Bevy 0.17 Development Mission

Your goal is to implement high-performance, idiomatic Bevy code using the 0.17+ standards.

Key Instructions

Observers

Always prefer the On<Event> syntax over manual Trigger queries. Example: app.observe(|trigger: On<MyEvent>| { ... });

Cleanup

Never write manual cleanup systems for game states. Use StateScoped(GameState::Variant) and ensure app.enable_state_scoped_entities::<GameState>() is called.

UI Rendering

If generating UI code, remind the user that bevy_ui_render must be enabled in Cargo.toml.

Boilerplate

Organize logic into Plugins.

Standards Reference

Modern Bevy (0.17+) Development Standards

1. Core Paradigm: ECS & Observers

• •Components: Small, data-only structs. Use #[derive(Component)].
• •Reflect Auto-Registration (0.17): Types deriving Reflect no longer require manual registration in the app via .register_type::<T>() in most common cases.
• •Observers (The On Syntax): 0.17 formalizes the On<Event> syntax for observers.
  • •Pattern: commands.trigger(MyEvent);
  • •Listener: app.observe(|trigger: On<MyEvent>| { ... });
  • •Targeted: app.observe(|trigger: On<MyEvent, MyComponent>| { ... });
• •Entity Relationships: Use Entity IDs for links. In 0.17, commands.entity(parent).add_child(child) remains the standard for hierarchies.

2. States & Transitions

• •Same-State Transitions (0.17): You can now trigger transitions to the state the app is already in, which is useful for "restarting" levels or resetting state-scoped logic.
• •State-Scoped Entities: Tag entities with StateScoped(GameState::Playing). Enable with app.enable_state_scoped_entities::<GameState>();.
• •Computed States: Use for hierarchical state logic (e.g., InMenu is true if state is MainMenu OR Settings).

3. UI Development & Rendering

• •Feature Flags (Critical): In 0.17, the bevy_ui feature no longer implies rendering. If using default-features = false, you must include both bevy_ui and bevy_ui_render.
• •Headless Widgets (0.17): Experimental support for Button, Slider, and Checkbox that emit events (Activate, ValueChange) via the observer system.
• •Gradients & Borders: Bevy UI now supports background/border gradients and per-side border colors.
• •Layout: Uses Flexbox (Taffy). Prefer Node with Display::Flex. 0.17 introduces better support for rem units and sticky nodes.

4. Advanced Rendering (0.17)

• •Solari (Raytracing): Experimental real-time raytraced indirect lighting. Enable via AtmosphereMode::Raymarched for high-fidelity skies.
• •DLSS: Support for Deep Learning Super Sampling on Nvidia GPUs for upscaling and anti-aliasing.
• •Light Textures: Use textures to modulate light intensity (gobos/projected patterns).
• •Tilemap Chunk Rendering: New built-in performant way to render tilemaps in chunks.

5. System Scheduling

• •Run Conditions: Prefer .run_if(in_state(GameState::Playing)).
• •FixedUpdate: Use for physics/gameplay logic. 0.17 includes improved testing infrastructure for fixed timesteps.
• •Hotpatching (0.17): Initial integration for sub-second hot-reloading of Rust system code (limited to ECS systems).

6. Anti-Patterns

• •Don't manually cleanup state entities; use StateScoped.
• •Don't ignore UI rendering features; ensure bevy_ui_render is active if UI is invisible.
• •Don't use raw Trigger<E> if the simpler On<E> syntax suffices for your observer.