Bevy Puzzle

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

When to use

Load this for grid rules and an undo stack you own.

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. Grid tiles and the undo stack below are components plus one resource.

Examples

[dependencies]
bevy = "0.20"

Each tile stores a grid coordinate and whether it is a goal. The undo stack is a resource of prior coordinates. Read input, push history, then slide. Those systems share Tile, so they chain.

#[derive(Clone, Copy)]
struct GridPos {
    x: i32,
    y: i32,
}

#[derive(Component)]
struct Tile {
    pos: GridPos,
    goal: bool,
}

#[derive(Component)]
struct PlayerToken;

#[derive(Resource, Default)]
struct UndoStack {
    steps: Vec<GridPos>,
}

fn boot(mut commands: Commands) {
    commands.insert_resource(UndoStack { steps: Vec::new() });
    commands.spawn((
        PlayerToken,
        Tile {
            pos: GridPos { x: 0, y: 0 },
            goal: false,
        },
    ));
    commands.spawn(Tile {
        pos: GridPos { x: 2, y: 0 },
        goal: true,
    });
}

fn read_move(keys: Res<ButtonInput<KeyCode>>) -> GridPos {
    if keys.just_pressed(KeyCode::ArrowRight) {
        GridPos { x: 1, y: 0 }
    } else if keys.just_pressed(KeyCode::ArrowLeft) {
        GridPos { x: -1, y: 0 }
    } else if keys.just_pressed(KeyCode::ArrowUp) {
        GridPos { x: 0, y: 1 }
    } else if keys.just_pressed(KeyCode::ArrowDown) {
        GridPos { x: 0, y: -1 }
    } else {
        GridPos { x: 0, y: 0 }
    }
}

fn push_undo(
    keys: Res<ButtonInput<KeyCode>>,
    players: Query<&Tile, With<PlayerToken>>,
    mut undo: ResMut<UndoStack>,
) {
    if keys.just_pressed(KeyCode::KeyZ) {
        return;
    }
    let delta = read_move(keys);
    if delta.x == 0 && delta.y == 0 {
        return;
    }
    if let Some(tile) = players.iter().next() {
        undo.steps.push(tile.pos);
    }
}

fn slide_player(
    keys: Res<ButtonInput<KeyCode>>,
    mut players: Query<&mut Tile, With<PlayerToken>>,
) {
    if keys.just_pressed(KeyCode::KeyZ) {
        return;
    }
    let delta = read_move(keys);
    for mut tile in &mut players {
        tile.pos.x += delta.x;
        tile.pos.y += delta.y;
    }
}

fn undo_move(
    keys: Res<ButtonInput<KeyCode>>,
    mut undo: ResMut<UndoStack>,
    mut players: Query<&mut Tile, With<PlayerToken>>,
) {
    if !keys.just_pressed(KeyCode::KeyZ) {
        return;
    }
    let Some(prev) = undo.steps.pop() else {
        return;
    };
    for mut tile in &mut players {
        tile.pos = prev;
    }
}

fn install(app: &mut App) {
    app.add_systems(Startup, boot).add_systems(
        Update,
        (undo_move, push_undo, slide_player).chain(),
    );
}

The puzzle is solved when the player token shares a cell with a goal tile.

#[derive(Clone, Copy, PartialEq, Eq)]
struct GridPos {
    x: i32,
    y: i32,
}

#[derive(Component)]
struct Tile {
    pos: GridPos,
    goal: bool,
}

#[derive(Component)]
struct PlayerToken;

fn solved(players: Query<&Tile, With<PlayerToken>>, goals: Query<&Tile>) -> bool {
    let Some(player) = players.iter().next() else {
        return false;
    };
    goals.iter().any(|tile| tile.goal && tile.pos == player.pos)
}

push_undo and slide_player both call read_move, which reads ButtonInput twice in one frame. just_pressed stays true for the frame, so both see the same key.

Scene shape

Routing

• bevy-state-machines - Solve state.
• bevy-input-handling - Moves.
• bevy-data-resources - Rule tables.
• bevy-ui-layout - Hints.

Scope

• Tiles store GridPos. UndoStack keeps prior player coordinates. Bevy has no puzzle-grid 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

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 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-puzzle - Peer skill for the same genre.
• bevy-state-machines - Solve state.
• bevy-input-handling - Moves.
• bevy-data-resources - Rule tables.
• bevy-ui-layout - Hints.

Downstream / consumers

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

Master

• bevy-master - Bevy router.