Unity with MoonSharp: A Lua Scripting Example

This example demonstrates how to integrate Lua scripting into a Unity project using the MoonSharp interpreter. The provided LuaTest.cs MonoBehaviour showcases the basics of how to call Lua functions from C#, expose C# methods to Lua, and access Lua variables from C#.

Prerequisites

• Tested with Unity 2022.3. Should work with Unity 2018 and above.
• MoonSharp library (which serves as the Lua script engine)

Overview

Calling Lua Functions from C#

The example contains an update function written in Lua, which is called during Unity's Update method:

function update()
    local currentTime = time()  -- Get time from C# script
    print('Time since startup: ' .. currentTime)
end

In C#, the Lua update function is fetched as a DynValue and then invoked during Unity's Update:

luaUpdateFunction = luaScript.Globals.Get("update");
...
if (luaUpdateFunction.Type == DataType.Function)
{
    luaScript.Call(luaUpdateFunction);
}

Exposing C# Functions to Lua

C# functions can be registered with the Lua environment to make them callable from Lua scripts. In the provided example:

LuaPrint allows Lua to log messages to the Unity console. CalculateMagnitude computes the magnitude given two float arguments. GetTime fetches the time since the application started.

luaScript.Globals["print"] = (Action<string>)LuaPrint;
luaScript.Globals["magnitude"] = (Func<float, float, float>)CalculateMagnitude;
luaScript.Globals["time"] = (Func<float>)GetTime;

Accessing Lua Variables from C# Lua variables can be accessed from C# after they've been defined in the Lua environment. For instance, after defining x in Lua, it's fetched in C# as follows:

DynValue xValue = luaScript.Globals.Get("x");
Debug.Log("Getting variable x from state: " + xValue.Number);

How to Run the Example

• Ensure you have Unity 2022.3 installed.
• Import the MoonSharp library into your Unity project.
• The LuaTest monobehaviour is attached to the camera in the example code. Attach it to any game object.
• Run the scene. Observe the Unity console for messages logged from both C# and Lua.
• Important Notes
• Always wrap your DoString calls with a try-catch to handle any Lua runtime errors gracefully.
• Ensure that the C# methods you expose to Lua have the correct signature to match the expected Lua function calls.