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Outer Wilds Mod Loader

Prepatchers

In certain contexts you may need to edit game files before start. This is where prepatchers come in. Prepatchers are run by OWML directly before the game starts, allowing you to modify game files you would otherwise not be able to.

To create a prepatcher you’ll need a separate project from your mod. This can be done by creating a new project in your solution with the executable type, it should automatically build to your mod folder.

  • DirectoryMyMod/
    • DirectoryMyPrepatcher/
      • MyPrepatcher.csproj
      • MyPrepatcher.cs
    • manifest.json

Now in your mod manifest you need to set the patcher field to the path of the executable relative to the root of the mod folder.

{
  "filename": "MyPrepatcher.dll",
  "author": "Me",
  "name": "My cool mod",
  "uniqueName": "Bwc9876.MyMod",
  "version": "0.0.1",
  "owmlVersion": "2.9.0",
  "prepatcher": "MyPrepatcher.exe"
}

Creating A Prepatcher

Section titled “Creating A Prepatcher”

A prepatcher is a simple console app that OWML executes, it’s only passed the location of your mod folder. However, it is possible to get the game’s location by doing AppDomain.CurrentDomain.BaseDirectory:

public static void Main(string[] args)
{
    var modPath = args.Length > 0 ? args[0] : ".";
    var gamePath = AppDomain.CurrentDomain.BaseDirectory;

    Console.WriteLine($"Mod Path: {modPath}");
    Console.WriteLine($"Game Path: {gamePath}");

    // DoStuff(modPath, gamePath);
}

Keep in mind the ModHelper is not available in a prepatcher. You’ll need to have the prepatcher include libraries like Newtonsoft.Json to read and write JSON files.

As an example, Quantum Space Buddies utilizes a pre-patcher. You can use this as an example. Notice how it also needs to set this as patcher in its manifest in order for OWML to know to run it.

Logging

Section titled “Logging”

Due to a lack of ModHelper, you’ll need to use Console.WriteLine to log information. This will not output to the manager window. To test prepatchers, we recommend you launch OWML.Launcher.exe in a terminal directly to properly see stdout.

If a prepatcher errors it should usually be outputted to the manager window as OWML is setup to catch and log any exceptions thrown by the prepatcher.