Unparented UI element just floating there | Bevy | Page 1

pliant galleon Dec 16, 2023, 11:11 AM

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I have a mystery unparented UI element that is created as an unintended byproduct of another system that otherwise works smoothly. Here's the code:

Eventually this system will put an image of an item in the item slots. For now it just puts the entity id in there.

#[derive(Component)]
struct DisplayItem(Option<Entity>);

fn display_item_system(
    mut commands: Commands,
    query: Query<(Entity, &DisplayItem), Changed<DisplayItem>>,
) {
    for (entity, display_item) in query.iter() {
        commands.entity(entity).clear_children();
        if let Some(item_entity) = display_item.0 {
            println!("{:?} displaying {:?}", entity, item_entity);
            // If there is an item, display it
            commands.entity(entity).with_children(|parent| {
                parent.spawn(TextBundle::from_section(
                    format!("{:?}", item_entity),
                    TextStyle {
                        font: Default::default(),
                        font_size: 20.0,
                        color: Color::rgb(0.9, 0.9, 0.9),
                    },
                ));
            });
        }
    }
}

#

This is the system where I create the entities that have the DisplayItem components:

fn update_inventory_ui_elements(
    slot_query: Query<&InventorySlots, (With<LocalPlayer>, Or<(Changed<InventorySlots>, Added<InventorySlots>)>)>,
    slot_parent_query: Query<Entity, With<InventorySlotParent>>,
    mut commands: Commands,
) {
    if let Ok(inventory_slot_parent_entity) = slot_parent_query.get_single() {
        for slots in slot_query.iter() {
            commands.entity(inventory_slot_parent_entity).clear_children();
            for (i, slot) in slots.0.iter().enumerate() {

                //Spawn new UI elements for each slot
                let slot_entity = commands.spawn((
                    ButtonBundle {
                        style: Style {
                            justify_content: JustifyContent::FlexStart,
                            flex_direction: FlexDirection::Row,
                            margin: UiRect::all(Val::Px(2.0)),
                            ..default()
                        },
                        background_color: BackgroundColor(Color::rgba(0.15, 0.15, 0.15, 0.8)),
                        ..default()
                    },
                    InventorySlotMap(i),
                    DisplayItem(*slot),
                )).id();

                // Add the newly created slot UI element to the parent entity
                commands.entity(inventory_slot_parent_entity).add_child(slot_entity);
            }
        }
    } else {
        eprintln!("InventorySlotParent entity not found");
    }
}

#

Attached is a gif of these systems in action. As you can see there is an unparented display for one of the selected items in the top left. Since it's theoretically the only unparented DisplayItem entity, I tried deleting it with the following system:

#

fn clean_up_system(
    kill_me: Query<Entity, (Without<Parent>, With<DisplayItem>)>,
    mut commands: Commands,
) {
    for entity in kill_me.iter() {
        commands.entity(entity).despawn();
    }
}

This system causes a crash when I click on an item (i.e., when the rogue DisplayItem entity would normally appear). The error is as follows:

thread 'Compute Task Pool (1)' panicked at C:\Users\willi\.cargo\registry\src\index.crates.io-6f17d22bba15001f\taffy-0.3.18\src\node.rs:246:29:
invalid SlotMap key used
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Encountered a panic in system `bevy_ui::layout::ui_layout_system`!
Encountered a panic in system `bevy_app::main_schedule::Main::run_main`!
error: process didn't exit successfully: `target\debug\demiurge.exe` (exit code: 101)

pliant galleon Dec 16, 2023, 11:31 AM

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This all seems very strange to me. I only use DisplayItem in 2 places, and in both the entity is created with a parent so this should be impossible

light warren Dec 16, 2023, 11:31 AM

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You probably could fix that by filtering the entity in the system where you update the display, But that doesn't solve the problem of where the system is created.

pliant galleon Dec 16, 2023, 11:33 AM

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light warren You probably could fix that by filtering the entity in the system where you upda...

I don't understand. Filtering which entity? What kind of filter?

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Like only update the display if the display entity has a parent?

light warren Dec 16, 2023, 11:34 AM

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pliant galleon I don't understand. Filtering which entity? What kind of filter?

well, the same way you tried to filter the entity in the cleanup system

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my guess: the problem is that the entity at fault has a DisplayItem, when you use Changed<DisplayItem>, the system detects another entity that has Changed somehow (the ghost entity)

pliant galleon Dec 16, 2023, 11:37 AM

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I'll give it a shot

light warren Dec 16, 2023, 11:44 AM

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Btw, other thing that is bugging me is that the problem only happen when you click Removing the entity from a slot. Maybe you should give a look at the system that do that

pliant galleon Dec 16, 2023, 5:44 PM

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So strange. I've confirmed this rogue UI element doesn't have a Parent component, but adding Without<Parent> to my display_item_system does nothing.

