Bevy Racing (thin router)

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

When to use

Load this for laps, splits, and vehicle motion you own.

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-game-loop-time-trial - Splits.
• bevy-character-movement - Stand-in motion until a vehicle solver exists.
• bevy-3d-world-building - Track.

Scope

Lap index, gate order, and a kinematic vehicle are components. A rigid-body vehicle solver stays on the physics skill once one is chosen.

Examples

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

[dependencies]
bevy = "0.20"

Gates are entities. The racer stores the next gate index and the lap count. Crossing the last gate increments the lap and records the clock.

#[derive(Component)]
struct Racer {
    lap: u32,
    next_gate: u32,
    gate_count: u32,
}

#[derive(Component)]
struct Gate {
    index: u32,
}

#[derive(Resource)]
struct RaceClock {
    elapsed: f32,
    best_lap: f32,
    lap_start: f32,
}

fn tick_clock(time: Res<Time<Fixed>>, mut clock: ResMut<RaceClock>) {
    clock.elapsed += time.delta_secs();
}

fn cross_gates(
    mut racers: Query<(&Transform, &mut Racer)>,
    gates: Query<(&Transform, &Gate)>,
    mut clock: ResMut<RaceClock>,
) {
    for (transform, mut racer) in &mut racers {
        for (gate_tf, gate) in &gates {
            if gate.index != racer.next_gate {
                continue;
            }
            if transform.translation.distance(gate_tf.translation) > 6.0 {
                continue;
            }
            let last = racer.gate_count.saturating_sub(1);
            if gate.index == last {
                let lap_time = clock.elapsed - clock.lap_start;
                if racer.lap == 0 || lap_time < clock.best_lap {
                    clock.best_lap = lap_time;
                }
                clock.lap_start = clock.elapsed;
                racer.lap += 1;
                racer.next_gate = 0;
            } else {
                racer.next_gate += 1;
            }
        }
    }
}

pub struct RacePlugin;

impl Plugin for RacePlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(RaceClock {
            elapsed: 0.0,
            best_lap: f32::MAX,
            lap_start: 0.0,
        })
        .add_systems(FixedUpdate, (tick_clock, cross_gates).chain());
    }
}

Heading and speed live on the vehicle. Input changes them; one system writes Transform.

#[derive(Component)]
struct Vehicle {
    speed: f32,
    heading: f32,
}

fn drive(
    time: Res<Time<Fixed>>,
    keys: Res<ButtonInput<KeyCode>>,
    mut vehicles: Query<(&mut Transform, &mut Vehicle)>,
) {
    let dt = time.delta_secs();
    for (mut transform, mut vehicle) in &mut vehicles {
        if keys.pressed(KeyCode::KeyA) {
            vehicle.heading += dt * 1.5;
        }
        if keys.pressed(KeyCode::KeyD) {
            vehicle.heading -= dt * 1.5;
        }
        if keys.pressed(KeyCode::KeyW) {
            vehicle.speed = (vehicle.speed + dt * 12.0).min(40.0);
        } else {
            vehicle.speed = (vehicle.speed - dt * 8.0).max(0.0);
        }
        let forward = Vec3::new(vehicle.heading.sin(), 0.0, vehicle.heading.cos());
        transform.translation += forward * vehicle.speed * dt;
    }
}

Startup places the car and three gates along Z.

#[derive(Component)]
struct Racer {
    lap: u32,
    next_gate: u32,
    gate_count: u32,
}

#[derive(Component)]
struct Gate {
    index: u32,
}

#[derive(Component)]
struct Vehicle {
    speed: f32,
    heading: f32,
}

fn spawn_track(mut commands: Commands) {
    commands.spawn((
        Racer {
            lap: 0,
            next_gate: 0,
            gate_count: 3,
        },
        Vehicle {
            speed: 0.0,
            heading: 0.0,
        },
        Transform::from_xyz(0.0, 0.0, 0.0),
    ));
    for index in 0..3 {
        commands.spawn((
            Gate { index },
            Transform::from_xyz(0.0, 0.0, 20.0 + index as f32 * 30.0),
        ));
    }
}

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-game-loop-time-trial - Splits.
• bevy-character-movement - Stand-in motion until a vehicle solver exists.
• bevy-3d-world-building - Track.

Downstream / consumers

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

Master

• bevy-master - Bevy router.