Bevy RTS (thin router)

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

When to use

Load this for selection, orders, and groups.

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-input-handling - Selection clicks.
• bevy-ai-navigation - Move orders and navigation.
• bevy-combat-system - Attacks.
• bevy-economy-system - Costs.

Scope

Selection, move orders, and control groups are components and one resource. Pathfinding stays on bevy-ai-navigation.

Examples

[package]
name = "rts"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.20"

Selected marks the current group. A move order is a target point. March runs after the order is written.

#[derive(Component)]
struct Selected;

#[derive(Component)]
struct MoveOrder {
    target: Vec3,
}

fn issue_move(keys: Res<ButtonInput<KeyCode>>, mut units: Query<&mut MoveOrder, With<Selected>>) {
    if !keys.just_pressed(KeyCode::KeyM) {
        return;
    }
    for mut order in &mut units {
        order.target = Vec3::new(12.0, 0.0, 6.0);
    }
}

fn march(time: Res<Time<Fixed>>, mut units: Query<(&MoveOrder, &mut Transform)>) {
    let dt = time.delta_secs();
    for (order, mut transform) in &mut units {
        let delta = order.target - transform.translation;
        let step = 6.0 * dt;
        if delta.length() <= step {
            transform.translation = order.target;
        } else {
            transform.translation += delta.normalize_or_zero() * step;
        }
    }
}

pub struct OrderPlugin;

impl Plugin for OrderPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(FixedUpdate, (issue_move, march).chain());
    }
}

Number keys store the selected entities on a resource. Pressing the key again clears Selected and restores the group.

#[derive(Resource, Default)]
struct ControlGroup {
    members: Vec<Entity>,
}

#[derive(Component)]
struct Selected;

fn bind_group(
    keys: Res<ButtonInput<KeyCode>>,
    selected: Query<Entity, With<Selected>>,
    mut group: ResMut<ControlGroup>,
    mut commands: Commands,
) {
    if keys.just_pressed(KeyCode::Digit1) && keys.pressed(KeyCode::ControlLeft) {
        group.members.clear();
        for entity in &selected {
            group.members.push(entity);
        }
        return;
    }
    if keys.just_pressed(KeyCode::Digit1) {
        for entity in &selected {
            commands.entity(entity).remove::<Selected>();
        }
        for entity in group.members.clone() {
            commands.entity(entity).insert(Selected);
        }
    }
}

Click-select uses a pointer resource filled by another system. Units inside the radius gain Selected.

#[derive(Resource)]
struct PointerWorld(Vec3);

#[derive(Component)]
struct Selectable;

#[derive(Component)]
struct Selected;

fn click_select(
    buttons: Res<ButtonInput<MouseButton>>,
    pointer: Res<PointerWorld>,
    mut commands: Commands,
    units: Query<(Entity, &Transform), With<Selectable>>,
    selected: Query<Entity, With<Selected>>,
) {
    if !buttons.just_pressed(MouseButton::Left) {
        return;
    }
    for entity in &selected {
        commands.entity(entity).remove::<Selected>();
    }
    for (entity, transform) in &units {
        if transform.translation.distance(pointer.0) < 1.5 {
            commands.entity(entity).insert(Selected);
        }
    }
}

fn spawn_units(mut commands: Commands) {
    commands.insert_resource(PointerWorld(Vec3::ZERO));
    for index in 0..4 {
        commands.spawn((
            Selectable,
            MoveOrder {
                target: Vec3::new(index as f32 * 2.0, 0.0, 0.0),
            },
            Transform::from_xyz(index as f32 * 2.0, 0.0, 0.0),
        ));
    }
}

#[derive(Component)]
struct MoveOrder {
    target: Vec3,
}

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-input-handling - Selection clicks.
• bevy-ai-navigation - Move orders and navigation.
• bevy-combat-system - Attacks.
• bevy-economy-system - Costs.

Downstream / consumers

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

Master

• bevy-master - Bevy router.