Multiplayer toy-car racing where phones become tilt controllers and a shared screen is the track.
A couch party game for 1–4 players on one shared screen — a TV, monitor, or laptop. Players join by scanning a QR code and tilt their phones to steer; empty seats fill with CPU racers, so every race runs a full grid. The display browser runs the authoritative 3D simulation; the Node.js server only serves static files and a QR-code endpoint.
The display browser is authoritative: it runs the race sim (Three.js) and broadcasts game state to every phone through a Party-Sockets WebSocket relay. Steering input rides a lower-latency WebRTC DataChannel (partyplug/PartyFastlane.js) when one is open, and falls back to the relay otherwise.
npm install
npm start # serves on http://localhost:4000- Open
http://localhost:4000on a big screen. - Players scan the QR code with their phones to join.
- The first player to join is the host and starts the race.
- Tilt to steer, hold BRAKE to slow down. First across the line wins.
Phones need HTTPS for the tilt sensors — front the server with a tunnel or TLS cert when testing on real devices.
| Input | Action |
|---|---|
| Tilt phone left/right | Steer |
| Hold BRAKE | Slow down |
| Tap USE (when lit) | Fire your power-up |
Cars auto-accelerate — tilt, brake, and USE are the only inputs. Drive over an item box to roll a power-up (a boost burst or a banana to drop behind you), which arms USE. Boost pads and rubber-banded item odds give trailing cars a catch-up edge.
public/
display/ # Authoritative sim (engine/Game.js) + Three.js renderer
controller/ # Phone tilt controller
shared/ # protocol.js — wire contract + relay/STUN config
server/ # Static-file + QR-code host (no game logic)
partyplug/ # Reusable party-game transport kit
Set the relay URL in public/shared/protocol.js (and the CSP connect-src in server/index.js if you self-host one). Server env vars:
| Variable | Default | Description |
|---|---|---|
PORT |
4000 |
HTTP server port |
BASE_URL |
Auto-detected LAN IP | Base URL for join links / QR codes |
APP_ENV |
development |
Set to production for production mode |
npm test # unit tests (node:test) — engine, tilt input, track, partyplug
npm run test:e2e # Playwright E2E against a hermetic relay stubUnit tests use Node's built-in node:test runner. The E2E suite (tests/e2e/) drives the real display and controller pages against a local relay stub, so no production relay is needed (run npx playwright install chromium once). /gallery.html is a manual no-relay preview surface for UI checks.
Vanilla JavaScript + ES modules, no build step. Three.js (vendored) renders the Kenney Toy Car Kit. Transport is the Party-Sockets WebSocket relay plus WebRTC DataChannels for low-latency input. One production dependency (qrcode).