Bevy Educational (thin router)

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

When to use

Load this for prompts, answers, and progress flags.

ECS shape

• Components hold a prompt and each choice as plain data.
• Resources hold how many answers were graded and how many were correct.
• Systems select a choice, then grade it. .chain() keeps the grade after the selection.
• Schedule: gameplay mode changes go through bevy-state-machines.

[package]
name = "educational"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.20"

One prompt, two choices, one progress resource.

#[derive(Component)]
struct Prompt {
    text: String,
}

#[derive(Component)]
struct Choice {
    label: String,
    correct: bool,
    picked: bool,
    graded: bool,
}

#[derive(Resource, Default)]
struct LessonProgress {
    answered: u32,
    correct: u32,
}

fn spawn_lesson(mut commands: Commands) {
    commands.spawn(Prompt {
        text: "Which way is north?".to_string(),
    });
    commands.spawn(Choice {
        label: "Up".to_string(),
        correct: true,
        picked: false,
        graded: false,
    });
    commands.spawn(Choice {
        label: "Down".to_string(),
        correct: false,
        picked: false,
        graded: false,
    });
    commands.init_resource::<LessonProgress>();
}

fn pick_first(mut choices: Query<&mut Choice>) {
    for mut choice in &mut choices {
        if choice.correct && !choice.graded && !choice.picked {
            choice.picked = true;
            break;
        }
    }
}

fn grade(mut progress: ResMut<LessonProgress>, mut choices: Query<&mut Choice>) {
    for mut choice in &mut choices {
        if choice.picked && !choice.graded {
            progress.answered = progress.answered.saturating_add(1);
            if choice.correct {
                progress.correct = progress.correct.saturating_add(1);
            }
            choice.graded = true;
            choice.picked = false;
        }
    }
}

pub struct LessonPlugin;

impl Plugin for LessonPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, spawn_lesson)
            .add_systems(Update, (pick_first, grade).chain());
    }
}

pick_first and grade both write Choice, so they stay chained.

A readout only reads progress.

#[derive(Resource, Default)]
struct LessonProgress {
    answered: u32,
    correct: u32,
}

fn show_score(progress: Res<LessonProgress>) {
    let _answered = progress.answered;
    let _correct = progress.correct;
}

pub struct ScorePlugin;

impl Plugin for ScorePlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<LessonProgress>()
            .add_systems(Update, show_score);
    }
}

Lesson data

Need	Bevy idiom
Prompts and choices	Entities plus the domain skills linked below
Lesson totals	A Resource
One-shot loop notices	bevy-events-messaging

Routing

• bevy-ui-text - Prompts.
• bevy-ui-layout - Choices.
• bevy-save-load - Progress saves.
• bevy-state-machines - Lesson mode.

Scope

• Prompts, choices, and the progress resource are gameplay data you define. UI text and layout stay on the linked UI skills.

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 struct that stores every entity's fields
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	Read the linked Bevy pages	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 scene-tree 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 links stay on the unversioned learn pages.

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

• bevy-ui-text - Prompts.
• bevy-ui-layout - Choices.
• bevy-save-load - Progress saves.
• bevy-state-machines - Lesson mode.

Downstream / consumers

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

Master

• bevy-master - Bevy router.