# Engine source (GPL-2.0)

The game engine in this directory (`websockets-doom.js`, `websockets-doom.wasm`)
is **doom-wasm**, Cloudflare's WebAssembly port of Chocolate Doom, built with
small local changes. It is free software under the GNU General Public License,
version 2; the full text is in [`COPYING`](COPYING). This file is our offer of
the complete corresponding source.

## Upstream

- Repository: <https://github.com/cloudflare/doom-wasm>
- Commit: `65e0d3ae2ffa604155eebd96ed40da6567bd08f4`
  ("Adding semgrep yaml file", 2024-09-19)
- Based on Chocolate Doom: <https://github.com/chocolate-doom/chocolate-doom>

## Local changes

One patch, [`source/doom-wasm-worduelus.patch`](source/doom-wasm-worduelus.patch),
applied with `git apply` on top of the commit above:

1. `configure.ac` — build flags updated for current Emscripten: compile as
   `-std=gnu11`; drop the source map, `SAFE_HEAP` and stack checks; replace the
   removed `EXTRA_EXPORTED_RUNTIME_METHODS` with `EXPORTED_RUNTIME_METHODS`
   (`FS`, `callMain`, `ccall`); allow memory growth; do not run `main`
   automatically (the page calls it after the player clicks); link IDBFS so
   config and savegames persist in IndexedDB.
2. `opl/opl.c` — `OPL_Delay` waited on an SDL condition variable, which
   deadlocks in a build without threads. Under Emscripten it now yields with
   `emscripten_sleep(1)` until the OPL timer fires, so OPL (FM synth) music
   works instead of hanging at startup.
3. `src/doom/g_game.c` — Ctrl fires in addition to the configured fire key.

The engine is used single player only. Its WebSocket netplay code is still
compiled in but is only reached with `-connect`/`-server`/`-wss` arguments,
which the page never passes, so it makes no network connections.

## Build

Toolchain: Docker image `emscripten/emsdk:3.1.51`
(`emscripten/emsdk@sha256:fde95518821ccc1b629ee674a7a068a809fda47ea16814b0ed53bd646555147b`,
emcc 3.1.51 `c0c2ca1314672a25699846b4663701bcb6f69cca`). Host autotools
(autoconf/automake) generate `configure`, since the image does not ship them.

Note: emsdk 6.0.10 also builds this tree, but the result is broken at run time
(status bar garbage, wrong lighting, missing weapon sprite), so use 3.1.51.

```sh
git clone https://github.com/cloudflare/doom-wasm.git
cd doom-wasm
git checkout 65e0d3ae2ffa604155eebd96ed40da6567bd08f4
git apply /path/to/source/doom-wasm-worduelus.patch
autoreconf -fiv                      # on the host
cd ..
cp /path/to/source/build-in-emsdk.sh build.sh
docker run --rm --network host -u "$(id -u):$(id -g)" \
  -v "$PWD:/work" -w /work emscripten/emsdk:3.1.51 ./build.sh
# -> doom-wasm/src/websockets-doom.js and websockets-doom.wasm
```

[`source/build-in-emsdk.sh`](source/build-in-emsdk.sh) fetches the SDL2,
SDL2_mixer and SDL2_net Emscripten ports, then runs:

```sh
CFLAGS="-g0" ac_cv_exeext=".html" emconfigure ./configure \
  --host=none-none-none --without-libpng --without-libsamplerate
emmake make -j20
```

The page around the engine (`index.html`, `harness.js`, `harness.css`,
`default.cfg`, `chocolate-doom.cfg`) is ours and is not part of the engine.