reo: Resident Evil Outbreak, recompiled

A static recompilation of Resident Evil Outbreak (PS2, NTSC-U SLUS-20765) to native Windows x86-64 code, built on PS2Recomp. You supply your own disc; the recompiler turns its code into C++ on your machine, and that is built against PS2Recomp's runtime.

Fan project, not affiliated with Capcom or Sony. The repo contains no game code or data. Generated source is not distributed: you run the recompiler locally and its output lands in the gitignored recomp/config/output*/ folders.

Status

Alpha. A scripted boot reaches gameplay: the first scenario opens in J's Bar, drawn by the game's own code. It runs far below full speed, and nothing past that point has been tried. No release has been tagged.

The game runs its own recompiled code with no injected state. Its own IOP modules (CRI ADX/DTX, Capcom's sound driver, USB, the pad and memory-card drivers) run on PS2Recomp's IOP interpreter. With a pad script (PS2X_PAD_SCRIPT, guest-timed) a headless run goes through the boot splashes, the Capcom logo and title movie, the menus (single play, scenario, character, difficulty), the intro movie and NOW LOADING into the scenario. Every wall so far, and how each was found, is in docs/boot-gates.md.

Stage	State
ELF load, ~3,700 recompiled functions	works
All nine overlays recompiled, dispatched by which one is resident	works
Kernel threads, semaphores, interrupt handlers	works
SIF RPC, IOP heap, LOADFILE	works
Game's IRX modules on the IOP interpreter	works
CDVD file lookup and reads, CRI file server (ADXF)	works
Pad (DualShock 2 behind sio2man)	works
Memory card	no card: the game's "continue without saving" path works; a card image does not mount yet
Boot splashes, title screen, menus	works; the title background is missing
FMV (IPU, Play!'s decoder)	plays; motion-compensated frames show green blocks
Loading into the first scenario	works
In-game 3D (VU1 + GS)	draws; about 35x slower than real time
Playing the scenario	not tried yet
Sound output (SPU2)	not implemented
File #2 (SLUS-20984)	builds; no boot work
Online play	out of scope for now

Screenshots

A scripted headless run of the current build (2026-10-19), from its own frame dumps (PS2X_FRAME_DUMP, one frame every 10 vsyncs). It shows the boot splashes, the menus up to character select, and the first scenario in J's Bar. The FMVs and the loading screen are cut. The green behind the menus is the missing title background. The bar is reached after about 2.5 minutes of host time. From there it is about 35 times slower than real time: the 27 seconds of game time in the bar took about 16 minutes. The GIF plays at 10 fps, so it runs about 1.7 times faster than the game would.

Getting Started

You need your own copy of Resident Evil Outbreak, NTSC-U (SLUS-20765): the disc in a drive, or the disc's files copied to a folder (the folder that holds SLUS_207.65 and BIN\).

Quick start

1. Download this repo (Code → Download ZIP, or clone it) and unzip it somewhere with ~15 GB free.
2. Double-click Setup.cmd.
3. It checks for Git, Visual Studio 2022, CMake and Python, and tells you what's missing and where to get it (it never installs anything by itself).
4. It finds the game disc, or asks for the folder, and copies the files into game_data\.
5. It builds PS2Recomp, recompiles the game, and builds reo_recomp.exe. The last build takes 20-40 minutes.
6. Double-click run-reo.cmd.

If it stops, it prints one sentence on what to do and keeps the details in scratch\setup.log. Running it again carries on from the step that failed.

Setup.cmd --check only checks the prerequisites.

Step by step

Prerequisites, tested versions in brackets:

• Windows 10/11 x64
• Visual Studio 2022 with "Desktop development with C++" [17.x]
• CMake ≥ 3.20 [4.2.1]
• Python 3 with the py launcher [3.13]
• Git
• ~2 GB of RAM per parallel compiler job (8 jobs by default; -DREO_COMPILE_JOBS=4 for less)

Run everything from the repo root in Git Bash (or adapt the slashes for cmd).

