changing_the_window_after_initialization.md

Changing The Window After Initialization

When we add the DefaultPlugins, it adds the WindowPlugin to our App. The WindowPlugin contains a Window struct that defines the appearance of our window. The Window can be changed even the WindowPlugin has been initialized.

To change the window, we can query the Window in a system.

use bevy::{
    app::{App, PostStartup},
    ecs::system::Query,
    window::{Window, WindowPosition},
    DefaultPlugins,
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(PostStartup, change_window)
        .run();
}

fn change_window(mut windows: Query<&mut Window>) {
    let mut window = windows.single_mut();

    window.title = "A Bevy App".into();
    window.position = WindowPosition::At((0, 0).into());
    window.resolution = (200., 100.).into();
}

We schedule the change_window system on PostStartup for simplicity. The system can also be called anytime later, such as key inputs or timers.

We use windows.single_mut() to get the Window because we are sure that there is exactly one window here.

Result:

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