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

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

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

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.