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 0.19. 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 = "0.19"; 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). In 0.19 Resource extends Component, 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.