Bevy Adapt Desktop To Mobile Skill for Cursor

Bevy adapt desktop to mobile

When to use

Load this when a desktop window game must accept touch and a smaller layout. Platform features are on bevy-platform-mobile.

ECS shape

• Input: Touches lists active contacts. Action mapping lives on bevy-input-handling.
• UI: enlarge Node hit targets and pad the root with a safe-inset Resource. WindowResolution sets the logical size and an optional scale-factor override. WindowScaleFactorChanged reports a live dpi change.
• Textures: ASTC is a compressed texture format for mobile GPUs. Upload still goes through Assets<Image>.

fn configure_window(mut windows: Query<&mut Window>) {
    let Ok(mut window) = windows.single_mut() else {
        return;
    };
    window.resolution.set(720.0, 1280.0);
    window.resolution.set_scale_factor_override(Some(2.0));
}

#[derive(Resource, Default)]
struct LastTouch(Option<Vec2>);

fn track_touch(touches: Res<Touches>, mut last: ResMut<LastTouch>) {
    last.0 = touches.iter().next().map(|touch| touch.position());
}

#[derive(Component)]
struct TouchTarget;

#[derive(Component)]
struct HudRoot;

#[derive(Resource)]
struct SafeInsets {
    top: f32,
    bottom: f32,
}

fn enlarge_targets(mut nodes: Query<&mut Node, With<TouchTarget>>) {
    for mut node in &mut nodes {
        node.min_width = Val::Px(88.0);
        node.min_height = Val::Px(88.0);
    }
}

fn pad_hud(insets: Res<SafeInsets>, mut roots: Query<&mut Node, With<HudRoot>>) {
    for mut node in &mut roots {
        node.padding = UiRect {
            top: Val::Px(insets.top),
            bottom: Val::Px(insets.bottom),
            left: Val::Px(12.0),
            right: Val::Px(12.0),
        };
    }
}

use bevy::window::WindowScaleFactorChanged;

fn follow_dpi(
    mut scale_events: MessageReader<WindowScaleFactorChanged>,
    mut ui_scale: ResMut<UiScale>,
) {
    for event in scale_events.read() {
        ui_scale.0 = event.scale_factor as f32;
    }
}

[dependencies]
bevy = "0.20"

Adapt choices

| Need | Bevy approach |

| --- | --- |

| Pointer | Touches for contacts. Pointer position on a desktop window is Window::cursor_position. |

| Hover-only menus | Actions that require a hover state need a pressed or tapped path as well. |

| Safe margins | SafeInsets resource applied as Node padding. |

Scope

• Store listings and OS permission dialogs are outside this skill. Layout, touch, and dpi live in the systems above.
• Platform packaging stays on bevy-platform-mobile.

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 script field copied onto 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 export-preset or touch-emulation names in Bevy code. WHY: Touches, Window, and UiScale are the documented Bevy pieces.
• 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 links stay on bevy.org. 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-platform-mobile - Android and touch features.
• bevy-ui-layout - Reflow the HUD.

Complements

• bevy-adapt-mobile-to-desktop - The reverse adapt.
• godot-adapt-desktop-to-mobile - Same topic on the Godot track.

Downstream / consumers

• None yet.

Master

• bevy-master - Bevy router.