nubiv/bevy-pro

Bevy Pro

Quick start

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, movement)
        .run();
}

#[derive(Component)]
struct Player;

#[derive(Component)]
struct Speed(f32);

fn setup(mut commands: Commands) {
    commands.spawn(Camera2d);
    commands.spawn((Player, Speed(200.0), Transform::default()));
}

fn movement(
    keyboard: Res<ButtonInput<KeyCode>>,
    mut query: Query<(&mut Transform, &Speed), With<Player>>,
    time: Res<Time>,
) {
    for (mut tf, speed) in &mut query {
        let mut dir = Vec2::ZERO;
        if keyboard.pressed(KeyCode::KeyW) { dir.y += 1.0; }
        if keyboard.pressed(KeyCode::KeyS) { dir.y -= 1.0; }
        if keyboard.pressed(KeyCode::KeyA) { dir.x -= 1.0; }
        if keyboard.pressed(KeyCode::KeyD) { dir.x += 1.0; }
        tf.translation += dir.normalize_or_zero().extend(0.0) * speed.0 * time.delta_secs();
    }
}

Core patterns

See REFERENCE.md for full ECS, rendering, input, UI, state, asset, and architecture patterns.

Workflows

New game project

1. cargo init && cargo add bevy (current: 0.19.0-dev)
2. Create main.rs with App::new().add_plugins(DefaultPlugins)
3. Add startup system for camera + initial entities
4. Add update systems for game logic
5. Organize into plugins as complexity grows

Adding a feature

1. Define components (#[derive(Component)])
2. Define resources if needed (#[derive(Resource)])
3. Write systems as plain functions with typed params
4. Register in a Plugin's build() method
5. Use .chain() or SystemSets for ordering

State management

1. Define states enum (#[derive(States)])
2. .init_state::<MyState>() in app
3. OnEnter/OnExit for setup/cleanup
4. .run_if(in_state(State::X)) for conditional systems
5. NextState<T> resource to transition

Key rules

• Composition over inheritance - many small components, not large monoliths
• Marker components - empty structs for query filtering with With<T>/Without<T>
• Commands for deferred ops - spawn/despawn/insert via Commands, not direct world mutation
• Change detection - use Changed<T>, Added<T> filters; call set_if_neq() to avoid false positives
• Plugin encapsulation - group related systems/resources/events into plugins
• Parallel by default - only use .chain() or .before()/.after() when ordering matters
• Handle-based assets - store Handle<T>, never clone loaded asset data
• DespawnOnExit(State) - auto-cleanup entities tied to states
• Newtype wrappers - wrap Timer, Handle, primitives for type safety
• Startup vs Update - one-time setup in Startup, per-frame logic in Update