Bevy adapt 2D to 3D

When to use

Load this when a 2D design should gain a 3D camera and meshes. Keep gameplay components. Swap the camera and the drawable.

ECS shape

• Cameras: Camera2d and Camera3d are already documented on bevy-camera-systems. An entity should not keep both as if they were one camera mode unless that skill says so.
• Draw: Sprite is 2D. Meshes and StandardMaterial are 3D (bevy-3d-materials).
• Features: the crate page separates 2d and 3d profiles. Enabling 3D does not delete 2D types.
• Motion: bevy-character-movement stays the locomotion skill. A 3D velocity is still your component until a solver exists.

What changes

Keep	Replace
Gameplay components on the actor	Sprite with Mesh3d and MeshMaterial3d
The camera entity	Camera2d with Camera3d and a perspective Projection
Planar motion as data	Vec2 velocity with a Vec3 wish on XZ

There is no conversion helper. A startup system rewrites the entities you already spawned. Physics solvers stay on the physics skills.

[dependencies]
bevy = "0.20"

use bevy::mesh::Meshable;

#[derive(Component)]
struct Actor;

#[derive(Component)]
struct PlanarVelocity(Vec2);

#[derive(Component)]
struct WishVelocity(Vec3);

fn promote_actors(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    actors: Query<(Entity, &Transform), (With<Actor>, With<Sprite>)>,
) {
    let mesh = meshes.add(Cuboid::new(0.8, 1.6, 0.8).mesh());
    let material = materials.add(StandardMaterial {
        base_color: Color::srgb(0.75, 0.45, 0.25),
        ..default()
    });
    for (entity, transform) in &actors {
        let ground = Vec3::new(transform.translation.x, 0.8, transform.translation.y);
        commands.entity(entity).remove::<Sprite>().insert((
            Mesh3d(mesh.clone()),
            MeshMaterial3d(material.clone()),
            Transform::from_translation(ground),
        ));
    }
}

fn promote_camera(mut commands: Commands, cameras: Query<Entity, With<Camera2d>>) {
    for entity in &cameras {
        commands.entity(entity).remove::<Camera2d>().insert((
            Camera3d::default(),
            Projection::Perspective(PerspectiveProjection::default()),
            Transform::from_xyz(0.0, 6.0, 12.0).looking_at(Vec3::ZERO, Vec3::Y),
        ));
    }
}
fn lift_velocity(mut actors: Query<(&PlanarVelocity, &mut WishVelocity), With<Actor>>) {
    for (planar, mut wish) in &mut actors {
        wish.0 = Vec3::new(planar.0.x, 0.0, planar.0.y);
    }
}

pub struct AdaptTo3dPlugin;

impl Plugin for AdaptTo3dPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, (promote_actors, promote_camera).chain())
            .add_systems(FixedUpdate, lift_velocity);
    }
}

fn spawn_follow_camera(mut commands: Commands) {
    commands.spawn((
        Camera3d::default(),
        Projection::Perspective(PerspectiveProjection {
            fov: 50.0_f32.to_radians(),
            ..default()
        }),
        Transform::from_xyz(0.0, 4.0, 8.0).looking_at(Vec3::new(0.0, 1.0, 0.0), Vec3::Y),
    ));
}

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	One script that owns the whole actor
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 node convert-to-3D operation from another engine. WHY: Bevy has no scene-tree convert; a startup system removes Sprite and inserts mesh components on the same entity.

• No foreign engine types in Bevy code. WHY: Camera3d and Mesh3d are the draw path this schedule already runs.

• 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. Load references/ecs-ownership.md when a system both removes 2D components and writes a velocity. Do not load it to author materials.

Official Documentation

• 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.
• bevy-camera-systems - Camera2d and Camera3d.
• bevy-3d-world-building - Level assembly.

Complements

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

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.