Crate bevy_save

Bevy_save

A framework for saving and loading game state in Bevy.

https://user-images.githubusercontent.com/29737477/234151375-4c561c53-a8f4-4bfe-a5e7-b69af883bf65.mp4

Features

Save file management

bevy_save automatically uses your app’s workspace name to create a unique, permanent save location in the correct place for whatever platform it is running on.

• World::save() and World::load() uses your app’s save location to save and load your game state, handling all serialization and deserialization for you.
• These methods accept a Pipeline, a strongly typed representation of how you are going to be saving and loading.
• The Pipeline trait uses the Backend trait as an interface between disk / database and bevy_save.
• The Backend trait uses the Format trait to determine what format should be used in the actual save files (MessagePack / RON / JSON / etc)
  • The default Pipeline uses the FileIO backend which saves each snapshot to an individual file on the disk by the given key.
    • Many games have different requirements like saving to multiple directories, to a database, or to WebStorage.
    • You can use a different Backend by implementing your own Pipeline with a custom Backend.
  • The default Pipeline is set up to use rmp_serde as the file format.
    • You can use to a different Format by implementing your own Pipeline with a custom Format.

Save directory location

With the default FileIO backend, your save directory is managed for you.

WORKSPACE is the name of your project’s workspace (parent folder) name.

Windows	Linux/*BSD	MacOS
C:\Users\%USERNAME%\AppData\Local\WORKSPACE\saves	~/.local/share/WORKSPACE/saves	~/Library/Application Support/WORKSPACE/saves

On WASM, snapshots are saved to LocalStorage, with the key:

WORKSPACE.KEY

Snapshots and Rollback

bevy_save is not just about save files, it is about total control over game state.

This crate introduces a snapshot type which may be used directly:

• Snapshot is a serializable snapshot of all saveable resources, entities, and components.

Or via the World extension methods:

• World::snapshot() captures a snapshot of the current game state, including resources.
• World::checkpoint() captures a snapshot for later rollback / rollforward.
• World::rollback() rolls the game state backwards or forwards through any checkpoints you have created.

The Rollbacks resource also gives you fine-tuned control of the currently stored rollbacks.

Type registration

bevy_save adds methods to Bevy’s App for registering types that should be saved. As long as the type implements Reflect, it can be registered and used with bevy_save.

• App.init_pipeline::<P>() initializes a Pipeline for use with save / load.
• App.allow_rollback::<T>() allows a type to roll back.
• App.deny_rollback::<T>() denies a type from rolling back.

Type filtering

bevy_save allows you to explicitly filter types when creating a snapshot.

Entity mapping

As Entity ids are not intended to be used as unique identifiers, bevy_save supports mapping Entity ids.

First, you’ll need to get a SnapshotApplier:

• Snapshot::applier()
• SnapshotApplier::new()

The SnapshotApplier will then allow you to configure the entity map (and other settings) before applying:

let snapshot = Snapshot::from_world(world);

snapshot
    .applier(world)

    // Your entity map
    .entity_map(HashMap::default())

    // Despawn all entities matching (With<A>, Without<B>)
    .despawn::<(With<A>, Without<B>)>()

    .apply();

MapEntities

bevy_save also supports MapEntities via reflection to allow you to update entity ids within components and resources.

See Bevy’s Parent Component for a simple example.

Entity hooks

You are also able to add hooks when applying snapshots, similar to bevy-scene-hook.

This can be used for many things, like spawning the snapshot as a child of an entity:

let snapshot = Snapshot::from_world(world);

snapshot
    .applier(world)

    // This will be run for every Entity in the snapshot
    // It runs after the Entity's Components are loaded
    .hook(move |entity, cmds| {
        // You can use the hook to add, get, or remove Components
        if !entity.contains::<Parent>() {
            cmds.set_parent(parent);
        }
    })

    .apply();

Hooks may also despawn entities:

let snapshot = Snapshot::from_world(world);

snapshot
    .applier(world)

    .hook(|entity, cmds| {
        if entity.contains::<A>() {
            cmds.despawn();
        }
    })

Partial Snapshots

While bevy_save aims to make it as easy as possible to save your entire world, some games also need to be able to save only parts of the world.

