Simple circle transform not working [noob]

[bobfp]

Hi everyone, I just started on my Bevy journey, and got stuck quicker than I expected :/
I'm trying to get a simple circle to move across the screen, and all I get is a static circle.

use bevy::{prelude::*, sprite::MaterialMesh2dBundle};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, move_circle)
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    commands.spawn(Camera2dBundle::default());
    commands.spawn(MaterialMesh2dBundle {
        mesh: meshes.add(shape::Circle::new(50.).into()).into(),
        material: materials.add(ColorMaterial::from(Color::PURPLE)),
        transform: Transform::from_translation(Vec3::new(-150., 0., 0.)),
        ..default()
    });
}

fn move_circle(mut circle: Query<(&mut Transform)>, timer: Res<Time>) {
    for mut transform in &mut circle {
        println!("WTF {}", transform.translation);
        transform.translation.x += 150.0 * timer.delta_seconds();
    }
}

My console prints out what looks like I'd expect -- Increasing x values in the translation vector, but the circle just... sits there.

[rparrett]

Don't be discouraged. This is a pretty common beginner mistake to make. You're moving the circle, but also the camera!

To move only the circle, you can:

Create a struct that we'll use a "marker component."

#[derive(Component)]
struct Circle;

Add it to your circle when you spawn it.

commands.spawn((
    MaterialMesh2dBundle {
        mesh: meshes.add(shape::Circle::new(50.).into()).into(),
        material: materials.add(ColorMaterial::from(Color::PURPLE)),
        transform: Transform::from_translation(Vec3::new(-150., 0., 0.)),
        ..default()
    },
    Circle
));

Finally, add a query filter to your move_circle system.

fn move_circle(mut circle: Query<&mut Transform, With<Circle>>, timer: Res<Time>) { /* ... */ }

[bobfp]

Thank you so much!

[chaserileyroberts]

I made the same mistake! Glad this tip was here.