Bevy Action RPG (thin router)

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

When to use

Load this to route an action RPG: real-time hits, stats, inventory, and quests.

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.

Engine counterparts

Godot idea	Bevy idiom
Genre scene tree	Entities plus the domain skills linked below
Autoload director	A resource, not a singleton node
Signal bus for the loop	bevy-events-messaging

Routing

• bevy-character-movement - Actor motion.
• bevy-combat-system - Hits.
• bevy-rpg-stats - Attributes.
• bevy-inventory-system - Gear.
• bevy-quest-system - Objectives.
• bevy-ability-system - Casts.

Scope

This router shows the ECS joins an action RPG uses. Stats, hits, gear, and quests stay in the domain skills linked above. Hit volumes belong with the physics skills.

Join	Owner	Schedule
Incoming damage amount	Component on the actor, removed after it is applied	Update, apply then clear with .chain()
Reach and stamina	Components on the actor	Read by the ability skill; this router only spawns them
Slain count	One resource	Update, after the hit system
Gear id	Component on the actor	Inventory skill writes it; do not also write it from combat

[dependencies]
bevy = "0.20"

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

#[derive(Component)]
struct IncomingHit {
    amount: i32,
}

fn apply_hits(mut actors: Query<(&mut Vitality, &IncomingHit)>) {
    for (mut vitality, hit) in &mut actors {
        vitality.hp = (vitality.hp - hit.amount).max(0);
    }
}

fn clear_hits(mut commands: Commands, hits: Query<Entity, With<IncomingHit>>) {
    for entity in &hits {
        commands.entity(entity).remove::<IncomingHit>();
    }
}

pub struct ActionHitPlugin;

impl Plugin for ActionHitPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Update, (apply_hits, clear_hits).chain());
    }
}

#[derive(Component)]
struct GearSlot {
    item_id: Option<u32>,
}

#[derive(Resource, Default)]
struct QuestFlags {
    slain: u32,
    need: u32,
}

fn equip(mut slots: Query<&mut GearSlot>) {
    for mut slot in &mut slots {
        if slot.item_id.is_none() {
            slot.item_id = Some(1);
        }
    }
}

fn note_kill(mut flags: ResMut<QuestFlags>) {
    if flags.slain < flags.need {
        flags.slain += 1;
    }
}

pub struct ActionProgressPlugin;

impl Plugin for ActionProgressPlugin {
    fn build(&self, app: &mut App) {
        app.insert_resource(QuestFlags { slain: 0, need: 3 })
            .add_systems(Update, (equip, note_kill));
    }
}

#[derive(Component)]
struct Actor;

#[derive(Component)]
struct MeleeReach(f32);

#[derive(Component)]
struct Stamina {
    current: f32,
    max: f32,
}

fn spawn_actor(mut commands: Commands) {
    commands.spawn((
        Actor,
        MeleeReach(1.5),
        Stamina {
            current: 100.0,
            max: 100.0,
        },
        Transform::default(),
    ));
}

pub struct ActionRpgPlugin;

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

fn main() {
    App::new()
        .add_plugins(MinimalPlugins)
        .add_plugins(ActionRpgPlugin)
        .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

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 Godot node script
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 this skill	Load the skill that owns it	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 clear IncomingHit in parallel with the system that reads it. WHY: both mutably touch that component, so the clear must be .chain()ed after the apply.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• No Godot 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

The library pin on bevy-master stays 0.20.0. Official pages stay on the unversioned site.

Official Documentation

• ECS - Component, systems, Query, Startup, Update, and .chain().
• Plugins - Plugin, DefaultPlugins, MinimalPlugins, and add_plugins.
• Examples - Example tree on the latest branch.

Related Skills

Prerequisites

• bevy-master - ECS ownership and schedules.
• bevy-ecs-composition - Spawn and query shape.

Complements

• godot-genre-action-rpg - Equivalent Godot skill.
• bevy-character-movement - Actor motion.
• bevy-combat-system - Hits.
• bevy-rpg-stats - Attributes.
• bevy-inventory-system - Gear.
• bevy-quest-system - Objectives.
• bevy-ability-system - Casts.

Downstream / consumers

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

Master

• bevy-master - Bevy router.