Bevy Tilemap Agent Skill

Bevy tilemap

When to use

Load this before storing a grid of tiles. Bevy draws cells with Sprite and a TextureAtlas. The grid itself is a resource and a set of entities you own.

ECS shape

• Resource: TileGrid owns width, height, and one cell id per slot.
• Component: TileCell stores the grid coordinate on the sprite entity.
• Draw: TextureAtlasLayout::from_grid slices a sheet. Sprite::from_atlas_image picks a cell index.
• Schedule: spawn the grid in Startup. Autotile rules are a plain function over neighbor ids.

Examples

[dependencies]
bevy = "0.20"

The grid is the source of truth. Sprites are a view of it.

#[derive(Resource)]
struct TileGrid {
    width: i32,
    height: i32,
    cells: Vec<u16>,
}

impl TileGrid {
    fn index(&self, x: i32, y: i32) -> Option<usize> {
        if x < 0 || y < 0 || x >= self.width || y >= self.height {
            return None;
        }
        Some((y * self.width + x) as usize)
    }

    fn get(&self, x: i32, y: i32) -> u16 {
        self.index(x, y).map(|i| self.cells[i]).unwrap_or(0)
    }
}

#[derive(Component)]
struct TileCell {
    x: i32,
    y: i32,
}

A 4 by 4 sheet of 16-pixel tiles becomes one layout asset. Each solid cell spawns a sprite.

#[derive(Resource)]
struct TileGrid {
    width: i32,
    height: i32,
    cells: Vec<u16>,
}

impl TileGrid {
    fn get(&self, x: i32, y: i32) -> u16 {
        if x < 0 || y < 0 || x >= self.width || y >= self.height {
            return 0;
        }
        self.cells[(y * self.width + x) as usize]
    }
}

#[derive(Component)]
struct TileCell {
    x: i32,
    y: i32,
}

fn spawn_tiles(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut layouts: ResMut<Assets<TextureAtlasLayout>>,
    grid: Res<TileGrid>,
) {
    let layout = layouts.add(TextureAtlasLayout::from_grid(
        UVec2::splat(16),
        4,
        4,
        None,
        None,
    ));
    let image = asset_server.load("tiles.png");
    let tile = 16.0;
    for y in 0..grid.height {
        for x in 0..grid.width {
            let id = grid.get(x, y);
            if id == 0 {
                continue;
            }
            commands.spawn((
                Sprite::from_atlas_image(
                    image.clone(),
                    TextureAtlas {
                        layout: layout.clone(),
                        index: id as usize,
                    },
                ),
                Transform::from_xyz(x as f32 * tile, y as f32 * tile, 0.0),
                TileCell { x, y },
            ));
        }
    }
    commands.spawn(Camera2d);
}

Four-neighbor bits pick an atlas index. Empty neighbors stay zero.

#[derive(Resource)]
struct TileGrid {
    width: i32,
    height: i32,
    cells: Vec<u16>,
}

impl TileGrid {
    fn get(&self, x: i32, y: i32) -> u16 {
        if x < 0 || y < 0 || x >= self.width || y >= self.height {
            return 0;
        }
        self.cells[(y * self.width + x) as usize]
    }
}

#[derive(Component)]
struct TileCell {
    x: i32,
    y: i32,
}

fn autotile_index(grid: &TileGrid, x: i32, y: i32) -> usize {
    let solid = |nx: i32, ny: i32| u16::from(grid.get(nx, ny) != 0);
    let mask = solid(x, y + 1)
        | (solid(x + 1, y) << 1)
        | (solid(x, y - 1) << 2)
        | (solid(x - 1, y) << 3);
    mask as usize
}

fn repaint(grid: Res<TileGrid>, mut tiles: Query<(&TileCell, &mut Sprite)>) {
    for (cell, mut sprite) in &mut tiles {
        if let Some(atlas) = sprite.texture_atlas.as_mut() {
            atlas.index = autotile_index(&grid, cell.x, cell.y);
        }
    }
}

Same job, Bevy types

| Design | Bevy idiom |

| --- | --- |

| TileSet atlas | TextureAtlasLayout::from_grid plus Sprite::from_atlas_image |

| TileMap layer | TileGrid resource and one entity per visible cell |

| Autotile | A function from neighbor ids to an atlas index |

Scope

There is no engine tilemap type. Collision from the grid is a physics concern on bevy-physics-2d. Streaming a larger world means spawning and despawning TileCell entities from the same resource.

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 scene-tree script hung on the entity |

| 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 | Check the official docs first | 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 Godot TileMap or TileSet types. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.
• No named tilemap crate as the chosen solution. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No Godot types in Bevy code. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.
• No invented APIs or unnamed third-party crates as the chosen solver. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

Official pages stay on unversioned bevy.org URLs. The library pin on bevy-master stays 0.20.0. Cells draw with Sprite and TextureAtlas. There is no engine tile-map type.

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-procedural-generation - Seeded layouts.
• bevy-data-resources - Map resource.

Complements

• godot-tilemap-mastery - Equivalent Godot skill.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.