Builder allows you to manually create snapshots like DynamicSceneBuilder:

fn build_snapshot(world: &World, target: Entity, children: Query<&Children>) -> Snapshot {
    Snapshot::builder(world)
        // Extract all resources
        .extract_all_resources()

        // Extract all descendants of `target`
        // This will include all components not denied by the builder's filter
        .extract_entities(children.iter_descendants(target))

        // Entities without any components will also be extracted
        // You can use `clear_empty` to remove them
        .clear_empty()

        // Build the `Snapshot`
        .build()
}

You are also able to extract resources by type:

Snapshot::builder(world)
    // Extract the resource by the type name
    // In this case, we extract the resource from the `manual` example
    .extract_resource::<FancyMap>()

    // Build the `Snapshot`
    // It will only contain the one resource we extracted
    .build()

Additionally, explicit type filtering like Applier is available when building snapshots:

Snapshot::builder(world)
    // Exclude `Transform` from this `Snapshot`
    .deny::<Transform>()

    // Extract all matching entities and resources
    .extract_all()

    // Clear all extracted entities without any components
    .clear_empty()

    // Build the `Snapshot`
    .build()

Pipeline

Pipelines allow you to use multiple different configurations of Backend and Format in the same App.

Pipelines also let you re-use Snapshot appliers and extractors.

License

bevy_save is dual-licensed under MIT and Apache-2.0.

Feature Flags

Feature flag	Description	Default?
bevy_asset	Enables bevy_asset type registration	Yes
bevy_render	Enables bevy_render type registration	Yes
bevy_sprite	Enables bevy_sprite type registration	Yes
brotli	Enables Brotli compression middleware	No

Compatibility

Bevy

NOTE: We do not track Bevy main.

Bevy Version	Crate Version
0.12	0.10, 0.11, 0.12, 0.13
0.11	0.9
0.10	0.4, 0.5, 0.6, 0.7, 0.8
0.9	0.1, 0.2, 0.3

Platforms

Platform	Support
Windows	:heavy_check_mark:
MacOS	:heavy_check_mark:
Linux	:heavy_check_mark:
WASM	:heavy_check_mark:
Android	:question:
iOS	:question:

:heavy_check_mark: = First Class Support — :ok: = Best Effort Support — :zap: = Untested, but should work — :question: = Untested, probably won’t work — :hammer_and_wrench: = In progress

Modules

• prelude
  Prelude: convenient import for all the user-facing APIs provided by the crate

Structs

• DebugPipeline
  Uses JSON and saves to the given local path.
• FileIO
  Simple filesystem backend.
• JSONFormat
  An implementation of Format that uses serde_json.
• RMPFormat
  An implementation of Format that uses rmp_serde.
• RollbackRegistry
  The global registry of types that should be included in Rollbacks.
• Rollbacks
  The global registry of snapshots used for rollback / rollforward.
• RollbacksDeserializer
  Handles rollbacks deserialization.
• RollbacksSerializer
  Handles serialization of the global rollbacks store.
• SAVE_DIR
  The platform-specific save directory for the app.
• SavePlugin
  bevy_save core functionality.
• SavePlugins
  Default plugins for bevy_save.
• SaveablesPlugin
  Saveable registrations for common types.
• Snapshot
  A collection of serializable entities and resources.
• SnapshotApplier
  SnapshotApplier lets you configure how a snapshot will be applied to the [World].
• SnapshotBuilder
  A snapshot builder that can extract entities, resources, and Rollbacks from a [World].
• SnapshotDeserializer
  Handles snapshot deserialization.
• SnapshotSerializer
  Handles serialization of a snapshot as a struct containing its entities and resources.

Enums

• Error
  An error that may occur when loading saves or rollbacks.

Constants

• WORKSPACE
  The name of the project’s workspace.

Traits

• AppSaveableExt
  Extension trait that adds save-related methods to Bevy’s [App].
• Backend
  Interface between the Format and the disk or other storage.
• CloneReflect
  Clone-like trait for duplicating [Reflect]-related types.
• Format
  Handles serialization and deserialization of save data.
• Hook
  A Hook runs on each entity when applying a snapshot.
• Pipeline
  Trait that defines how exactly your app saves and loads.
• WorldRollbackExt
  Extension trait that adds rollback-related methods to Bevy’s [World].
• WorldSaveableExt
  Extension trait that adds save-related methods to Bevy’s [World].

Functions

• get_save_file
  Returns the absolute path to a save file given its name.

Type Aliases

• BoxedHook
  A boxed Hook.
• DefaultBackend
  The Backend the default Pipeline will use.
• DefaultDebugBackend
  The Backend the default debug Pipeline will use.
• DefaultDebugFormat
  The Format the default Pipeline will use.
• DefaultFormat
  The Format the default Pipeline will use.