Bevy adapt 3D to 2D

When to use

Load this when a 3D design should render as sprites or billboards. Gameplay components stay. Render components change.

ECS shape

• Draw: replace mesh and PBR material entities' render parts with Sprite where a billboard is enough.
• Camera: use Camera2d from bevy-camera-systems.
• Lights: 3D light entities are not required for an unlit sprite. Do not leave clustered-light assumptions in gameplay code.

What stays and what changes

Piece	Bevy idiom
Gameplay on the actor	Keep the same components. Swap render components for Sprite.
View	Camera2d.
Draw order	A DrawOrder component you store, then write into Transform.

Examples

[dependencies]
bevy = "0.20"

Gameplay components stay on the entity. The 3D render components come off, and a Sprite goes on. Camera2d is the view.

#[derive(Component)]
struct Actor;

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

fn spawn_flat_view(mut commands: Commands) {
    commands.spawn(Camera2d);
}

fn present_as_sprites(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    actors: Query<(Entity, &DrawOrder), With<Actor>>,
) {
    let image = asset_server.load("actors/hero.png");
    for (entity, order) in &actors {
        commands
            .entity(entity)
            .remove::<Mesh3d>()
            .remove::<MeshMaterial3d<StandardMaterial>>()
            .insert((
                Sprite {
                    image: image.clone(),
                    custom_size: Some(Vec2::new(64.0, 64.0)),
                    ..default()
                },
                Transform::from_xyz(0.0, order.0, 0.0),
            ));
    }
}

A new actor can spawn already flat. The same Actor component is what gameplay systems query.

#[derive(Component)]
struct Actor;

fn spawn_sprite_actor(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn((
        Actor,
        Sprite {
            image: asset_server.load("actors/hero.png"),
            color: Color::WHITE,
            ..default()
        },
        Transform::from_xyz(0.0, 0.0, 0.0),
    ));
}

fn face_motion(mut actors: Query<(&Transform, &mut Sprite), With<Actor>>) {
    for (transform, mut sprite) in &mut actors {
        sprite.flip_x = transform.translation.x < 0.0;
    }
}

Sort sprites from the stored order without a 3D camera. Higher DrawOrder maps to a higher Y so the 2D camera draws it later in a top-down layout.

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

fn apply_draw_order(mut sprites: Query<(&DrawOrder, &mut Transform), With<Sprite>>) {
    for (order, mut transform) in &mut sprites {
        transform.translation.y = order.0;
    }
}

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 plain struct stored outside the world
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 leftover Mesh3d or MeshMaterial3d on an entity that is now a sprite. WHY: both render paths on one entity fight over the same transform.

• 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

The library pin on bevy-master stays 0.20.0. Permalinks stay unversioned.

Official Documentation

• Assets - Official asset catalog. No third-party crate was selected.
• Examples - Example tree on the latest branch.
• 2D examples - Sprite and camera samples.
• 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.
• bevy-camera-systems - Camera2d.
• bevy-2d-animation - Sprite clips.

Complements

• bevy-adapt-2d-to-3d - The reverse adapt.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.