Bevy Roguelike (thin router)

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

When to use

Load this for run seeds, room generation, and permadeath flags.

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-procedural-generation - Seed and spawn.
• bevy-turn-system - Turn order when the run is turn-based.
• bevy-inventory-system - Run loot.
• bevy-rpg-stats - Run stats.

Examples

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

The run seed is one resource. Rooms are entities. StdRng is built inside the system so the seed stays on the resource.

use rand::rngs::StdRng;
use rand::{Rng, SeedableRng};

#[derive(Resource)]
struct RunSeed(u64);

#[derive(Component)]
struct Room {
    x: i32,
    y: i32,
}

fn carve(mut commands: Commands, seed: Res<RunSeed>) {
    let mut rng = StdRng::seed_from_u64(seed.0);
    for _ in 0..8 {
        commands.spawn(Room {
            x: rng.random_range(-6..6),
            y: rng.random_range(-6..6),
        });
    }
}

fn install_run(app: &mut App) {
    app.insert_resource(RunSeed(0x5EED))
        .add_systems(Startup, carve);
}

Permadeath is a flag on the actor plus a run-wide resource. One system writes both.

#[derive(Component)]
struct Actor {
    hp: i32,
}

#[derive(Resource)]
struct RunOver(bool);

fn permadeath(mut actors: Query<&mut Actor>, mut over: ResMut<RunOver>) {
    for mut actor in &mut actors {
        if actor.hp > 0 {
            continue;
        }
        actor.hp = 0;
        over.0 = true;
    }
}

Turn energy accumulates on a resource. Acting spends it. Chain the two systems because both write TurnClock.

#[derive(Resource)]
struct TurnClock {
    energy: f32,
}

fn charge(time: Res<Time>, mut clock: ResMut<TurnClock>) {
    clock.energy = (clock.energy + time.delta_secs()).min(1.0);
}

#[derive(Component)]
struct Actor {
    hp: i32,
}

fn spend(mut clock: ResMut<TurnClock>, mut actors: Query<&mut Actor>) {
    if clock.energy < 1.0 {
        return;
    }
    clock.energy = 0.0;
    for mut actor in &mut actors {
        if actor.hp > 0 {
            actor.hp -= 1;
        }
    }
}

fn install_turns(app: &mut App) {
    app.insert_resource(TurnClock { energy: 0.0 })
        .add_systems(Update, (charge, spend).chain());
}

Loot on the floor is an entity the actor can pick up by grid distance.

#[derive(Component)]
struct Loot {
    value: u32,
}

#[derive(Component)]
struct GridPos {
    x: i32,
    y: i32,
}

#[derive(Component)]
struct Actor;

#[derive(Resource)]
struct RunSeed(u64);

fn pickup(
    mut commands: Commands,
    actors: Query<&GridPos, With<Actor>>,
    loot: Query<(Entity, &GridPos, &Loot)>,
    mut wallet: ResMut<RunSeed>,
) {
    for actor in &actors {
        for (entity, pos, item) in &loot {
            if actor.x == pos.x && actor.y == pos.y {
                wallet.0 = wallet.0.wrapping_add(u64::from(item.value));
                commands.entity(entity).despawn();
            }
        }
    }
}

RunSeed in pickup is only a stand-in counter so the example stays inside one resource. A coin wallet belongs on bevy-economy-system. permadeath and spend both write Actor; chain them when both run.

Scope

• Noise and larger maps route to bevy-procedural-generation.
• Inventory stacks route to bevy-inventory-system.

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 field stored off the 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	Use the examples in this skill	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.

• Do not rebuild StdRng from a new seed each frame. WHY: the run seed stays on RunSeed so room layout stays reproducible.

• Do not let permadeath and spend both write Actor without .chain(). WHY: unordered mutable queries on the same component conflict.

• 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 latest branch.

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

• godot-genre-roguelike - Roguelike on the Godot engine, same depth.
• bevy-procedural-generation - Seed and spawn.
• bevy-turn-system - Turn order when the run is turn-based.
• bevy-inventory-system - Run loot.
• bevy-rpg-stats - Run stats.

Downstream / consumers

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

Master

• bevy-master - Bevy router.