Bevy 3D world building

When to use

Load this when placing meshes, lights, and colliders into a level. Scene spawn mechanics stay on bevy-asset-scenes. Physics bodies stay on bevy-physics-3d.

ECS shape

• Spawn: entities with transforms and render components. Primitives (Cuboid, Sphere, Cylinder) convert into Mesh and ride on Mesh3d plus MeshMaterial3d.
• Scenes: bevy_scene and bevy_gltf are features. Spawn details are on bevy-asset-scenes (AssetServer, scene spawn).
• Lights: a DirectionalLight is an entity with a Transform. Fog is DistanceFog on the camera entity. Full lighting setups stay on bevy-3d-lighting.
• Systems: which cells are present is a Resource. Spawning a cell is Commands in Update.

fn spawn_level(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let stone = materials.add(StandardMaterial {
        base_color: Color::srgb(0.45, 0.42, 0.38),
        ..default()
    });
    let floor = materials.add(StandardMaterial {
        base_color: Color::srgb(0.28, 0.30, 0.26),
        ..default()
    });
    commands.spawn((
        Mesh3d(meshes.add(Cuboid::new(24.0, 0.2, 24.0))),
        MeshMaterial3d(floor),
        Transform::from_xyz(0.0, -0.1, 0.0),
    ));
    commands.spawn((
        Mesh3d(meshes.add(Cylinder::new(0.4, 3.0))),
        MeshMaterial3d(stone.clone()),
        Transform::from_xyz(-4.0, 1.5, -2.0),
    ));
    commands.spawn((
        Mesh3d(meshes.add(Sphere::new(0.6))),
        MeshMaterial3d(stone),
        Transform::from_xyz(2.0, 0.6, 1.0),
    ));
    commands.spawn((
        DirectionalLight {
            illuminance: 12_000.0,
            shadow_maps_enabled: true,
            ..default()
        },
        Transform::from_xyz(6.0, 10.0, 4.0).looking_at(Vec3::ZERO, Vec3::Y),
    ));
    commands.spawn((
        Camera3d::default(),
        DistanceFog {
            color: Color::srgb(0.55, 0.62, 0.70),
            falloff: FogFalloff::Linear {
                start: 12.0,
                end: 40.0,
            },
            ..default()
        },
        Transform::from_xyz(0.0, 8.0, 14.0).looking_at(Vec3::ZERO, Vec3::Y),
    ));
}

Kitbash props are ordinary entities. A helper returns the entity id so later systems can parent markers to it.

fn spawn_prop(
    commands: &mut Commands,
    meshes: &mut Assets<Mesh>,
    materials: &mut Assets<StandardMaterial>,
    at: Vec3,
    size: Vec3,
    color: Color,
) -> Entity {
    commands
        .spawn((
            Mesh3d(meshes.add(Cuboid::from_size(size))),
            MeshMaterial3d(materials.add(StandardMaterial {
                base_color: color,
                ..default()
            })),
            Transform::from_translation(at),
        ))
        .id()
}

Cells already in the world live on one resource. The streamer inserts a marker component and a mesh only for cells that are not recorded yet.

#[derive(Resource, Default)]
struct LoadedCells {
    coords: Vec<(i32, i32)>,
}

#[derive(Component)]
struct CellMarker {
    x: i32,
    z: i32,
}

fn stream_cells(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    mut loaded: ResMut<LoadedCells>,
    focus: Query<&Transform, With<Camera3d>>,
) {
    let Ok(focus) = focus.single() else {
        return;
    };
    let cx = (focus.translation.x / 8.0).floor() as i32;
    let cz = (focus.translation.z / 8.0).floor() as i32;
    for dz in -1..=1 {
        for dx in -1..=1 {
            let coord = (cx + dx, cz + dz);
            if loaded.coords.contains(&coord) {
                continue;
            }
            loaded.coords.push(coord);
            commands.spawn((
                CellMarker {
                    x: coord.0,
                    z: coord.1,
                },
                Mesh3d(meshes.add(Cuboid::new(8.0, 0.1, 8.0))),
                MeshMaterial3d(materials.add(StandardMaterial {
                    base_color: Color::srgb(0.3, 0.34, 0.28),
                    ..default()
                })),
                Transform::from_xyz(coord.0 as f32 * 8.0, 0.0, coord.1 as f32 * 8.0),
            ));
        }
    }
}

[dependencies]
bevy = "0.20"

Level choices

Need	Bevy approach
Packed level	A scene asset spawned through bevy-asset-scenes
Kitbash props	Entities with Mesh3d and MeshMaterial3d
Atmosphere	DirectionalLight, DistanceFog, and the camera entity

Scope

• Primitives above cover greybox blocks, columns, and spheres. Heightmaps are a Mesh you fill yourself, then the same Mesh3d spawn.
• Collider authoring belongs with bevy-physics-3d once you choose a physics solver.

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 script field copied onto the entity
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 CSG, grid-map, or world-environment node types in Bevy code. WHY: greybox meshes, lights, and DistanceFog are the documented Bevy pieces.

• 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 links stay on bevy.org. The library pin on bevy-master stays 0.20.0.

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-asset-scenes - Scene spawn.
• bevy-3d-lighting - Lights.
• bevy-3d-materials - Surfaces.
• bevy-camera-systems - View.

Complements

• bevy-procedural-generation - Generated layouts.
• bevy-physics-3d - Simulated props. Solver still unpicked.
• godot-3d-world-building - Same topic on the Godot track.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.