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Here's the code that governs adding and removing an item from a slot:

fn try_select_inventory_slot_system(
    mut selected_query: Query<(
        &mut SelectedItem,
        &mut InventorySlots,
    )>,
    mut select_events: EventReader<SelectedInventorySlot>,
) {
    for event in select_events.iter() {
        for (mut selected_item, mut inventory_slots) in selected_query.iter_mut() {
            if selected_item.0.is_some() {
                let selected_item_entity = selected_item.0.unwrap();

                let slot_item_entity = match inventory_slots.0.get_mut(event.0) {
                    Some(slot) => slot.take(),
                    None => None,
                };

                if let Some(slot) = inventory_slots.0.get_mut(event.0) {
                    *slot = Some(selected_item_entity);
                }

                selected_item.0 = slot_item_entity;
            } else {
                if let Some(slot) = inventory_slots.0.get_mut(event.0) {
                    selected_item.0 = slot.take();
                }
            }
        }
    }
}

light warren Dec 16, 2023, 6:29 PM

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pliant galleon This is the system where I create the entities that have the DisplayItem compone...

Just to be sure, does this system recreate all the slots when try_select_inventory_slot_system() run?
The behavior of the ghost slot is extremely interesting. It even appears that the entity was not cleaned correctly, lost its parents and went to the corner of the screen. (judging by the gif that you gave)

ionic ferry Dec 16, 2023, 7:21 PM

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I haven't read the convo yet but you should avoid using despawn and instead always use despawn_recursive.
despawn doesn't handle child/parent entities properly.

pliant galleon Dec 16, 2023, 7:36 PM

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ionic ferry I haven't read the convo yet but you should avoid using `despawn` and instead al...

I use .clear_children(), I don't use .despawn() anywhere.

ionic ferry Dec 16, 2023, 7:41 PM

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The clean_up_system you messaged above thats causing the crash uses despawn

pliant galleon Dec 16, 2023, 7:44 PM

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light warren Just to be sure, does this system recreate all the slots when try\_select\_inven...

There are 4 systems which govern the inventories behavior.

update_inventory_ui_elements detects when InventorySlots (the component that holds the actual entity data about the inventory) changes. When it changes it uses .clear_children() to despawn all the current buttons and makes new ones in their place.

click_inventory_slot_system detects Interaction::Pressed events on any button with an InventorySlotMap component and fires an event.

try_select_inventory_slot_system detects those events and puts the currently selected item into the clicked slot, and makes the item in the slot the currently selected item (swaps them around basically)

and finally the display_item_system which gets any entity with a changed DisplayItem component and re-displays it.

So... yes. update_inventory_ui_elements will detect the changes made in try_select_inventory_slot_system and will remake all the buttons.

pliant galleon Dec 16, 2023, 7:44 PM

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ionic ferry The `clean_up_system` you messaged above thats causing the crash uses `despawn`

Ah, silly me. That system was just for debugging. I suppose I could try it again with despawn_recursive to see if it works. I guess that's at least a bandaid... I'd like to understand why this is happening though.

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Here's the new system as per your advice.

fn clean_up_system(
    kill_me: Query<Entity, (Without<Parent>, With<DisplayItem>)>,
    mut commands: Commands,
) {
    for entity in kill_me.iter() {
        commands.entity(entity).despawn_recursive();
    }
}

When I click on an item (thus causing the rogue entity to appear) it causes this crash:

thread 'Compute Task Pool (5)' panicked at C:\Users\willi\.cargo\registry\src\index.crates.io-6f17d22bba15001f\taffy-0.3.18\src\node.rs:246:29:
invalid SlotMap key used
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Encountered a panic in system `bevy_ui::layout::ui_layout_system`!
Encountered a panic in system `bevy_app::main_schedule::Main::run_main`!
error: process didn't exit successfully: `target\debug\demiurge.exe` (exit code: 101)

ionic ferry Dec 16, 2023, 7:46 PM

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Maybe you meant to use .despawn_descendants() instead of .clear_children()?

pliant galleon Dec 16, 2023, 7:48 PM

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ionic ferry Maybe you meant to use `.despawn_descendants()` instead of `.clear_children()`?

This was it.

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Thanks so much everyone!

light warren Dec 16, 2023, 7:49 PM

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So the problem was in fact the despawn

pliant galleon Dec 16, 2023, 7:49 PM

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So does clear children just free the children?

light warren Dec 16, 2023, 7:49 PM

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Good to know

pliant galleon Dec 16, 2023, 7:49 PM

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light warren So the problem was in fact the despawn

Yeah 😅

light warren Dec 16, 2023, 7:52 PM

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pliant galleon So does clear children just free the children?

Apparently Clear Children doesn't despawn the children, but just remove their parent and remove the parent Children component

pliant galleon Dec 16, 2023, 7:53 PM

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That makes sense I suppose. Good to know...

#Unparented UI element just floating there