How to rotate a Mesh2d Triangle on it's own center point?

[rmoraes92]

Hi,

So I was reading this example https://bevyengine.org/examples/2d-rendering/rotation/ and decide to try applying it to my case:

fn startup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
) {
    let rocket_size = 10.0;
    let x = 50.0;
    commands.spawn((
        RandomComponent,
        RandomComponent(0.0),
        Mesh2d(meshes.add(Triangle2d::new(
            Vec2::new(x, rocket_size),
            Vec2::new(x - rocket_size, 0.0),
            Vec2::new(x + rocket_size, 0.0),
        ))),
        MeshMaterial2d(materials.add(
            Color::hsl(360. * 255 as f32 / 255 as f32, 0.95, 0.7)
        )),
        Transform::from(x, 0.0, 0.0)
    ));
}

and the update rotation fn

fn update_rocket_angle(
    time: Res<Time>,
    keys: Res<ButtonInput<KeyCode>>,
    mut query: Query<(
        & RandomComponent,
        &mut Transform,
    )>
) {
    // Rotating Rocket Nose
    // ========================================================================
    let mut rotation_factor = 0.0;
    // let mut movement_factor = 0.0;

    if keys.pressed(KeyCode::ArrowLeft) {
        rotation_factor += 1.0;
    }

    if keys.pressed(KeyCode::ArrowRight) {
        rotation_factor -= 1.0;
    }
    for (randomComp,  mut trans) in &mut query {
        trans.rotate_z(rotation_factor * 5.0 * time.delta_secs());
    }
}

But instead of seen the triangle rotating on it's on center (like the Player's sprite on the example link) the Mesh2d Triangle is rotating around the screen origin.

what am I missing here?

Thank you for reading

[void4main]

Hi,

what does Transform::from(x, 0.0, 0.0) do?
I'm only aware of Transform::from_xyz , but I'm not a pro :-)

And how do you rotate around z? (trans.rotate_z)
In bevy 2d z should be a layer and not a rotation axis. This should shift your triangle to the foreground or background if you had more objects in the same place.

Best regards,
Frank

[rmoraes92]

Thanks for the reply. Turns out my problem was the values being passed to the Triangle2d in the Mesh2d. The correct way would be to draw the triangle using values adjusted to the origin. That way when we execute the rotation the Mesh will rotate at "his own center".