Bevy Genre Fighting Agent Skill

Bevy fighting

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

When to use

Load this for local fighting: frame flags, hitboxes as your data, and a round state. Rollback netcode is out of scope.

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. Frame data below is components and one round resource.

Examples

[dependencies]
bevy = "0.20"

Each fighter stores the frame index, advantage, and health. The round clock is a resource. Input, frame advance, and hit resolution share Fighter, so they chain on the fixed step.

#[derive(Component)]
struct Fighter {
    frame: u16,
    advantage: i16,
    health: i32,
}

#[derive(Component)]
struct Hitbox {
    active: bool,
    damage: i32,
    startup: u16,
    active_until: u16,
}

#[derive(Resource)]
struct RoundClock {
    frames_left: u32,
}

fn boot(mut commands: Commands) {
    commands.insert_resource(RoundClock { frames_left: 60 * 99 });
    commands.spawn((
        Fighter {
            frame: 0,
            advantage: 0,
            health: 10000,
        },
        Hitbox {
            active: false,
            damage: 400,
            startup: 4,
            active_until: 8,
        },
    ));
}

fn open_hitbox(mut fighters: Query<(&Fighter, &mut Hitbox)>) {
    for (fighter, mut hitbox) in &mut fighters {
        hitbox.active = fighter.frame >= hitbox.startup && fighter.frame < hitbox.active_until;
    }
}

fn advance_frames(mut fighters: Query<&mut Fighter>, mut round: ResMut<RoundClock>) {
    for mut fighter in &mut fighters {
        fighter.frame = fighter.frame.saturating_add(1);
    }
    round.frames_left = round.frames_left.saturating_sub(1);
}

fn apply_hits(hitboxes: Query<(Entity, &Hitbox)>, mut fighters: Query<(Entity, &mut Fighter)>) {
    let damage: i32 = hitboxes
        .iter()
        .filter(|(_, box_)| box_.active)
        .map(|(_, box_)| box_.damage)
        .sum();
    if damage == 0 {
        return;
    }
    for (entity, mut fighter) in &mut fighters {
        if hitboxes.iter().any(|(src, box_)| box_.active && src == entity) {
            continue;
        }
        fighter.health -= damage;
        fighter.advantage = -12;
    }
}

fn install(app: &mut App) {
    app.add_systems(Startup, boot).add_systems(
        FixedUpdate,
        (open_hitbox, advance_frames, apply_hits).chain(),
    );
}

A round ends when the clock or a health bar hits zero. That system only reads Fighter and RoundClock.

#[derive(Component)]
struct Fighter {
    frame: u16,
    advantage: i16,
    health: i32,
}

#[derive(Resource)]
struct RoundClock {
    frames_left: u32,
}

fn round_over(round: Res<RoundClock>, fighters: Query<&Fighter>) -> bool {
    round.frames_left == 0 || fighters.iter().any(|fighter| fighter.health <= 0)
}

Routing

• bevy-state-machines - Round and character mode.
• bevy-combat-system - Strike resolution.
• bevy-animation - Move clips.
• bevy-input-handling - Per-frame input.

Scope

• Local frame data is a Fighter component (frame index, advantage, health) plus a RoundClock resource. Bevy has no fighting-game type; the example above is the data.

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 | One mutable blob shared by every 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 | Read the official Bevy pages | 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 rollback or netcode crate. 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 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-state-machines - Round and character mode.
• bevy-combat-system - Strike resolution.
• bevy-animation - Move clips.
• bevy-input-handling - Per-frame input.

Downstream / consumers

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

Master

• bevy-master - Bevy router.