Bevy Rhythm (thin router)

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

When to use

Load this for chart time and hit windows aligned to audio.

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. This file registers only the chart clock and the hit judge.

Routing

• bevy-audio-systems - Music playback.
• bevy-input-handling - Hits.
• bevy-game-loop-time-trial - Score time.

Scope

Chart notes, the song clock, and hit windows live here. Playback, input devices, and score presentation stay in the skills linked above.

[dependencies]
bevy = "0.20"

#[derive(Component)]
struct ChartNote {
    hit_at: f32,
    lane: u8,
    judged: bool,
}

#[derive(Resource)]
struct HitWindow {
    perfect: f32,
    good: f32,
}

#[derive(Resource, Default)]
struct ChartClock(f32);

fn advance_chart(time: Res<Time>, mut clock: ResMut<ChartClock>) {
    clock.0 += time.delta_secs();
}

pub struct ClockPlugin;

impl Plugin for ClockPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<ChartClock>()
            .add_systems(Update, advance_chart);
    }
}

#[derive(Component)]
struct ChartNote {
    hit_at: f32,
    lane: u8,
    judged: bool,
    grade: u8,
}

#[derive(Resource)]
struct HitWindow {
    perfect: f32,
    good: f32,
}

#[derive(Resource, Default)]
struct ChartClock(f32);

fn judge(
    keys: Res<ButtonInput<KeyCode>>,
    clock: Res<ChartClock>,
    window: Res<HitWindow>,
    mut notes: Query<&mut ChartNote>,
) {
    if !keys.just_pressed(KeyCode::KeyF) {
        return;
    }
    for mut note in &mut notes {
        if note.judged || note.lane != 0 {
            continue;
        }
        let delta = (clock.0 - note.hit_at).abs();
        if delta <= window.perfect {
            note.judged = true;
            note.grade = 2;
        } else if delta <= window.good {
            note.judged = true;
            note.grade = 1;
        }
    }
}

pub struct JudgePlugin;

impl Plugin for JudgePlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(HitWindow {
            perfect: 0.04,
            good: 0.09,
        })
        .add_systems(Update, judge);
    }
}

#[derive(Component)]
struct ChartNote {
    hit_at: f32,
    lane: u8,
    judged: bool,
    grade: u8,
}

fn spawn_chart(mut commands: Commands) {
    for (index, lane) in [0u8, 1, 0, 2].into_iter().enumerate() {
        commands.spawn(ChartNote {
            hit_at: 1.0 + index as f32 * 0.5,
            lane,
            judged: false,
            grade: 0,
        });
    }
}

pub struct ChartPlugin;

impl Plugin for ChartPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, spawn_chart);
    }
}

fn main() {
    App::new()
        .add_plugins(MinimalPlugins)
        .add_plugins(ChartPlugin)
        .run();
}

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.

• Do not treat every press inside the wide window as perfect. WHY: the tight window writes grade 2 and the wide window writes grade 1.

• 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 pages stay on the unversioned site.

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-audio-systems - Music playback.
• bevy-input-handling - Hits.
• bevy-game-loop-time-trial - Score time.

Downstream / consumers

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

Master

• bevy-master - Bevy router.