Bevy Open world (thin router)

Genre router. Domain work lives in the Bevy skills below.

When to use

Load this for streaming regions and distant actors. Do not invent a world-partition type.

ECS shape

• Components hold the genre's per-entity flags as plain data. This file does not name new engine types.
• Resources hold run-wide counters (score, wave index, seed) via bevy-data-resources.
• Systems read those components on Update or the fixed timestep from bevy-master. Order them with .chain() when a later system must see the result.
• Schedule: gameplay mode changes go through bevy-state-machines. Do not invent a genre plugin.

Routing

• bevy-asset-scenes - Region scenes.
• bevy-3d-world-building - Assembly.
• bevy-ai-navigation - Ambient actors.
• bevy-quest-system - Objectives.

Scope

Region membership and activation distance are components you own. Mesh LOD stays on bevy-3d-world-building.

Examples

[package]
name = "open-world"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.20"

A cell index on the player resource decides which residents are active. One system writes PlayerCell; the next inserts or removes Active.

#[derive(Component)]
struct Player;

#[derive(Component)]
struct Resident {
    cell: i32,
}

#[derive(Component)]
struct Active;

#[derive(Resource)]
struct PlayerCell(i32);

fn track_cell(players: Query<&Transform, With<Player>>, mut cell: ResMut<PlayerCell>) {
    for transform in &players {
        cell.0 = (transform.translation.x / 64.0).floor() as i32;
        break;
    }
}

fn activate(
    cell: Res<PlayerCell>,
    mut commands: Commands,
    idle: Query<(Entity, &Resident), Without<Active>>,
) {
    for (entity, resident) in &idle {
        if (resident.cell - cell.0).abs() <= 1 {
            commands.entity(entity).insert(Active);
        }
    }
}

fn deactivate(
    cell: Res<PlayerCell>,
    mut commands: Commands,
    active: Query<(Entity, &Resident), With<Active>>,
) {
    for (entity, resident) in &active {
        if (resident.cell - cell.0).abs() > 1 {
            commands.entity(entity).remove::<Active>();
        }
    }
}

pub struct RegionPlugin;

impl Plugin for RegionPlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(PlayerCell(0)).add_systems(
            Update,
            (track_cell, activate, deactivate).chain(),
        );
    }
}

Distant actors keep a home point and only move while Active is present.

#[derive(Component)]
struct Wander {
    home: Vec3,
    angle: f32,
}

fn wander(time: Res<Time>, mut actors: Query<(&mut Transform, &mut Wander), With<Active>>) {
    let dt = time.delta_secs();
    for (mut transform, mut wander) in &mut actors {
        wander.angle += dt;
        let offset = Vec3::new(wander.angle.sin() * 2.0, 0.0, wander.angle.cos() * 2.0);
        transform.translation = wander.home + offset;
    }
}

#[derive(Component)]
struct Active;

Spawn the player and a ring of residents from Startup.

#[derive(Component)]
struct Player;

#[derive(Component)]
struct Resident {
    cell: i32,
}

#[derive(Component)]
struct Wander {
    home: Vec3,
    angle: f32,
}

fn spawn_world(mut commands: Commands) {
    commands.spawn((Player, Transform::from_xyz(0.0, 0.0, 0.0)));
    for index in 0..5 {
        let home = Vec3::new(index as f32 * 64.0, 0.0, 0.0);
        commands.spawn((
            Resident { cell: index },
            Wander { home, angle: index as f32 },
            Transform::from_translation(home),
        ));
    }
}

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 scene-tree types in Bevy code. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No invented genre APIs. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• Do not pick a physics or net crate here. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

The library pin on bevy-master stays 0.20.0. Official links stay on the unversioned learn pages.

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 - ECS ownership and schedules.
• bevy-ecs-composition - Spawn and query shape.

Complements

• bevy-asset-scenes - Region scenes.
• bevy-3d-world-building - Assembly.
• bevy-ai-navigation - Ambient actors.
• bevy-quest-system - Objectives.

Downstream / consumers

• None. This router does not own a second implementation.

Master

• bevy-master - Bevy router.