ui: Buggy 'natural' item dragging

- Items are now placed relative to cursor instead of upper left corner
- Bug: after item drop all hovered slots are cleared and you cannot drag
  and drop item right away

src/inventory/ui.rs

@@ -27,7 +27,10 @@ pub struct UiItem(pub Entity);
 pub struct HoveredItem;
 
 #[derive(Component, Reflect)]
-pub struct DraggedItem(pub Item);
+pub struct HoveredSlot;
+
+#[derive(Component, Reflect)]
+pub struct DraggedItem(pub Item, pub UVec2);
 
 fn ui_item_node_data(item: &Item) -> (Val, Val, Val, Val, UiTransform) {
     match item.rotated {
@@ -63,9 +66,21 @@ fn reset_slots_colors(query: Query<&mut ImageNode, With<UiInventorySlot>>) {
     }
 }
 
-fn on_slot_over(e: On<Pointer<Over>>, mut query: Query<&mut ImageNode, With<UiInventorySlot>>) {
-    if let Ok(mut image) = query.get_mut(e.event_target()) {
+fn on_slot_over(
+    e: On<Pointer<Over>>,
+    mut commands: Commands,
+    mut image_query: Query<&mut ImageNode, With<UiInventorySlot>>,
+    hovered_slots: Query<Entity, With<HoveredSlot>>,
+    has_dragged_item: Option<Single<(), With<DraggedItem>>>,
+) {
+    if let Ok(mut image) = image_query.get_mut(e.event_target()) {
         image.color = Color::WHITE.darker(0.3);
+    };
+    for slot_id in hovered_slots {
+        commands.entity(slot_id).remove::<HoveredSlot>();
+    }
+    if has_dragged_item.is_none() {
+        commands.entity(e.event_target()).insert(HoveredSlot);
     }
 }
 
@@ -104,13 +119,19 @@ fn on_item_drag_start(
     mut commands: Commands,
     ui_query: Query<&UiItem, With<HoveredItem>>,
     item_query: Query<&Item>,
+    hovered_slot: Single<&UiInventorySlot, With<HoveredSlot>>
 ) {
     if let Ok(ui_item) = ui_query.get(e.event_target()) {
         let Ok(item) = item_query.get(ui_item.0) else {
             error!("UiItem {} is pointing to non-existing Item", e.event_target());
             return;
         };
-        commands.entity(e.event_target()).insert(DraggedItem(item.clone()));
+        let Some(item_position) = item.position else {
+            return;
+        };
+        let slot_position = hovered_slot.0;
+        let diff = slot_position - item_position;
+        commands.entity(e.event_target()).insert(DraggedItem(item.clone(), diff));
     }
 }
 
@@ -138,6 +159,7 @@ fn on_item_drag_drop(
     ui_inventory_query: Query<&UiInventory>,
     mut item_query: Query<&mut Item>,
     slot_query: Query<(&ChildOf, &UiInventorySlot, Option<&Children>)>,
+    slot_id_query: Query<(Entity, &UiInventorySlot, &ChildOf), With<UiInventorySlot>>,
     inventory_query: Query<(&Inventory, Option<&Children>)>,
 ) {
     let Ok((ui_item_entity, UiItem(item_entity), mut dragged_item, node, ui_transform)) = ui_item_query.get_mut(event.dropped) else {
@@ -161,16 +183,25 @@ fn on_item_drag_drop(
         None => &[],
     };
     
+    let actual_position = new_position.as_ivec2() - dragged_item.1.as_ivec2();
+    info!("{actual_position:?}");
     let temp_item = &mut dragged_item.0;
-    temp_item.position = Some(*new_position);
+    if actual_position.is_negative_bitmask() == 0 {
+        temp_item.position = Some(actual_position.as_uvec2());
+    }
+
+    let Some((slot_id, _, _)) = slot_id_query.iter().find(|(_, slot_pos, slot_parent_id)| slot_pos.0 == temp_item.position.unwrap() && slot_parent_id == &slot_parent) else {
+        return;
+    };
 
     if inventory.can_replace(item_query.as_readonly(), items, *item_entity, temp_item) {
         let mut item = item_query.get_mut(*item_entity).unwrap();
         item.position = temp_item.position;
         item.size = temp_item.size;
         item.rotated = temp_item.rotated;
-        commands.entity(ui_item_entity).insert(ChildOf(event.event_target()));
+        commands.entity(ui_item_entity).insert(ChildOf(slot_id));
         commands.entity(*item_entity).insert(ChildOf(*inventory_id));
+        commands.entity(slot_id).insert(HoveredSlot);
         update_ui_node(item.as_ref(), node, ui_transform);
     } else {
         if let Ok(item) = item_query.get(*item_entity) {
@@ -202,6 +233,7 @@ pub fn on_ui_rotate(
         let (was_rotated, item) = match maybe_dragged {
             Some(mut temp_item) => {
                 temp_item.0.rotate();
+                temp_item.1 = uvec2(temp_item.1.y, temp_item.1.x);
                 (true, Some(temp_item.0.clone()))
             },
             None => {

src/tests.rs

@@ -198,7 +198,7 @@ mod inventory {
         inventory_query: Query<(&Inventory, &Children)>,
     ) {
         let (inventory, children) = inventory_query.single().unwrap();
-        let (replacable_id, DraggedItem(replacing_item), RotatingMarker(assertion)) = replacable_item.single()
+        let (replacable_id, DraggedItem(replacing_item, _), RotatingMarker(assertion)) = replacable_item.single()
             .unwrap();
         if *assertion {
             assert!(inventory.can_replace(item_query, children, replacable_id, replacing_item));
@@ -369,7 +369,7 @@ mod inventory {
         let system = world.register_system(replace_item);
 
         world.spawn(inventory())
-            .with_child((item_a(), DraggedItem(item_c()), RotatingMarker(true)))
+            .with_child((item_a(), DraggedItem(item_c(), UVec2::ZERO), RotatingMarker(true)))
             .with_child(item_b())
             .with_child(item_d());
 
@@ -383,7 +383,7 @@ mod inventory {
         let system = world.register_system(replace_item);
 
         world.spawn(inventory())
-            .with_child((item_a(), DraggedItem(item_c()), RotatingMarker(false)))
+            .with_child((item_a(), DraggedItem(item_c(), UVec2::ZERO), RotatingMarker(false)))
             .with_child(item_b())
             .with_child(item_c())
             .with_child(item_d());