Bevy quest system

When to use

Load this when objectives advance. Dialogue that grants them stays on bevy-dialogue-system.

ECS shape

• Components: quest id and stage you define.
• Resources: run-wide tables live in a Resource (bevy-data-resources).
• Systems: mutate those components on Update or the fixed timestep. Use .chain() when damage must land before death.
• Messages: one-shot facts (hit, pickup, quest advance) go through bevy-events-messaging. This file does not add a new event type name.

Where a quest lives

Fact	Owner
Definition	Id plus objectives in QuestCatalog.
Objective count	A number incremented from a Message.
Complete	A stage change on QuestProgress. Rewards go through inventory or economy skills.

Scope

• A quest definition is a Resource table. Runtime progress is a Component on the party entity.
• One system writes stage changes. Completion grants stay as data another skill reads.

Examples

[dependencies]
bevy = "0.20"

Definitions live in one resource. The party entity stores which quests are active and how far each objective has counted.

#[derive(Clone, Copy, PartialEq, Eq, Hash)]
struct QuestId(u32);

#[derive(Clone, Copy, PartialEq, Eq)]
enum QuestStage {
    Inactive,
    Active,
    Complete,
}

#[derive(Clone, Copy)]
struct ObjectiveDef {
    id: u32,
    required: u32,
}

struct QuestDef {
    id: QuestId,
    objectives: Vec<ObjectiveDef>,
}

#[derive(Resource)]
struct QuestCatalog {
    quests: Vec<QuestDef>,
}

#[derive(Clone, Copy)]
struct ObjectiveProgress {
    id: u32,
    count: u32,
}

#[derive(Component)]
struct QuestProgress {
    quest: QuestId,
    stage: QuestStage,
    objectives: Vec<ObjectiveProgress>,
}

fn accept(catalog: Res<QuestCatalog>, mut commands: Commands, party: Query<Entity, Without<QuestProgress>>) {
    let Some(def) = catalog.quests.first() else {
        return;
    };
    for entity in &party {
        commands.entity(entity).insert(QuestProgress {
            quest: def.id,
            stage: QuestStage::Active,
            objectives: def
                .objectives
                .iter()
                .map(|objective| ObjectiveProgress {
                    id: objective.id,
                    count: 0,
                })
                .collect(),
        });
    }
}

A pickup or kill is a message. The quest system is the only writer of QuestProgress.

#[derive(Clone, Copy, PartialEq, Eq)]
enum QuestStage {
    Active,
    Complete,
}

#[derive(Component)]
struct QuestProgress {
    stage: QuestStage,
    objective: u32,
    count: u32,
    required: u32,
}

#[derive(Message)]
struct ObjectiveFact {
    objective: u32,
}

fn apply_facts(mut facts: MessageReader<ObjectiveFact>, mut quests: Query<&mut QuestProgress>) {
    for fact in facts.read() {
        for mut quest in &mut quests {
            if quest.stage != QuestStage::Active || quest.objective != fact.objective {
                continue;
            }
            quest.count = (quest.count + 1).min(quest.required);
            if quest.count >= quest.required {
                quest.stage = QuestStage::Complete;
            }
        }
    }
}

Register the message, accept on startup, then apply facts. One system writes QuestProgress. A completed stage is the reward payload other skills read.

#[derive(Clone, Copy, PartialEq, Eq)]
enum QuestStage {
    Active,
    Complete,
}

#[derive(Component)]
struct QuestProgress {
    stage: QuestStage,
    objective: u32,
    count: u32,
    required: u32,
}

#[derive(Message)]
struct ObjectiveFact {
    objective: u32,
}

#[derive(Resource, Default)]
struct QuestCatalog;

fn accept(mut commands: Commands) {
    commands.spawn(QuestProgress {
        stage: QuestStage::Active,
        objective: 1,
        count: 0,
        required: 3,
    });
}

fn apply_facts(mut facts: MessageReader<ObjectiveFact>, mut quests: Query<&mut QuestProgress>) {
    for fact in facts.read() {
        for mut quest in &mut quests {
            if quest.stage != QuestStage::Active || quest.objective != fact.objective {
                continue;
            }
            quest.count = (quest.count + 1).min(quest.required);
            if quest.count >= quest.required {
                quest.stage = QuestStage::Complete;
            }
        }
    }
}

pub struct QuestPlugin;

impl Plugin for QuestPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<QuestCatalog>()
            .add_message::<ObjectiveFact>()
            .add_systems(Startup, accept)
            .add_systems(Update, apply_facts);
    }
}

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 outside the world
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
Quest definitions	QuestCatalog	Copying progress counts back into the catalog
Stage change	The one Update system that reads MessageReader<ObjectiveFact>	A dialogue system writing QuestProgress
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 documentation	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 keep a second writer of QuestProgress. WHY: two mutable queries of the same component race unless .chain() orders them.

• Do not import another engine's node or signal types. WHY: quest stage is a component and a message, not a foreign object.

• No invented APIs or unnamed third-party crates as the chosen solver. WHY: this skill only names documented Bevy crates and modules.

Reference

Official links stay on unversioned latest pages. The library pin on bevy-master stays 0.20.0.

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 - Hub and schedules.
• bevy-ecs-composition - Components and systems.
• bevy-dialogue-system - Lines that grant quests.
• bevy-data-resources - Tables and definitions.
• bevy-events-messaging - One-shot facts.

Complements

• bevy-state-machines - Mode flags.
• godot-quest-system - Godot package for quest tracking.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.