LegacyForge

An SKSE-style mod loader for Minecraft Legacy Edition. LegacyForge injects into the game process at runtime, hooks key engine functions, and hosts the .NET runtime to load C# mods. Zero game source modifications required.

How It Works

1. LegacyForge.exe launches the game in a suspended state and injects LegacyForgeRuntime.dll
2. The runtime DLL uses PDB debug symbols to locate game functions (MinecraftWorld_RunStaticCtors, Minecraft::tick, etc.)
3. MinHook detours those functions to insert mod lifecycle callbacks
4. The .NET CoreCLR runtime is hosted inside the game process via hostfxr
5. LegacyForge.Core discovers and loads C# mod assemblies from the mods/ folder
6. Mods use the LegacyForge.API to register blocks, items, entities, and subscribe to game events using Fabric-style namespaced string IDs

Project Structure

ModLoader/
├── LegacyForge.Launcher/       C# launcher (the exe users run)
├── LegacyForgeRuntime/          C++ DLL (injected into game process)
├── LegacyForge.Core/            C# mod management (loaded inside game)
├── LegacyForge.API/             C# mod API (what mod authors reference)
└── ExampleMod/                  Sample mod for reference

Building

Prerequisites

• Visual Studio 2022 or later (with C++ and .NET workloads)
• .NET 8.0 SDK or later
• CMake 3.24 or later
• The game must be compiled with PDB generation

Build Steps

C++ Runtime DLL:

cd LegacyForgeRuntime
cmake -B build -A x64
cmake --build build --config Release

C# Projects:

dotnet build LegacyForge.sln

Usage

1. Build LegacyForge (see above)
2. Copy the output files to a folder:
   • LegacyForge.exe
   • LegacyForgeRuntime.dll
   • LegacyForge.Core.dll
   • LegacyForge.API.dll
3. Create a mods/ folder and drop mod DLLs in it
4. Run LegacyForge.exe -- it will ask for the game exe path on first launch
5. The game starts with mods loaded

Writing a Mod

Create a new .NET 8 class library and reference LegacyForge.API:

using LegacyForge.API;

[Mod("mymod", Name = "My Mod", Version = "1.0.0", Author = "You")]
public class MyMod : IMod
{
    public void OnInitialize()
    {
        var myBlock = Registry.Block.Register("mymod:cool_block",
            new BlockProperties()
                .Material(MaterialType.Stone)
                .Hardness(2.0f)
                .Resistance(10f));

        Logger.Info("My Mod loaded!");
    }
}

Build it, copy the DLL to mods/, and launch via LegacyForge.

License

MIT