Archipelago/docs/sphinx/AddingGames.md

Adding Games to Archipelago

This guide is going to try and be a broad summary of what is required to add a game integration to Archipelago.

This guide is not an in-depth tutorial on video game modification nor is it a getting started guide to software or video game development. The intent is to provide information, tips, and tools, to assist a would-be modder in adding a game integration to Archipelago.

There are two key steps to incorporating a game into Archipelago:

• Game Modification
• Archipelago Server Integration

This document covers game modification. Information on creating the Archipelago server integration may be found in the Adding Archipelago Integration.

Game Modification

One half of the work required to integrate a game into Archipelago is the development of the game client. This is typically done through a modding API or other modification process, this is described further down.

As an example, modifications to a game typically include:

• Hooking into when a "location check" is completed.
• Networking with the Archipelago server.
• Optionally, UI or HUD updates to show status of the multiworld session or Archipelago server connection.

Engine Identification

This is a good way to make the modding process much easier. Being able to identify what engine a game was made in is critical. The first step is to look at a game's files. Let's go over what some game files might look like. It’s important that you be able to see file extensions, so be sure to enable that feature in your file viewer of choice.

Examples

Proprietary Game Engine

This is the game Creepy Castle. It’s your worst-case scenario as a modder. All that’s present here is an executable file and some meta-information that Steam uses. You have basically nothing here to work with. If you want to change this game, the only option you have is to do some pretty nasty disassembly and reverse engineering work, which is outside the scope of this tutorial.

Unity Game Engine

Here’s the release files for another game, Heavy Bullets. We see a .exe file, like expected, and a few more files. hello.txt is a text file, which we can quickly skim in any text editor. Many games have text files in their directories in some form, usually with a name like README.txt. They may contain information about a game, such as a EULA, terms of service, licensing information, credits, or other general info about the game. You typically won’t find anything too helpful here, but it never hurts to check.

In this case, it contains some credits and a changelog for the game, so nothing too important. steam_api.dll is a file you can safely ignore, it’s just some code used to interface with Steam. The directory HEAVY_BULLETS_Data, however, has some good news.

The contents of the HEAVY_BULLETS_Data directory follow the pattern typically used by the Unity game engine. If you look in the sub-folders, you’ll seem some .dll files which affirm our suspicions. Telltale signs for this are directories titled Managed and Mono, as well as the numbered, extension-less level files and the sharedassets files. Also keep your eyes out for an executable with a name like UnityCrashHandler, that’s another dead giveaway.

XNA/FNA

This is the game contents of Stardew Valley. A lot more to look at here, but there are some key takeaways. Notice the .dll files which include “CSharp” in their name. Also notice the Content. These signs point to a game based on the .NET framework and many games following this style will use the XNA game framework as the base to build their game from.

Gato Roboto

Our last example is the game Gato Roboto. Notice the file titled data.win. This immediately tips us off that this game was made in GameMaker.

Open or Leaked Source Games

As a side note, many games have either been made open source, or have had source files leaked at some point. This can be a boon to any would-be modder, for obvious reasons. Always be sure to check - a quick internet search for "(Game) Source Code" might not give results often, but when it does you're going to have a much better time.

Be sure never to distribute source code for games that you decompile or find if you do not have express permission from the author to do so, nor to redistribute any materials obtained through similar methods, as this is illegal and unethical.

Modifying Release Versions of Games

Some developers are kind enough to deliberately leave you ways to alter their games, like modding tools, but these are often not geared to the kind of work you'll be doing and may not help much. This is usually assessed on a case-by-case basis. Games with large modding communities typically grow around the tooling a developer provides or they grow around the fact that the game is easy to modify in the first place.

As a general rule, any modding tool that lets you write actual code is something worth using.

Creating the Mod

Research

The first step is to research your game. Even if you've been dealt the worst hand in terms of engine modification, it's possible other motivated parties have concocted useful tools for your game already. Always be sure to search the Internet for the efforts of other modders.

Analysis Tools

Depending on the game’s underlying engine, there may be some tools you can use either in lieu of or in addition to existing game tools.

ILSpy

You can download ILSpy and see more info about it on the ILSpy GitHub repository homepage.

The first tool in your toolbox is ILSpy. ILSpy is a .NET decompiler. The purpose of this program is to take a compiled .NET assembly (.DLL or .EXE file) and turn it back into human-readable source code. A file is a .NET assembly when it was created through the compilation of any programming language targeting the .NET runtime. Usually, the programming language in question is C# (C Sharp).

Unity games are a combination of native code (compiled in a "native language" such as C++) and .NET code. Most game developers will write the bulk of their code as C# and this will be compiled by Unity into .NET assemblies. Those files may then be decompiled with ILSpy to allow you to see the original source code of the game.

For Unity games, the file you’ll typically want to open will be the file (Data Folder)/Managed/Assembly-CSharp.dll, as pictured below:

For other .NET based games, which are not made in Unity, the file you want is usually just the executable itself.

Although the names of classes, methods, variables, and more will be preserved, code structures may not remain entirely intact. This is because compilers will often subtly rewrite code to be more optimal, so that it works the same as the original code but uses fewer resources. Compiled C# files also lose comments and other documentation.

