Bevy Metroidvania

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

When to use

Load this for ability-gated exploration and a map of rooms.

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. Ability flags, visited cells, and the map fog below are components plus one resource.

Examples

[dependencies]
bevy = "0.20"

Traversal is a set of flags on the player. A gate stores the flag it needs. The map stores which cells are revealed. Input, gate checks, and fog share AbilitySet and MapFog, so those systems chain.

#[derive(Clone, Copy, PartialEq, Eq)]
enum Ability {
    Dash,
    WallClimb,
    DoubleJump,
}

#[derive(Component)]
struct AbilitySet {
    owned: [bool; 3],
}

impl AbilitySet {
    fn has(&self, ability: Ability) -> bool {
        self.owned[ability as usize]
    }

    fn grant(&mut self, ability: Ability) {
        self.owned[ability as usize] = true;
    }
}

#[derive(Component)]
struct Gate {
    requires: Ability,
    open: bool,
}

#[derive(Component)]
struct MapCell {
    x: i32,
    y: i32,
    visited: bool,
}

#[derive(Resource, Default)]
struct MapFog {
    revealed: u32,
}

fn boot(mut commands: Commands) {
    commands.insert_resource(MapFog { revealed: 0 });
    commands.spawn(AbilitySet {
        owned: [false, false, false],
    });
    commands.spawn(Gate {
        requires: Ability::Dash,
        open: false,
    });
    commands.spawn(MapCell {
        x: 0,
        y: 0,
        visited: false,
    });
}

fn grant_dash(keys: Res<ButtonInput<KeyCode>>, mut players: Query<&mut AbilitySet>) {
    if !keys.just_pressed(KeyCode::KeyE) {
        return;
    }
    for mut set in &mut players {
        set.grant(Ability::Dash);
    }
}

fn open_gates(players: Query<&AbilitySet>, mut gates: Query<&mut Gate>) {
    let Some(player) = players.iter().next() else {
        return;
    };
    for mut gate in &mut gates {
        gate.open = player.has(gate.requires);
    }
}

fn reveal_cell(mut cells: Query<&mut MapCell>, mut fog: ResMut<MapFog>) {
    for mut cell in &mut cells {
        if cell.x == 0 && cell.y == 0 && !cell.visited {
            cell.visited = true;
            fog.revealed = fog.revealed.saturating_add(1);
        }
    }
}

fn install(app: &mut App) {
    app.add_systems(Startup, boot).add_systems(
        Update,
        (grant_dash, open_gates, reveal_cell).chain(),
    );
}

A shortcut opens once the player holds both dash and wall climb.

#[derive(Clone, Copy)]
enum Ability {
    Dash,
    WallClimb,
    DoubleJump,
}

#[derive(Component)]
struct AbilitySet {
    owned: [bool; 3],
}

impl AbilitySet {
    fn has(&self, ability: Ability) -> bool {
        self.owned[ability as usize]
    }
}

fn shortcut_open(players: Query<&AbilitySet>) -> bool {
    players.iter().any(|set| set.has(Ability::Dash) && set.has(Ability::WallClimb))
}

Scene shape

Piece	Bevy idiom
Genre content	Entities plus the domain skills linked below
Run-wide director	A Resource
Loop notices	bevy-events-messaging

Routing

• bevy-ability-system - Traversal abilities.
• bevy-character-movement - Motion.
• bevy-save-load - Map flags.
• bevy-mechanic-secrets - Optional rooms.

Scope

• Ability flags live on AbilitySet. Gates and visited cells are components. MapFog counts revealed cells. Bevy has no map-graph 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 script that owns the whole tree
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	Check the official docs first	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 foreign-engine 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

Official pages stay on unversioned permalinks. 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

• godot-genre-metroidvania - Peer skill for the same genre.
• bevy-ability-system - Traversal abilities.
• bevy-character-movement - Motion.
• bevy-save-load - Map flags.
• bevy-mechanic-secrets - Optional rooms.

Downstream / consumers

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

Master

• bevy-master - Bevy router.