OpenXcomWASM

Play OpenXcom in your browser. The full C++ engine compiled to WebAssembly — no plugins, no install, works offline after first visit.

Play online: playxcom.online

Powered by: OpenXcom fork (SDL2, Emscripten patches)

Features

• Full OpenXcom engine running natively in the browser via WebAssembly
• Game data and saves stored locally in IndexedDB (nothing leaves your machine)
• Persistent saves across browser sessions
• Export/import saves as .zip or .sav for backup or cross-device transfer
• Service worker for offline play after first visit
• Landing page with getting-started guide

Quick start

# Clone with submodules (pulls the OpenXcom fork automatically)
git clone --recursive https://github.com/mrmrcoleman/OpenXcomWASM.git
cd OpenXcomWASM

# Install Emscripten SDK
# https://emscripten.org/docs/getting_started/downloads.html
# Ensure emcmake and emmake are on PATH

# Build
./scripts/build-wasm.sh

# Serve locally
./scripts/serve.sh
# Open http://localhost:8080

Repo layout

OpenXcomWASM/
  OpenXcom/          Git submodule — the patched OpenXcom fork
  scripts/
    build-wasm.sh    Build the WASM binary
    build-desktop.sh Build native binary (for testing)
    serve.sh         Local dev server (copies web assets + serves dist/)
    deploy-gh-pages.sh  Deploy to GitHub Pages
  web/
    index.html       Landing page
    play.html        Game page (HTML shell for Emscripten)
    sw.js            Service worker for offline caching
    jszip.min.js     JSZip library (bundled for offline support)
  dist/              Build output (WASM artifacts + web assets)

Building

Prerequisites

• Emscripten SDK with emcmake and emmake on PATH
• CMake 3.14+

WASM build

./scripts/build-wasm.sh

Output goes to dist/. The build script automatically pulls the OpenXcom submodule if needed.

To preload game data into the build (for development only):

GAME_DATA=/path/to/UFO ./scripts/build-wasm.sh

Desktop build (for testing)

brew install cmake sdl2 sdl2_mixer sdl2_image sdl2_gfx yaml-cpp   # macOS
./scripts/build-desktop.sh

Deployment

Pushes to main trigger a GitHub Actions workflow (.github/workflows/deploy.yml) that builds the WASM binary and deploys to GitHub Pages. WASM build artifacts are cached, so web-only changes deploy in about a minute. The service worker's cache version is automatically stamped with the commit SHA for cache busting.

To use a custom domain, set the CUSTOM_DOMAIN repository variable in GitHub (Settings > Variables > Actions). The workflow writes a CNAME file to the deploy output automatically.

How it works

The OpenXcom C++ engine is compiled to WebAssembly using Emscripten. Static game data (common/standard resources) is preloaded into the WASM virtual filesystem. User-provided game data (the UFO/ directory from a legitimate copy of X-COM) is uploaded once and persisted in IndexedDB via Emscripten's IDBFS. Saves are synced to IndexedDB every 30 seconds during gameplay.

A service worker caches all static assets after first load, enabling full offline play.

License

GPL v3 — same as OpenXcom.

X-COM: UFO Defense is copyright Mythos Games / MicroProse. You need a legitimate copy of the game data to play.