The `GlobalTransform` did not get updated when `Parent` was removed

[vby]

What problem does this solve or what need does it fill?

The GlobalTransform did not get updated (it should be) when Parent was removed.

What solution would you like?

• Always recalculate the new GlobalTransform then set_if_neq.

if transform_changed {
    *global_transform = GlobalTransform::from(*transform);
} else {
    global_transform.set_if_neq(GlobalTransform::from(*transform));
}

• Or use RemovedComponents<Parent>, which may have poor performance if there have so many entities without Transform.

• Or use Removed change detection, but does not exist currently.

Query<(&Transform, &mut GlobalTransform, Removed<Parent>)>

if parent_removed || transform_changed {
  *global_transform = GlobalTransform::from(*transform);
}

What alternative(s) have you considered?

none

Additional context

none

[nicopap]

Bevy 0.10 will have new commands to update parent while updating the transform, see

• [Merged by Bors] - Add an extension trait to EntityCommands to update hierarchy while preserving GlobalTransform #7024
• [Merged by Bors] - Add a reparented_to method to GlobalTransform #7020

[nicopap]

I may have misunderstood the issue. Could you provide a minimal reproducible example or at least try with the last main commit? It might have been fixed with a recent commit.

• [Merged by Bors] - Improve change detection behavior for transform propagation #6870

[vby]

I may have misunderstood the issue. Could you provide a minimal reproducible example or at least try with the last main commit? It might have been fixed with a recent commit.

• [Merged by Bors] - Improve change detection behavior for transform propagation #6870

Here is a simple test case for this.

#[test]
fn correct_parent_removed() {
    ComputeTaskPool::init(TaskPool::default);
    let mut world = World::default();

    let mut update_stage = SystemStage::parallel();
    update_stage.add_system(sync_simple_transforms);
    update_stage.add_system(propagate_transforms);

    let mut schedule = Schedule::default();
    schedule.add_stage(Update, update_stage);

    let (root, parent, child) = {
        let mut command_queue = CommandQueue::default();
        let mut commands = Commands::new(&mut command_queue, &world);
        let root = commands.spawn(TransformBundle::from_transform(Transform::from_xyz(1.0, 0.0, 0.0))).id();
        let parent = commands.spawn(TransformBundle::IDENTITY).id();
        let child = commands.spawn(TransformBundle::IDENTITY).id();
        commands.entity(parent).set_parent(root);
        commands.entity(child).set_parent(parent);
        command_queue.apply(&mut world);
        schedule.run(&mut world);
        (root, parent, child)
    };

    assert_ne!(
        world.get::<GlobalTransform>(parent).unwrap(),
        &GlobalTransform::from(Transform::IDENTITY)
    );

    // Remove parent of `parent`
    {
        let mut command_queue = CommandQueue::default();
        let mut commands = Commands::new(&mut command_queue, &world);
        commands.entity(parent).remove_parent();
        command_queue.apply(&mut world);
        schedule.run(&mut world);
    }

    assert_eq!(
        world.get::<GlobalTransform>(parent).unwrap(),
        &GlobalTransform::from(Transform::IDENTITY)
    );
}

[nicopap]

yeah I can reproduce. I've a fix working, I'll open a PR shortly