bevy_roll_safe

Rollback-safe implementations and utilities for Bevy Engine.

Motivation

Some of Bevy's features can't be used in a rollback context (with crates such as bevy_ggrs). This is either because they behave non-deterministically, rely on inaccessible local system state, or are tightly coupled to the Main schedule.

Roadmap

• States
  • Basic freely mutable states
  • OnEnter/OnLeave/OnTransition
• FrameCount
• Rollback-safe "Main"/default schedules
• Audio playback
  • Support all PlaybackModes
  • Support for seeking in "time-critical" audio
  • Support for formats that don't report sound durations (mp3/ogg)
• Events

States

Bevy states when added through app.init_state::<FooState>() have two big problems:

1. They happen in the StateTransition schedule within the MainSchedule
2. If rolled back to the first frame, OnEnter(InitialState) is not re-run.

This crate provides an extension method, init_roll_state_in_schedule::<S>(schedule), which lets you add a state to the schedule you want, and a resource, InitialStateEntered<S> which can be rolled back and tracks whether the initial OnEnter should be run (or re-run on rollbacks to the initial frame).

If you are using the rollback schedule plugin as well. Adding a rollback safe state is a simple as app.init_roll_state::<YourState>().

See the states example for usage with bevy_ggrs.

Default rollback schedule

RollbackSchedulePlugin adds rollback-specific alternatives to the schedules in Bevy's FixedMain/Main schedules.

The plugin takes a parent schedule as input, so it can easily be added to the ggrs schedule or any other schedule you want.

Rollback audio

RollbackAudioPlugin lets you easily play sound effects from a rollback world without duplicate sounds playing over each other. It depends on the RollbackSchedulePlugin, or you need to add the maintenance system in a similar order to your own schedules.

Cargo features

• audio: Enable rollback-safe wrapper for bevy_audio
• bevy_ggrs: Enable integration with bevy_ggrs
• math_determinism: Enable cross-platform determinism for operations on Bevy's (glam) math types.

Bevy Version Support

License

bevy_roll_safe is dual-licensed under either

• MIT License (./LICENSE-MIT or http://opensource.org/licenses/MIT)
• Apache License, Version 2.0 (./LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

at your option.

Contributions

PRs welcome!