The problem
In Total War: WARHAMMER III multiplayer campaigns, each human needs their own faction. That makes teaching a friend awkward, doubles every battle in co-op, and turns a 2v2 into four factions. Players wanted to run one faction together, but the lobby simply refuses two players on the same pick, and nothing in the game's modding tools can change that.
What I built
A mod with two halves. The native half is a C DLL that finds its targets in the running game by byte signature and patches them in memory, never touching the executable on disk. Seven patches let several players pick the same faction in the lobby, keep the faction human when a partner leaves, put everyone back on their faction when a shared save loads, make End Turn wait for every player, and let battle gifts work both ways so players can split an army. The Lua half ships the DLL inside the mod pack, writes it next to the game at boot, loads it, and handles the campaign side: version checks between players, a lobby status label, and logs.
Technical challenges
- No source, no API. Every behaviour change starts from reading the game's machine code. I locate targets by signature in non-writable code only, so a game update can't make a patch write somewhere random.
- Failing safely. If a signature stops matching after an update, that patch stays off and the lobby label says so. A game version that was never tested is allowed, but labelled as such.
- Testing without playing. A Python test disassembles a copy of the game with Capstone and checks every patch target, so a new game build can be vetted without launching it.
- Two PCs, one turn. Shared turns, battles and saves only show their bugs with two real machines, so that is how the mod was tested.
Outcome
Tested with two players on two PCs on game version 9.0.4, in Immortal Empires. The source is public under MIT, and the Steam Workshop release is being prepared.