UndertaleModTool

You can download and find more info on UndertaleModTool on the UndertaleModTool GitHub repository homepage. This is currently the best tool for modifying games made in GameMaker, and supports games made in both GameMaker Studio 1 and 2. It allows you to modify code in GameMaker Language (GML).

Use the tool to open the data.win file to see game data and code. Like ILSpy, you won’t be able to see comments. In addition, you will be able to see and modify many hidden fields on items that GameMaker itself will often hide from creators.

Fonts in particular are notoriously complex, and to add new sprites you may need to modify existing sprite sheets.

What Modifications You Should Make to the Game

We talked about this briefly in Game Modification section. The next step is to know what you need to make the game do now that you can modify it. Here are your key goals:

• Modify the game so that checks are shuffled
• Know when the player has completed a check, and react accordingly
• Listen for messages from the Archipelago server
• Modify the game to display messages from the Archipelago server
• Add interface for connecting to the Archipelago server with passwords and sessions
• Add commands for manually rewarding, re-syncing, forfeiting, and other actions

To elaborate, you need to be able to inform the server whenever you check locations, print out messages that you receive from the server in-game so players can read them, award items when the server tells you to, sync and re-sync when necessary, avoid double-awarding items while still maintaining game file integrity, and allow players to manually enter commands in case the client or server make mistakes.

Refer to the Network Protocol documentation for how to communicate with Archipelago's servers.

Modifying Console Games

My Game is a recent game for the PS4/Xbox-One/Nintendo Switch/etc

Most games for recent generations of console platforms are inaccessible to the typical modder. It is generally advised that you do not attempt to work with these games as they are difficult to modify and are protected by their copyright holders. Most modern AAA game studios will provide a modding interface or otherwise deny modifications for their console games.

There is some traction on this changing as studios are finding ways to include game modifications in console games.

My Game isn’t that old, it’s for the Wii/PS2/360/etc

This is very complex, but doable. It is typically necessary to use Assembly (ASM) to modify these games. If you don't have good knowledge of stuff like Assembly programming, this is not where you want to learn it. There exist many disassembly and debugging tools, but more recent content may have lackluster support.

My Game is a classic for the SNES/Sega Genesis/etc

That’s a lot more feasible. There are many good tools available for understanding and modifying games on these older consoles, and the emulation community will have figured out the bulk of the console’s secrets. Look for debugging tools, but be ready to learn assembly. Old consoles usually have their own unique dialects of ASM you’ll need to get used to.

Also make sure there’s a good way to interface with a running emulator, since that’s the only way you can connect these older consoles to the internet. There are also hardware mods and flash carts, which can do the same things an emulator would when connected to a computer. These will require the same sort of interface software to be written in order to work properly--from your perspective the two won't really look any different.

My Game is an exclusive for the Super Baby Magic Dream Boy. It’s this console from the Soviet Union that-

Unless you have a circuit schematic for the Super Baby Magic Dream Boy sitting on your desk, no. Obscurity is your enemy – there will likely be little to no emulator or modding information, and you’d essentially be working from scratch. You're welcome to try and break ground on something like this, but understand that community support will range from "extremely limited" to "nonexistent".

How to Distribute Game Modifications

NEVER EVER distribute anyone else's copyrighted work UNLESS THEY EXPLICITLY GIVE YOU PERMISSION TO DO SO!!!

The right way to distribute modified versions of a game's binaries is to distribute binary patches.

The common theme is that you can’t distribute anything that wasn't made by you. Patches are files that describe how your modified file differs from the original one without including the original file's content, thus avoiding the issue of distributing someone else’s original work.

Users who have a copy of the game just need to apply the patch, and those who don’t are unable to play.

Patches

The following patch formats are commonly seen in the game modding scene.

IPS

IPS patches are a simple list of chunks to replace in the original to generate the output. It is not possible to encode moving of a chunk, so they may inadvertently contain copyrighted material and should be avoided unless you know it's fine.

UPS, BPS, VCDIFF (xdelta), bsdiff

Other patch formats generate the difference between two streams (delta patches) with varying complexity. This way it is possible to insert bytes or move chunks without including any original data. Bsdiff is highly optimized and includes compression, so this format is used by APBP.

Only a bsdiff module is integrated into AP. If the final patch requires or is based on any other patch, convert them to bsdiff or APBP before adding it to the AP source code as "basepatch.bsdiff4" or "basepatch.apbp".

APBP Archipelago Binary Patch

Starting with version 4 of the APBP format, this is a ZIP file containing metadata in archipelago.json and additional files required by the game / patching process. For ROM-based games the ZIP will include a delta.bsdiff4 which is the bsdiff between the original and the randomized ROM.

To make using APBP easy, they can be generated by inheriting from Patch.APDeltaPatch.

Mod files

Games which support modding will usually just let you drag and drop the mod’s files into a folder somewhere. Mod files come in many forms, but the rules about not distributing other people's content remain the same. They can either be generic and modify the game using a seed or slot_data from the AP websocket, or they can be generated per seed.

If the mod is generated by AP and is installed from a ZIP file, it may be possible to include APBP metadata for easy integration into the Webhost by inheriting from Patch.APContainer.