Bevy Platform Desktop

---
name: bevy-platform-desktop
description: "Bevy ECS skill for desktop windows. Use when setting the primary window size, present mode, fullscreen, or close behavior. Keywords: Bevy, window, desktop, WindowPlugin, PrimaryWindow, WindowMode."
---

# Bevy desktop platform

## When to use

Load this when configuring the desktop window, mode, or close behavior. Web and mobile constraints stay on their skills.

## ECS shape

- **Module:** `bevy::window` is a platform-agnostic window interface. `WindowPlugin` is part of `DefaultPlugins`.
- **Components:** `Window` is the defining component for window entities. `PrimaryWindow` marks the primary window.
- **Mode:** `WindowMode`, `PresentMode`, `WindowResolution`, `WindowPosition` are enums or structs on that page.
- **Backend feature:** `bevy_winit` is the winit window and input backend. `x11` and `wayland` are features.
- **Close:** `exit_on_primary_closed` and `exit_on_all_closed` are named functions. `WindowCloseRequested` is the event.

## Coming from Godot

| Godot idea | Bevy idiom |
| --- | --- |
| Window size | `WindowResolution` on the primary `Window` |
| Fullscreen | `WindowMode::BorderlessFullscreen` |
| Quit on close | `ExitCondition::OnPrimaryClosed` on `WindowPlugin` |

## Scope

`x11` and `wayland` are `bevy` features. The primary window is configured on `WindowPlugin` before the app runs. Runtime mode changes write the `Window` component marked `PrimaryWindow`.

## Examples

```toml
[package]
name = "desktop"
version = "0.1.0"
edition = "2021"

[dependencies]
bevy = "0.20"
```

The primary window is 1280 by 720, vsync, and closes the app when that window closes.

```rust
use bevy::window::ExitCondition;
use bevy::window::PresentMode;
use bevy::window::WindowMode;
use bevy::window::WindowResolution;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins.set(WindowPlugin {
            primary_window: Some(Window {
                title: "Desktop".into(),
                resolution: WindowResolution::new(1280, 720),
                present_mode: PresentMode::AutoVsync,
                mode: WindowMode::Windowed,
                ..default()
            }),
            exit_condition: ExitCondition::OnPrimaryClosed,
            close_when_requested: true,
            ..default()
        }))
        .run();
}
```

F11 flips the primary window between windowed and borderless fullscreen on the current monitor.

```rust
use bevy::window::MonitorSelection;
use bevy::window::PrimaryWindow;
use bevy::window::WindowMode;

fn toggle_fullscreen(
    keys: Res<ButtonInput<KeyCode>>,
    mut windows: Query<&mut Window, With<PrimaryWindow>>,
) {
    if !keys.just_pressed(KeyCode::F11) {
        return;
    }
    let Ok(mut window) = windows.single_mut() else {
        return;
    };
    window.mode = if window.mode == WindowMode::Windowed {
        WindowMode::BorderlessFullscreen(MonitorSelection::Current)
    } else {
        WindowMode::Windowed
    };
}
```

A second system reads the live resolution. It does not write `Window`, so it can run beside the toggle without `.chain()`.

```rust
use bevy::window::PrimaryWindow;

fn log_resolution(windows: Query<&Window, With<PrimaryWindow>>) {
    let Ok(window) = windows.single() else {
        return;
    };
    let width = window.resolution.width();
    let height = window.resolution.height();
    let _ = (width, height);
}
```

## 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 Godot node script |
| 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](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 DisplayServer or window project-setting names. 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 Documentation
- `bevy crate` - API reference and Cargo feature list.
- [Assets](https://bevy.org/assets/) - Official asset catalog. No third-party crate was selected.
- [Examples](https://github.com/bevyengine/bevy/tree/latest/examples#examples) - Example tree on the `latest` branch.
- [ECS](https://bevy.org/learn/quick-start/getting-started/ecs/) - `Component`, systems, `Query`, `Startup`, `Update`, and `.chain()`.
- [Plugins](https://bevy.org/learn/quick-start/getting-started/plugins/) - `Plugin`, `DefaultPlugins`, `MinimalPlugins`, and `add_plugins`.
- `bevy::window` - `Window`, `WindowPlugin`, `PrimaryWindow`, `WindowMode`.

### Related Skills

#### Prerequisites
- [bevy-master](https://github.com/thedivergentai/Game-Dev-Agentic-Skills/blob/main/skills/bevy-master/SKILL.md) - Hub and schedules.
- [bevy-ecs-composition](https://github.com/thedivergentai/Game-Dev-Agentic-Skills/blob/main/skills/bevy-ecs-composition/SKILL.md) - Components and systems.

#### Complements
- [bevy-platform-web](https://github.com/thedivergentai/Game-Dev-Agentic-Skills/blob/main/skills/bevy-platform-web/SKILL.md) - Wasm limits.
- [bevy-input-handling](https://github.com/thedivergentai/Game-Dev-Agentic-Skills/blob/main/skills/bevy-input-handling/SKILL.md) - Pointer and keyboard.
- [godot-platform-desktop](https://github.com/thedivergentai/Game-Dev-Agentic-Skills/blob/main/skills/godot-platform-desktop/SKILL.md) - Equivalent Godot skill.

#### Downstream / consumers
- None yet.

#### Master
- [bevy-master](https://github.com/thedivergentai/Game-Dev-Agentic-Skills/blob/main/skills/bevy-master/SKILL.md) - Bevy router.