Lethe Launcher

A custom launcher for Limbus Company that provides intelligent file management, Steam integration, and modding support via BepInEx.

Features

🚀 Smart File Management

• Manifest-based updates: Downloads only changed or missing files
• XXHash verification: Ensures file integrity with fast checksum validation
• Local copy optimization: Automatically copies files from existing Steam installation to avoid re-downloading
• Steam path detection: Uses Windows registry to automatically locate Steam installation
• Progress tracking: Real-time download progress with file count and byte progress

🎮 Game Integration

• Direct game launch: Calls UnityMain from UnityPlayer.dll for seamless startup
• BepInEx support: Loads doorstop.dll to enable mod framework integration
• Steam compatibility: Works with existing Steam installations of Limbus Company

📊 Logging & Diagnostics

• Dual logging: Outputs to both console and lethe-launcher.log file
• Detailed diagnostics: Comprehensive error reporting with file paths and Windows error codes
• Session tracking: Timestamped logs with clear session boundaries
• Configuration logging: Tracks all configuration changes and settings

⚙️ Configuration

• Configuration file: lethe-launcher.ini for customizable behavior
• Silent mode: DisableAutoUpdate=true hides UI and launches game directly
• Flexible deployment: Single executable with minimal dependencies

Building

Prerequisites

• .NET 8.0 SDK
• Windows (for final deployment)

Build Command

dotnet publish --configuration Release

Output

The build creates a distribution-ready package at:

bin/Release/net8.0/win-x64/distribution/
├── LimbusCompany.exe          (74MB - Main launcher)
├── av_libglesv2.dll          (4.2MB - OpenGL graphics)
├── libHarfBuzzSharp.dll      (1.5MB - Text rendering)
└── libSkiaSharp.dll          (9.0MB - Skia graphics)

Total package size: ~89MB

Deployment

Required Files Structure

Place the launcher in the game directory with this structure:

GameDirectory/
├── LimbusCompany.exe          (Launcher - renamed for stealth)
├── UnityPlayer.dll            (Unity engine)
├── UnityMain.dll              (Unity entry point)
├── BepInEx/
│   └── doorstop/
│       └── doorstop.dll       (BepInEx loader)
├── av_libglesv2.dll          (OpenGL support)
├── libHarfBuzzSharp.dll      (Text rendering)
└── libSkiaSharp.dll          (Graphics library)

Configuration File

Create lethe-launcher.ini in the same directory:

DisableAutoUpdate=false

Options:

• DisableAutoUpdate=false - Show UI and perform file synchronization
• DisableAutoUpdate=true - Silent mode, skip UI, launch game directly

How It Works

Startup Sequence

1. Configuration Loading: Reads lethe-launcher.ini settings
2. Mode Detection: Checks if auto-update is disabled
3. File Synchronization (if enabled):
   • Downloads manifest from remote server
   • Checks local files against manifest (size + XXHash)
   • Attempts to copy missing files from Steam installation
   • Downloads remaining files from remote server
4. Game Launch:
   • Loads UnityPlayer.dll (required by doorstop)
   • Loads BepInEx/doorstop/doorstop.dll (enables mods)
   • Calls UnityMain(0, 0, "", 0x1) to start game

File Verification Process

1. Size Check: Quick file size comparison
2. Hash Verification: XXHash checksum validation for integrity
3. Local Copy Attempt: Check Steam installation for existing files
4. Remote Download: Download only if local copy unavailable or invalid

Steam Integration

• Reads Steam installation path from Windows registry: HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Valve\Steam
• Constructs game path: {SteamPath}/steamapps/common/Limbus Company
• Falls back to default path if registry read fails

Technical Details

Dependencies

• Avalonia UI: Cross-platform UI framework
• System.Text.Json: JSON manifest parsing
• System.IO.Hashing: XXHash implementation for file verification
• Microsoft.Win32: Windows registry access for Steam path detection

File Formats

• Manifest: JSON format containing file entries with paths, sizes, and XXHash checksums
• Configuration: INI-style key=value pairs
• Logs: Timestamped plain text with session markers

Error Handling

• Comprehensive error logging with specific error codes
• Graceful fallbacks for registry access failures
• File existence verification before DLL loading
• Detailed path resolution for debugging

Performance Optimizations

• XXHash for fast file verification (faster than MD5/SHA)
• Local file copying to minimize network usage
• Streaming downloads with progress callbacks
• Parallel file existence checks

Logging

All operations are logged to lethe-launcher.log with timestamps:

=== Lethe Launcher Started at 2025-10-26 12:43:48 ===
[12:43:48] Configuration loaded from lethe-launcher.ini:
[12:43:48]   DisableAutoUpdate = false
[12:43:49] Downloaded manifest: 150 files, 2048576 bytes
[12:43:49] Starting file synchronization...
[12:43:50] Copied from local: Data/file.dat (1.2 MB)
[12:43:51] Downloaded: Assets/texture.png (512 KB)
[12:43:52] Update complete. Starting game...
[12:43:52] ✓ Found UnityPlayer.dll at: C:\Game\UnityPlayer.dll
[12:43:52] ✓ UnityPlayer.dll loaded successfully
[12:43:52] ✓ doorstop.dll loaded successfully
[12:43:52] UnityMain returned: 0