bevy_gaff (work in progress)

bevy_gaff is an attempt at making a networked (p2p), cross-platform physics simulation using rollback netcode.

It synchronizes only user input and relies on determinism for the simulation to stay in sync.

It also serves as kind of a showcase/demo of the following rust gamedev crates:

• Bevy: game engine
• GGRS: rollback netcode
• bevy_xpbd: physics engine
• Matchbox: p2p networking

On network delays physics state is predicted ahead of time, assuming other players input will stay the same as the last frame. If conflicting input is received later, an older state is restored, and the physics simulation is replayed using the updated input.

This means the simulation stays responsive, and you will always see the result of your own input immediately regardless of ping to other players.

Input is also sent directly between players (p2p, no intermediate server) even when running on WASM, this means that if the players are located closely, mis-predictions will be rare and the latency barely noticeable.

Running it

Install and run matchbox_server

cargo install matchbox_server
matchbox_server

...and run two instances of the "game":

cargo run

The example can also be run "single-player":

cargo run -- --players 1

Or with any other number of players

Issues

• simulation occasionally desyncs on rollbacks locally

Relevant links

• Gaffer On Games - Introduction to networked physics
• bitshifter/glam-rs#388