bevy-ecs

Bevy ECS

Structure a Bevy game in Rust around the Entity Component System: the App and plugins, components and resources, systems with queries, scheduling, and frame-rate-independent updates. New examples target Bevy 0.20. If the project already pins another release, keep that release and use its matching migration guide.

When to use

• Use when wiring a Bevy App, defining Component/Resource types, writing systems that query entities, ordering/filtering systems, or fixing borrow-conflict panics and frame-dependent movement.
• Use when Cargo.toml depends on bevy and code calls App::new(), add_systems, Query, or Commands.

When not to use: this is the ECS core. Deep rendering, custom shaders/ pipelines, UI layout, and audio are separate concerns. For engine-agnostic AI or procedural algorithms, pair with game-ai / procedural-gen.

Core workflow

1. Detect and pin the version. Read Cargo.toml and Cargo.lock first. For a new project use bevy = "0.20"; never silently migrate an existing project across a Bevy minor release. Treat the matching docs and migration guides as truth.
2. Build the App. App::new().add_plugins(DefaultPlugins) gives windowing, input, rendering, time, etc. Register systems into schedules: Startup (once) and Update (every frame).
3. Model data as components, globals as resources. #[derive(Component)] for per-entity data; #[derive(Resource)] for one-of-a-kind data (score, settings, the Time clock). Since 0.19 Resource extends Component and each resource is stored on its own entity, so do not derive both.
4. Write systems as plain functions. Parameters declare data access: Query<...> for entities, Res<T>/ResMut<T> for resources, Commands for deferred spawn/despawn. Systems run in parallel when their accesses don't conflict.
5. Drive motion by time.delta_secs() so speed is frame-rate independent.
6. Order only what must be ordered with .chain() or explicit constraints; gate systems with run_if. Group related setup into Plugins. Build with cargo run and read the panics — Bevy reports conflicting queries at startup.