Window doesn't clear if I use Query<&Window> in my draw function

[jcarvajal288]

I'm having a problem where the window isn't clearing properly before each frame. I've set a clear color, and I draw a grid of sprites. When I resize the window, though, the sprite grid smears like in the image below:

Here is my code:

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .insert_resource(Images::default())
        .insert_resource(LevelMap::default())
        .add_systems(Startup, (load_images, setup, draw).chain())
        .add_systems(Update, draw)
        .run();
}

fn setup(mut commands: Commands, mut clear_color: ResMut<ClearColor>) {
    commands.spawn(Camera2dBundle::default());
    clear_color.0 = Color::hsl(211., 1., 0.8);
}

fn draw(commands: Commands, level_map: Res<LevelMap>, images: Res<Images>, windows: Query<&Window>) {
    let window_center = Vec2::new(windows.single().resolution.width() / 2., windows.single().resolution.height() / 2.);
    level_map.draw(commands, &images, window_center);
}

I've figured out that the problem is the windows parameter in my draw function. If I remove that parameter, the screen clears as I expect and there is no smearing, but I need that parameter to get the screen resolution so I can put the sprite grid at the top left like I want. How should I approach this?

Here is a link to the full code (error is on branch window-bug): https://github.com/jcarvajal288/puzzle-dungeon/tree/window-bug

[DasLixou]

Entities are persistent. You spawn new sprites in the draw system, which is in the Update schedule, being called every frame. So you create more and more tiles every frame. Moving the draw function into the Startup schedule and having another system updating their position should be the way to go.

[jcarvajal288]

Oh! Ok, so I'm not painting sprites on the screen each frame like I am in some other engines. Things are starting to make sense. Thank you.