Netblocks

netblocks — multiplayer XR for XR Blocks

netblocks turns any XR Blocks app into a shared experience. Mental model: **a Transport

moves opaque bytes between peers; a NetSession layers presence, RPC, replicated objects, and

voice on top.** Swap transports without changing app code.

> Full reference (concepts, wire protocol, transports, security/threat model, samples):

> README.md. Samples: samples/SAMPLES.md.

When to use

Use netblocks for cooperative, trusted rooms — hack-day demos, co-located classrooms,

shared-screen moments. It is prototype-grade: ownership claims and events are cooperative,

transports don't authenticate peers, and there's no rate limiting. For adversarial settings

(anti-cheat, payments) terminate state at a server you control and treat netblocks as a

presence/transport veneer.

Quick start

import * as xb from 'xrblocks';
import {
  enableNet,
  BroadcastChannelTransport,
} from 'xrblocks/addons/netblocks/src/index.js';

class MyApp extends xb.Script {
  async init() {
    const net = enableNet(); // ticks on the standard xb frame loop
    const session = await net.joinRoom('my-room', {
      transport: new BroadcastChannelTransport(), // two tabs see each other instantly
      displayName: 'Alice',
    });
    session.events.on('chat', (text, fromPeerId) =>
      console.log(`${fromPeerId}: ${text}`)
    );
  }
}

xb.add(new MyApp());
xb.init();

Open the page in two tabs to see the other tab's head as a labeled avatar (plus hands in XR

with hand tracking).

Replicating an object

Wrap any Object3D in a NetObject and register it; owners broadcast, non-owners interpolate.

Ownership is cooperative — claim on grab, release on drop.

import {
  NetObject,
  WebRTCTransport,
} from 'xrblocks/addons/netblocks/src/index.js';

const sharedCube = new NetObject({id: 'cube', object: this.cube});
const net = enableNet();
await net.joinRoom('demo', {
  transport: new WebRTCTransport(),
  displayName: 'Alice',
});
net.session?.netObjects.add(sharedCube);
// session.claim(obj) on grab, session.release(obj) on drop.

Key surface

• enableNet() → NetCore (also xb.core.net); joinRoom(roomId, opts?), leaveRoom(),

send(topic, data). joinRoom defaults to WebRTCTransport when no transport is given.

• xb.core.net.peers — list(), remoteUsers, on('join'|'leave', cb), events.
• xb.core.net.user — local network identity (peerId, displayName, role). Distinct from

xb.user (the local XR input device).

• session.events — typed pub/sub: on(topic, cb), emit(topic, payload), emitTo(peerId, …).
• session.voice.enable() or joinRoom({voice: true}) — spatial WebRTC audio per peer head.

Transports

| Transport | Use for |

| --------------------------- | -------------------------------------------------------------------------------- |

| BroadcastChannelTransport | local dev — two tabs, zero infrastructure |

| WebRTCTransport | serverless P2P via PeerJS broker (≤ ~12 peers); pass iceServers/signalingUrl |

| WebSocketTransport | a small relay (server/relay.js) for reliable, scalable rooms |