Lightyear

A library for writing server-authoritative multiplayer games with Bevy. Compatible with wasm via WebTransport.

Getting started

For Bevy 0.19, add Lightyear to your project with:

[dependencies]
lightyear = "0.29"

You can first check out the examples.

To quickly get started, you can follow this tutorial, which re-creates the simple_box example.

You can also find more information in this WIP book.

Repository layout

Workspace crate sources live under crates/, grouped by role. Directory names drop the lightyear_ prefix, but Cargo package names keep it.

• crates/io: low-level IO links and backends such as aeronet, link, udp, crossbeam, websocket, and webtransport
• crates/connection: connection abstractions and adapters such as connection, raw_connection, netcode, and steam
• crates/core: the top-level lightyear crate plus shared core, sync, utils, and frame interpolation crates
• crates/inputs: input crates such as inputs, inputs_native, input_bei, and inputs_leafwing
• crates/replication: replication, prediction, and interpolation crates
• crates/transport: serialization, transport, and message crates
• crates/integration: Bevy ecosystem integrations such as Avian
• crates/platform, crates/deterministic, crates/tools, and crates/tests: platform support, deterministic replication, tooling, and test support

Related projects

• lightyear-template: opiniated template for a bevy + lightyear starter project

Games

• Lumina
• cycles.io for bevy jam 5: https://cbournhonesque.itch.io/cyclesio

Features

• Transport-agnostic: Lightyear is compatible with a number of IO backends, including:
  • UDP sockets
  • Uses aeronet for WebSocket, Steam and WebTransport support
• Serialization
  • Lightyear uses postcard as a default serializer, but you can provide your own serialization function
• Message passing
  • Lightyear supports sending packets with different guarantees of ordering and reliability through the use of channels.
  • Packet fragmentation (for messages larger than ~1200 bytes) is supported
• Input handling
  • Lightyear has special handling for player inputs (mouse presses, keyboards). They are buffered every tick on the Client, and lightyear makes sure that the client input for tick N will be processed on tick N on the server. Inputs are protected against packet-loss: each packet will contain the client inputs for the last few frames.
  • With the leafwing feature, there is a special integration with the leafwing-input-manager crate, where your leafwing inputs are networked for you!
  • Also supports the bevy-enhanced-input crate!
• Deterministic replication
  • Lightyear supports deterministic replication when only inputs are replicated. The simulation needs to be deterministic. The deterministic replication is compatible with both lockstep and prediction/rollback.
• World Replication
  • lightyear uses bevy_replicon to enable world replication features (replication, interest management, pre-spawning, etc.)
• Advanced replication
  • Client-side prediction: with just a one-line change, you can enable client-prediction with rollback on the client, so that your inputs can feel responsive
  • Snapshot interpolation: with just a one-line change, you can enable Snapshot interpolation so that entities are smoothly interpolated even if replicated infrequently.
  • Input Delay: you can add a custom amount of input-delay as a trade-off between having a more responsive game or more miss-predictions
  • Bandwidth Management: you can set a cap to the bandwidth for the connection. Then messages will be sent in decreasing order of priority (that you can set yourself), with a priority-accumulation scheme
  • Lag Compensation is available so that predicted entities can interact with interpolated entities (used most often for fps games)
• Various topologies supported
  • You can run your app in client-server mode or in P2P mode. You can also have a client act as the server (host-client mode).
• Examples
  • Lightyear has plenty of examples demonstrating all these features, as well as the integration with other bevy crates such as avian

Supported bevy version

Lightyear	Bevy
0.28-0.29	0.19
0.26-0.27	0.18
0.25	0.17
0.20-0.24	0.16
0.18-0.19	0.15
0.16-0.17	0.14
0.10-0.15	0.13
0.1-0.9	0.12