bevy/examples/window/scale_factor_override.rs

use bevy::prelude::*;

/// This example illustrates how to customize the default window settings
fn main() {
    App::build()
        .insert_resource(WindowDescriptor {
            width: 500.,
            height: 300.,
            ..Default::default()
        })
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup.system())
        .add_system(toggle_override.system())
        .add_system(change_scale_factor.system())
        .run();
}

fn setup(
    commands: &mut Commands,
    asset_server: Res<AssetServer>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    commands
        // ui camera
        .spawn(UiCameraBundle::default())
        // root node
        .spawn(NodeBundle {
            style: Style {
                size: Size::new(Val::Percent(100.0), Val::Percent(100.0)),
                justify_content: JustifyContent::SpaceBetween,
                ..Default::default()
            },
            material: materials.add(Color::NONE.into()),
            ..Default::default()
        })
        .with_children(|parent| {
            parent
                // left vertical fill (border)
                .spawn(NodeBundle {
                    style: Style {
                        size: Size::new(Val::Px(200.0), Val::Percent(100.0)),
                        border: Rect::all(Val::Px(2.0)),
                        ..Default::default()
                    },
                    material: materials.add(Color::rgb(0.65, 0.65, 0.65).into()),
                    ..Default::default()
                })
                .with_children(|parent| {
                    parent.spawn(TextBundle {
                        style: Style {
                            align_self: AlignSelf::FlexEnd,
                            ..Default::default()
                        },
                        text: Text::with_section(
                            "Example text",
                            TextStyle {
                                font: asset_server.load("fonts/FiraSans-Bold.ttf"),
                                font_size: 30.0,
                                color: Color::WHITE,
                            },
                            Default::default(),
                        ),
                        ..Default::default()
                    });
                });
        });
}

/// This system toggles scale factor overrides when enter is pressed
fn toggle_override(input: Res<Input<KeyCode>>, mut windows: ResMut<Windows>) {
    let window = windows.get_primary_mut().unwrap();
    if input.just_pressed(KeyCode::Return) {
        window.set_scale_factor_override(window.scale_factor_override().xor(Some(1.)));
    }
}

/// This system changes the scale factor override when up or down is pressed
fn change_scale_factor(input: Res<Input<KeyCode>>, mut windows: ResMut<Windows>) {
    let window = windows.get_primary_mut().unwrap();
    if input.just_pressed(KeyCode::Up) {
        window.set_scale_factor_override(window.scale_factor_override().map(|n| n + 1.));
    } else if input.just_pressed(KeyCode::Down) {
        window.set_scale_factor_override(window.scale_factor_override().map(|n| (n - 1.).max(1.)));
    }
}