TH08-Platform

Private. Touhou 8 — Imperishable Night — co-op multiplayer platform via DLL injection into the original game binary.

What this is

Two tracks bundled in one monorepo:

1. game/ — th08 decomp (fork of GensokyoClub/th08, AGPL-3.0). Source-level reconstruction of th08 v1.00d used as a knowledge base for struct layouts and function addresses. Currently ~55% byte-matched.

2. dll/ — multiplayer DLL + loader. Hooks into the original th08.exe at runtime via MinHook; adds UDP rollback netcode and a second player. The original binary is never modified on disk — only injected into memory at process start via th08_platform_loader.exe.

The platform goal: a lobby/matchmaking service where two players launch, get matched, and the DLL handles synchronized gameplay.

Status — 2026-04-25

Area	State
Decomp (bytes matching original)	~55% (399+ of 722 tracked functions)
DLL Phase 0 (proof-of-injection hook)	scaffold ready, not yet built
DLL Phase 1-5 (state capture, netcode, P2)	planned in docs/DLL_PLAN.md
Platform / lobby UI	not started

Repo layout

TH08-Platform/
├── README.md
├── .gitignore                          excludes th08.exe + build artifacts
│
├── game/                               th08 decomp (fork of GensokyoClub/th08)
│   ├── src/                            game source reconstructed in C++
│   ├── config/                         mapping.csv, reccmp symbols, etc.
│   ├── scripts/                        VS2002 + DX8 build system
│   ├── objdiff.json                    objdiff config
│   ├── reccmp-project.yml              reccmp project config
│   └── LICENSE                         AGPL-3.0 (inherited upstream)
│
├── dll/                                multiplayer DLL (new)
│   ├── CMakeLists.txt                  FetchContent pulls MinHook
│   ├── src/
│   │   ├── main.cpp                    DllMain
│   │   ├── logging.{h,cpp}             logs to %LOCALAPPDATA%\th08_platform\log.txt
│   │   └── hooks/game_loop.{h,cpp}     Phase 0: hook GameManager::OnUpdate @ 0x43aa03
│   └── loader/loader.cpp               injector exe
│
├── tools/                              decomp factory helpers
│   ├── ida_helper.py                   IDA MCP HTTP client
│   ├── batch_analyze[_v2..v5].py       pre-analyzers that emit worksheets
│   └── copy_to_monorepo.py             snapshot th08-decomp → this repo
│
└── docs/
    ├── DLL_PLAN.md                     architecture + 6-phase roadmap
    └── worksheets/                     pre-analysis worksheets used by codex batches

Prerequisites

• th08.exe v1.00d — SHA256 330fbdbf58a710829d65277b4f312cfbb38d5448b3df523e79350b879213d924. You supply this; it is not in the repo (copyrighted by ZUN / Team Shanghai Alice).
• Python 3.12+ (for build scripts and factory tools)
• Git, CMake 3.20+
• Visual Studio 2022 (for DLL build) — 32-bit target required
• IDA Pro 9.x with ida-pro-mcp plugin (only needed to run the decomp factory)
• reccmp — pip install reccmp (only for running diff against original)

Build — game decomp (the C++ that should match th08.exe byte-for-byte)

cd game
cp /your/th08.exe resources/th08.exe
python scripts/create_devenv.py scripts/dls scripts/prefix   # first time only, ~10 min
python scripts/build.py                                       # produces build/th08.exe

Verify how close we are to byte-matching:

cd build
reccmp-reccmp --target th08 --json ../diff_report.json
# check % per-function in diff_report.json

Build — DLL (Phase 0 hello-world)

cd dll
cmake -B build -A Win32
cmake --build build --config Release
# outputs: build/bin/th08_platform.dll and th08_platform_loader.exe

Run — inject DLL into your own th08.exe

dll/build/bin/th08_platform_loader.exe /path/to/your/th08.exe
# then tail %LOCALAPPDATA%\th08_platform\log.txt to see frame counter ticking

Roadmap

Six phases detailed in docs/DLL_PLAN.md. Summary:

• Phase 0 — hello DLL, hooks GameManager::OnUpdate, logs frames (current scaffold)
• Phase 1 — state capture / restore (rollback foundation)
• Phase 2 — input hook (merge local + remote)
• Phase 3 — UDP lockstep netcode
• Phase 4 — rollback netcode (~Giuroll level)
• Phase 5 — second player ship + shared HUD
• Phase 6 — external lobby / matchmaking service

Credits

• GensokyoClub/th06 + GensokyoClub/th08 — the decomp foundation
• Giuroll — rollback netcode reference (Soku / th12.3)
• th06_multi_net — proof that multiplayer via decomp is achievable
• reccmp, MinHook, Dear ImGui — the tooling we lean on

License

AGPL-3.0-or-later, inherited from game/ upstream. Private repo: no distribution of modified game binaries. Users must supply their own th08.exe.