Udon Lua

Lua interpreter in VRChat. This interpreter uses the original Lua 5.4.6 implemented in C converted with wasm2usharp.

The world is available on VRChat.

How to build Lua to UdonSharp

Tested environment

• Ubuntu 22.04 (on WSL 2)
• CMake 3.25.1
• WASI SDK 22.0
• Binaryen 117
• wasm2usharp 0.1.0

Install dependencies

# Install CMake
sudo apt update && sudo apt upgrade
sudo apt install cmake

# Get WASI SDK
wget https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-22/wasi-sdk-22.0-linux.tar.gz
tar xf wasi-sdk-22.0-linux.tar.gz

# Get Binaryen
wget https://github.com/WebAssembly/binaryen/releases/download/version_117/binaryen-version_117-x86_64-linux.tar.gz
tar xf binaryen-version_117-x86_64-linux.tar.gz

# Get wasm2usharp
wget https://github.com/raii-x/wasm2usharp/releases/download/v0.1.0/wasm2usharp-x86_64-unknown-linux-gnu.tar.gz
mkdir wasm2usharp
tar xf wasm2usharp-x86_64-unknown-linux-gnu.tar.gz -C wasm2usharp

# Set environment variables
export WASI_SDK_PATH=`pwd`/wasi-sdk-22.0
export PATH=`pwd`/binaryen-version_117/bin:$PATH
export PATH=`pwd`/wasm2usharp:$PATH

Build Lua

# Current directory is the root of this repository
cmake -S lua -B lua/build
cmake --build lua/build
wasm2usharp lua/build/lua.wasm -o Assets/Scripts/Lua.cs

Changes from original Lua

• Some functions in Lua standard libraries that are not supported in WASI are disabled.
• Ruby's implementation for Asyncify (lua/rb_wasm) is used to use setjmp/longjmp and split long processing to multiple frames (in lvm.c).
• Functions for Udon are implemented in runtime.c.

License

The source code for Lua (MIT) and Ruby (2-clause BSD) and the UdonSharp code compiled from them are under the original licenses. The other source code I have created is under CC0.