Bevy Genre Card Game Agent Skill

Bevy card game

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

When to use

Load this for a local card zone, hand, and turn order.

ECS shape

• Components hold the genre's per-entity flags as plain data. This file does not name new engine types.
• Resources hold the turn index, energy, and the card catalog 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.

Idioms

| Need | Bevy shape |

| --- | --- |

| Cards and zones | Entities with Card and InZone |

| Turn and catalog | Resources |

| End turn, draw, play | Messages consumed on one .chain() |

Routing

• bevy-turn-system - Turns.
• bevy-inventory-system - Zones as containers of card ids.
• bevy-ui-layout - Hand layout.
• bevy-data-resources - Card definitions.

Scope

• A card is an entity. Its zone is a component. Turn index and the definition table are resources.
• Local play shuffles with rand. Online play stays on the networking skills.

Examples

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

[dependencies]
bevy = "0.20"
rand = "0.9"

Zones and the active seat are plain data. Ending a turn advances the seat, then draws one card into that seat's hand.

#[derive(Clone, Copy, PartialEq, Eq)]
enum ZoneKind {
    Deck,
    Hand,
    Board,
}

#[derive(Component)]
struct Card {
    def: u32,
}

#[derive(Component)]
struct InZone {
    owner: u8,
    kind: ZoneKind,
    order: u16,
}

#[derive(Resource)]
struct Turn {
    active: u8,
    players: u8,
}

#[derive(Message)]
struct EndTurn;

fn end_turn(mut turns: MessageReader<EndTurn>, mut turn: ResMut<Turn>) {
    for _end in turns.read() {
        turn.active = (turn.active + 1) % turn.players.max(1);
    }
}

fn draw_one(turn: Res<Turn>, mut ends: MessageReader<EndTurn>, mut cards: Query<(Entity, &mut InZone)>) {
    if ends.read().next().is_none() {
        return;
    }
    let mut next_order = 0u16;
    let mut pick: Option<Entity> = None;
    for (entity, zone) in &cards {
        if zone.owner != turn.active {
            continue;
        }
        if zone.kind == ZoneKind::Hand {
            next_order = next_order.max(zone.order.saturating_add(1));
        }
        if zone.kind == ZoneKind::Deck && pick.is_none() {
            pick = Some(entity);
        }
    }
    if let Some(entity) = pick {
        if let Ok((_entity, mut zone)) = cards.get_mut(entity) {
            zone.kind = ZoneKind::Hand;
            zone.order = next_order;
        }
    }
}

pub struct CardLoopPlugin;

impl Plugin for CardLoopPlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(Turn {
            active: 0,
            players: 2,
        })
        .add_message::<EndTurn>()
        .add_systems(Update, (end_turn, draw_one).chain());
    }
}

Shuffle writes a new deck order from rand::rng. Run it from Startup before the first draw.

use rand::seq::SliceRandom;

#[derive(Component)]
struct InZone {
    owner: u8,
    order: u16,
}

fn shuffle_deck(mut cards: Query<&mut InZone>) {
    let mut order: Vec<u16> = (0..cards.iter().count() as u16).collect();
    order.shuffle(&mut rand::rng());
    for (mut zone, index) in cards.iter_mut().zip(order) {
        zone.order = index;
    }
}

Definitions sit in one resource. The entity only stores the id.

#[derive(Clone, Copy, PartialEq, Eq)]
enum ZoneKind {
    Hand,
    Board,
}

#[derive(Component)]
struct InZone {
    kind: ZoneKind,
}

#[derive(Clone, Copy)]
struct CardDef {
    id: u32,
    cost: u8,
}

#[derive(Resource)]
struct CardCatalog {
    rows: Vec<CardDef>,
}

#[derive(Component)]
struct Card {
    def: u32,
}

fn cost_of(catalog: &CardCatalog, card: &Card) -> u8 {
    catalog
        .rows
        .iter()
        .find(|row| row.id == card.def)
        .map(|row| row.cost)
        .unwrap_or(0)
}

#[derive(Message)]
struct PlayCard {
    card: Entity,
}

fn play_card(
    mut plays: MessageReader<PlayCard>,
    catalog: Res<CardCatalog>,
    mut cards: Query<(&Card, &mut InZone)>,
    mut energy: ResMut<Energy>,
) {
    for play in plays.read() {
        let Ok((card, mut zone)) = cards.get_mut(play.card) else {
            continue;
        };
        if zone.kind != ZoneKind::Hand {
            continue;
        }
        let cost = cost_of(&catalog, card);
        if energy.left < cost {
            continue;
        }
        energy.left -= cost;
        zone.kind = ZoneKind::Board;
    }
}

#[derive(Resource)]
struct Energy {
    left: u8,
}

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 | A scene-tree script on the actor |

| 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 manual linked below | 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 scene-tree node or signal bus in this router. 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.

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-turn-system - Turns.
• bevy-inventory-system - Zones as containers of card ids.
• bevy-ui-layout - Hand layout.
• bevy-data-resources - Card definitions.

Downstream / consumers

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

Master

• bevy-master - Bevy router.