1. Fetch the toolkit:

   git submodule update --init --recursive
   

2. Copy your disc's files into game_data/ so that game_data/SLUS_207.65 and game_data/BIN/0.DAT exist.
3. Configure and build PS2Recomp (the first configure downloads its libraries):

   cmake -S third_party/PS2Recomp -B third_party/PS2Recomp/out/build-upstream \
         -G "Visual Studio 17 2022" -A x64 -DPS2X_BUILD_STUDIO=OFF -DPS2X_ENABLE_FFMPEG=OFF
   cmake --build third_party/PS2Recomp/out/build-upstream --config Release \
         --target ps2_runtime ps2_iop ps2_recomp
   

   Keep PS2X_ENABLE_FFMPEG=OFF: ON links shared FFmpeg and the exe then needs its DLLs.
4. Recompile the game ELF and its nine overlays. gen_base_config.py writes recomp/build/outbreak.generated.toml: outbreak.toml plus the base-ELF functions the overlays call, read from your BIN/*.DAT.

   py -3 tools/gen_base_config.py
   ./third_party/PS2Recomp/out/build-upstream/ps2xRecomp/Release/ps2_recomp.exe recomp/build/outbreak.generated.toml
   for o in 0:submain 1:demo 2:game 3:netwk 4:netdnas 5:insdnas 6:nethttp 8:netaq 9:single; do
     py -3 tools/gen_overlay.py game_data/BIN/${o%%:*}.DAT ${o##*:}
   done
   

5. Configure and build the game:

   cmake -S recomp -B recomp/build -G "Visual Studio 17 2022" -A x64
   cmake --build recomp/build --config Release --target reo_recomp
   

6. Run it:

   ./recomp/build/Release/reo_recomp.exe --game file1
   

   Expected: the banner, then [BOOT] lines ([BOOT] overlay: loaded netdnas.bin at 0x006E0000, [BOOT] Registering overlay functions ...) and the runtime's log. A window opens showing the GS framebuffer.

Trip-ups:

• python opens the Microsoft Store. That's the Store alias; use py -3, or turn the alias off in Settings → Apps → Advanced app settings → App execution aliases.
• A tool "isn't found" right after installing it. Open a new terminal so PATH updates.
• Edits under third_party/PS2Recomp/ps2xRuntime do nothing. The game links the runtime as a prebuilt .lib; rebuild step 3 before step 5.
• Link errors on entry_* symbols after regenerating. Re-run the configure in step 5; it globs the generated files.

Usage

reo_recomp.exe [--game file1|file2] [--elf <path>] [--data <path>]

--data defaults to game_data (File #2: game_data_file2), --elf to <data>/SLUS_207.65.

Run without a window (over RDP, with the monitor asleep, in scripts):

REO_HEADLESS=1 ./recomp/build/Release/reo_recomp.exe --game file1

Debugging switches are environment variables, all off by default. The most useful:

PS2X_WATCH_WRITE=0x29F708     # who writes this guest word (pc, ra, sp of every store)
PS2X_TRACE_RANGE=0x6e0000:0x751000   # is anything in this range ever entered?
PS2X_TRACE_SYNC=1             # threads, semaphores, RPC binds and calls
PS2X_TRACE_IRQ=1              # interrupt dispatches and DMA kicks

The full list and the method that has found every boot wall so far: docs/debugging.md.

Building from source

Steps 3-5 above are the whole build. Two things to know (more in docs/architecture.md):

• The toolkit and the game are separate CMake trees. Rebuild the toolkit first after any change under third_party/PS2Recomp.
• PS2Recomp's own test suite: cmake --build third_party/PS2Recomp/out/build-upstream --config Release --target ps2x_tests, then ./third_party/PS2Recomp/out/build-upstream/ps2xTest/Release/ps2x_tests.exe.

src/, most of runtime/ and network/ are an early hand-written hardware layer that is not used by the running game; see the architecture doc.

Documentation

• docs/architecture.md: the parts, the two build trees, data flow
• docs/boot-gates.md: every boot wall, its cause and fix; the current wall
• docs/debugging.md: trace switches and method
• docs/mwo3-overlay-format.md: the overlay container format
• ROADMAP.md, CHANGELOG.md

References

• PS2Recomp: the recompiler and runtime (GPL-3.0)
• PS2Tek: PS2 hardware documentation
• Outbreak Research: file format documentation
• PCSX2 is used as a black box to compare against: GS dumps and guest memory captures

Contributors

See CONTRIBUTING.md. Codegen fixes in the PS2Recomp fork this project first tracked (VU0 dest-mask, FPU divide-by-zero, 64-bit branches) came from @jlsandri; most have since landed upstream.

License

GPL-3.0 (see LICENSE). reo links PS2Recomp's GPL-3.0 runtime, so the combined program is GPL. Third-party code and its licences are listed in NOTICE.

Resident Evil is a trademark of Capcom. PlayStation is a trademark of Sony Interactive Entertainment.