Open Source DOOM

Real-time P2P multiplayer DOOM. No servers required.
A 4.2MB file in a chat message. Open it. Frag your friends.

Blog Post · Download Vector · Releases

---

What is this?

Open Source DOOM is a fork of Cloudflare's doom-wasm (Chocolate Doom compiled to WebAssembly) with the entire networking stack rebuilt from scratch for real-time, decentralised, peer-to-peer multiplayer over WebXDC realtime channels.

It ships as a .xdc file - a tiny zip archive you send in a chat message. No servers, no accounts, no app stores. Your friend opens it, and you're playing DOOM together.

What changed from Cloudflare's version?

	Cloudflare	Open Source DOOM
Transport	WebSockets via Cloudflare Edge	P2P gossip via Iroh (QUIC)
Server	Durable Object (centralised)	Auto-elected from players
Sync model	Lockstep (1993 original)	Real-time hybrid (snapshots + interpolation)
Damage	Simulated locally by all clients	Host-authoritative events
NPCs	Simulated locally by all clients	Host-authoritative snapshots
Late join	Not supported	Fully supported
Internet	Required (Cloudflare Workers)	Not required (P2P)
Delivery	Website	4.2MB chat message

For the full technical deep-dive, read the blog post.

Key features

• No servers - Magic-byte server election picks a host automatically in ~3 seconds
• Real-time gameplay - Position snapshots every 57ms with exponential smoothing interpolation
• Host authority - Health, damage, NPCs, USE events, and respawns are host-authoritative
• NPC synchronisation - Monsters are simulated only on the host, snapshots drive all clients
• Mid-game joining - Drop in anytime with tic synchronisation
• Mobile touch controls - Dual joysticks, action buttons, weapon cycling
• Gamepad support - Web Gamepad API with analog sticks, triggers, and d-pad
• Co-op and Deathmatch - Both game modes supported
• 4.2MB total - Engine + shareware WAD + UI, compressed with zip -9

Play it

The easiest way to play is through Vector:

1. Open Vector
2. Go to Vector Nexus (the in-app Mini App store)
3. Find DOOM in the Multiplayer category
4. Send it to a friend or group chat
5. Both open it - game on

It also works in Delta Chat and any other WebXDC-compatible messenger.

Build from source

Prerequisites

• Emscripten SDK (tested with 5.0.2)
• autotools (automake, autoconf)
• SDL2 libraries

Compile

# Set up emsdk
cd /tmp && git clone https://github.com/emscripten-core/emsdk.git
cd emsdk && ./emsdk install 5.0.2 && ./emsdk activate 5.0.2

# Configure
export PATH="/tmp/emsdk:/tmp/emsdk/upstream/emscripten:$PATH"
emconfigure autoreconf -fiv
ac_cv_exeext=".html" emconfigure ./configure --host=none-none-none
emmake make -j4

Package as .xdc

# Requires doom1.wad (shareware) in src/
./build-xdc.sh
# Output: vectordoom.xdc (~4.2MB)

Architecture

index.html          UI, touch controls, gamepad, CRT theme
webxdc-net.js       Server election + packet routing (--pre-js)
vector-doom.wasm    Chocolate Doom engine (Emscripten)
  net_webxdc.c        WebXDC transport module
  d_net.c             Snapshot interpolation, health/damage authority
  p_netsync.c/h       NPC net ID registry + snapshot sync
  net_client.c        Custom packet sending (damage, USE, respawn, chat)
  net_server.c        Custom packet routing + late join handling
  i_input.c           JS input injection (inject_key_event, inject_mouse_motion)

See CLAUDE.md for the full technical reference and NETCODE_ARCHITECTURE.md for the deep-dive on tic synchronisation.

Credits

• id Software - Open-sourcing the DOOM engine (1997)
• Chocolate Doom - Faithful portable DOOM recreation
• Cloudflare - doom-wasm port (the foundation we forked)
• Emscripten - C to WebAssembly compiler
• Iroh - QUIC-based P2P gossip protocol
• WebXDC - Open standard for sandboxed chat apps

License

GNU GPL-2.0 (inherited from Chocolate Doom / id Software)