Bevy Engine

Entities, components, systems, and schedules - the Bevy ECS game engine in Rust.

Recipe

use bevy::prelude::*;
 
#[derive(Component)]
struct Velocity(Vec2);
 
fn move_system(mut query: Query<(&mut Transform, &Velocity)>, time: Res<Time>) {
    for (mut transform, velocity) in &mut query {
        transform.translation += velocity.0.extend(0.0) * time.delta_secs();
    }
}

When to reach for this:

• 2D/3D games wanting data-oriented Rust engine
• Prototyping with hot reload and strong ECS patterns
• Tools simulating many agents with parallel systems
• Learning ECS without building engine infrastructure

Working Example

use bevy::prelude::*;
 
#[derive(Component)]
struct Player;
 
#[derive(Component)]
struct Velocity(Vec2);
 
fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, (player_input, move_system))
        .run();
}
 
fn setup(mut commands: Commands) {
    commands.spawn((Player, Velocity(Vec2::ZERO), Transform::default()));
    commands.spawn(Camera2d);
}
 
fn player_input(
    keys: Res<ButtonInput<KeyCode>>,
    mut q: Query<&mut Velocity, With<Player>>,
) {
    let mut v = Vec2::ZERO;
    if keys.pressed(KeyCode::KeyW) { v.y += 1.0; }
    if keys.pressed(KeyCode::KeyS) { v.y -= 1.0; }
    if keys.pressed(KeyCode::KeyA) { v.x -= 1.0; }
    if keys.pressed(KeyCode::KeyD) { v.x += 1.0; }
    for mut vel in &mut q {
        vel.0 = v.normalize_or_zero() * 300.0;
    }
}
 
fn move_system(mut query: Query<(&mut Transform, &Velocity)>, time: Res<Time>) {
    for (mut t, v) in &mut query {
        t.translation += v.0.extend(0.0) * time.delta_secs();
    }
}

What this demonstrates:

• Input system writes Velocity; movement system reads it
• With<Player> filter targets player entity
• Delta-time scaled translation in Update

Deep Dive

How It Works

• World stores entities, components, resources.
• Schedule orders systems; executor runs non-conflicting queries in parallel.
• Commands deferred structural changes (spawn/despawn/insert).
• Plugins register systems, assets, and render nodes modularly.

ECS Building Blocks

Gotchas

• Query conflicts - two systems mutably accessing same component without ordering fail scheduler. Fix: chain with .before/.after or merge systems.
• Spawn after despawn same frame - entity ID reuse confusion. Fix: use commands buffer semantics; avoid holding Entity across frames without validation.
• Huge monolithic systems - kills parallelism. Fix: split by component subsets.
• Assuming asset loaded instantly - pink placeholders. Fix: check LoadState or use SceneBundle when ready.
• Bevy version drift - tutorial API mismatches. Fix: match book to exact crate version.

Alternatives

FAQs

Related

• Game Dev Basics - orientation
• Assets & Scenes - loading
• Game Loops & Timing - schedules
• Performance for Games - optimization

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.