bevy-particles

Bevy particles

When to use

Load this before adding a burst, trail, or GPU particle effect. Particle effects are yours to build in ECS. Do not invent a particle plugin.

ECS shape

• Components own each mote (Particle) and each emitter (Emitter). A Sprite is the visible quad.
• Resources: none. Burst origin and rate live on the emitter entity.
• Systems: one system spawns motes, one integrates them and despawns the dead.
• Schedule: both run on FixedUpdate, chained so a mote spawned this step is integrated next step.

Coming from Godot

Godot idea	Bevy idiom
CPU particles	Entities with Particle, Sprite, and Transform
GPU particles	The same entities, drawn by the sprite pipeline
One-shot burst	Spawn a fixed count, then despawn when life hits zero

Scope

Bevy ships no particle module. A burst is a spawn loop over Sprite entities. A trail is an emitter component that spends a rate accumulator.

Examples

[package]
name = "particles"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.20"
rand = "0.9"

A one-shot burst scatters sprites. Each mote stores velocity and remaining life.

use rand::Rng;

#[derive(Component)]
struct Particle {
    velocity: Vec2,
    life: f32,
}

fn burst(mut commands: Commands) {
    let mut rng = rand::rng();
    for _ in 0..24 {
        let angle = rng.random_range(0.0..std::f32::consts::TAU);
        let speed = rng.random_range(1.0..4.0);
        commands.spawn((
            Particle {
                velocity: Vec2::new(angle.cos(), angle.sin()) * speed,
                life: rng.random_range(0.3..0.8),
            },
            Sprite {
                color: Color::srgba(1.0, 0.45, 0.1, 1.0),
                custom_size: Some(Vec2::splat(6.0)),
                ..default()
            },
            Transform::from_xyz(0.0, 0.0, 0.0),
        ));
    }
}

Integration writes Transform and despawns when life expires. Gravity is a constant acceleration on Y.

#[derive(Component)]
struct Particle {
    velocity: Vec2,
    life: f32,
}

fn simulate(
    time: Res<Time<Fixed>>,
    mut commands: Commands,
    mut motes: Query<(Entity, &mut Transform, &mut Particle, &mut Sprite)>,
) {
    let dt = time.delta_secs();
    for (entity, mut transform, mut particle, mut sprite) in &mut motes {
        particle.life -= dt;
        if particle.life <= 0.0 {
            commands.entity(entity).despawn();
            continue;
        }
        particle.velocity.y -= 6.0 * dt;
        transform.translation.x += particle.velocity.x * dt;
        transform.translation.y += particle.velocity.y * dt;
        sprite.color.set_alpha(particle.life.clamp(0.0, 1.0));
    }
}

An emitter on a moving entity spends accumulator and spawns motes at its translation. That is a trail.

use rand::Rng;

#[derive(Component)]
struct Emitter {
    rate: f32,
    accumulator: f32,
}

#[derive(Component)]
struct Particle {
    velocity: Vec2,
    life: f32,
}

fn emit(
    time: Res<Time<Fixed>>,
    mut commands: Commands,
    mut emitters: Query<(&Transform, &mut Emitter)>,
) {
    let dt = time.delta_secs();
    let mut rng = rand::rng();
    for (transform, mut emitter) in &mut emitters {
        emitter.accumulator += emitter.rate * dt;
        while emitter.accumulator >= 1.0 {
            emitter.accumulator -= 1.0;
            commands.spawn((
                Particle {
                    velocity: Vec2::new(rng.random_range(-0.4..0.4), rng.random_range(0.2..1.0)),
                    life: 0.6,
                },
                Sprite {
                    color: Color::srgba(0.7, 0.7, 0.7, 0.8),
                    custom_size: Some(Vec2::splat(4.0)),
                    ..default()
                },
                Transform::from_translation(transform.translation),
            ));
        }
    }
}

fn simulate(
    time: Res<Time<Fixed>>,
    mut commands: Commands,
    mut motes: Query<(Entity, &mut Transform, &mut Particle, &mut Sprite)>,
) {
    let dt = time.delta_secs();
    for (entity, mut transform, mut particle, mut sprite) in &mut motes {
        particle.life -= dt;
        if particle.life <= 0.0 {
            commands.entity(entity).despawn();
            continue;
        }
        particle.velocity.y -= 6.0 * dt;
        transform.translation.x += particle.velocity.x * dt;
        transform.translation.y += particle.velocity.y * dt;
        sprite.color.set_alpha(particle.life.clamp(0.0, 1.0));
    }
}

pub struct ParticlePlugin;

impl Plugin for ParticlePlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(FixedUpdate, (emit, simulate).chain());
    }
}

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	Component	One system via Query	Update or FixedMain
One value for the whole app	Resource	One system	Startup to insert, then the schedule that reads it
Spawn	Commands	The spawning system	Startup for the initial world; later schedules for runtime spawn
Order that must not race	.chain()	The chained systems only	Same schedule
Plugin boundary	Plugin	build registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	Component + Query	A Godot node script
App-wide config or clock	Resource	Copy the value onto every entity
Stable simulation step	FixedMain and the Fixed clock	Tie simulation to raw frame Update
Startup spawn	Commands in Startup	Spawn from a render system
Cross-system notice that is not shared state	Message or observer slot in bevy-events-messaging	A new event type invented in this file
An API outside the documented set	Check the official docs first	A made-up crate or API

Load references/ecs-ownership.md for the ownership table.

NEVER

• Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.

• Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• No Godot particle node types. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No named particle crate as the chosen solution. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No Godot types in Bevy code. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No invented APIs or unnamed third-party crates as the chosen solver. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

Official Documentation

• bevy crate - API reference and Cargo feature list.
• Assets - Official asset catalog. No third-party crate was selected.
• Examples - Example tree on the latest branch.
• ECS - Component, systems, Query, Startup, Update, and .chain().
• Plugins - Plugin, DefaultPlugins, MinimalPlugins, and add_plugins.

Related Skills

Prerequisites

• bevy-master - Hub and schedules.
• bevy-ecs-composition - Components and systems.

Complements

• bevy-shaders - Materials are not a particle system.
• godot-particles - Equivalent Godot skill.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.