
   → Packages/com.logiccuteguy.lcgudonsharp/UdonSharp
4. Remove the SDK-bundled copy so Unity sees
   exactly one set of UdonSharp.* assemblies

Setup is idempotent — if an SDK/package refresh restores the bundled copy, setup runs again. On any SDK version other than 3.10.5, setup stops instead of modifying an untested package.

Everything setup writes outside the package source:

Path	Purpose
`ProjectSettings/LogicCuteGuy.LCGUdonSharp.json`	Installer state, SDK version, and automatic-setup suspension flag.
`Library/LogicCuteGuy.LCGUdonSharp/Backups`	SDK-bundled UdonSharp backups used by repair and restore.
`Library/LogicCuteGuy.LCGUdonSharp`	Installer workspace.

2. Compiler extensions

The compiler keeps the original UdonSharp namespaces and assembly names, then adds lowering passes:

Your C# source
   │
   ├─ interfaces ─────────► program-variable / custom-event ABI calls
   ├─ async/await ────────► frame-pool continuation lowering
   ├─ try/catch/finally ──► hidden payload state + guarded control flow
   ├─ ref/out, closures,
   │  closed generics,
   │  dynamic, Span<T> ───► concrete array/offset/length locals + loops
   ├─ List/Dictionary/JSON ► DataList/DataDictionary + VRCJson helpers
   └─ [LCGPacket] ────────► versioned packet frames + mailbox delivery
   │
   ▼
Udon assembly (runs in VRChat)

3. Manual packet networking

[LCGPacket] does not use native Udon variable sync. Instead:

Assigning a packet field queues a send — repeated assignments in one frame are coalesced to the latest value; unchanged values are skipped; ForceSendPacket(nameof(field)) bypasses suppression.
Packet methods are delivered through a PlayerObject mailbox; SendCustomNetworkEvent(...) is lowered to packet delivery only when the target method has [LCGPacket].
Frames are versioned and validated with authority checks and replay protection.
Owners provide snapshots when players are restored; departing-player state is discarded.

Guides

Acknowledgements

LCGUdonSharp builds on UdonSharp, originally created by Merlin, and on the VRChat Worlds SDK. The compiler retains UdonSharp's original namespaces and assembly names so existing projects continue to work unchanged.

What's new in 0.3.6​

Features​

Key terms​

How It Works​

1. Automatic installer​

2. Compiler extensions​

3. Manual packet networking​

Guides​

Acknowledgements​

License​