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

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.

[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

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

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.