Questions on de-spawning and remove functions from Schematics and ProtoCommands/ProtoEntityCommands

[hafiidz]

It is not exactly a stopping issue, so I am asking it here under discussions>Q&A. Need some help to clarify optimum method to despawn, which is related to a previously closed issue (#43).

bevy_proto/examples/custom_schematic.rs

Line 85 in 37a72d7

// It's important we handle any necessary cleanup when removing a schematic.

In the line 85 as per excerpt above, it is noted that we need to define a dedicated way to de-spawn & remove the entity.
I am currently using the method outlined in #43 above. However, in some cases, it doesn't seems to work properly, i.e. the entity retains its value across different AppState switches. Do we have to manually call ProtoEntityCommands::remove as well ya? I added dbg!("test") within fn remove but it doesn't seems to be triggered?

I tried to use the following but received an error:

// fn remove in impl Schematic for Cardset

fn remove(_input: &Self::Input, context: &mut SchematicContext) {
        dbg!("test");
        let world = context.world_mut();
        let mut query = world.query_filtered::<Entity, With<Cardset>>();
        let entity_vec = query.iter(world).collect::<Vec<Entity>>();
        for entity in entity_vec {
            world.despawn(entity);
        }

        context.entity_mut().unwrap().remove::<NodeBundle>();
}

// despawn code
         fn despawn(
                mut commands: Commands,
                mut proto_commands: ProtoEntityCommands, //tried adding this line 1
                query: Query<Entity, With<CardsetRoot>,
                mut is_spawned: ResMut<IsCardsetRootSpawned>,
          ) {
              if let Ok(entity) = query.get_single() {
                  proto_commands.remove(PROTO_ID);  //tried adding this line 2
                  commands.entity(entity).despawn_recursive();
                  is_spawned.value = false;
              }
          }


// error
the trait bound `for<'a, 'b, 'c, 'd, 'e, 'f, 'g, 'h> fn(bevy::prelude::Commands<'a, 'b>, bevy_proto::backend::proto::ProtoEntityCommands<'c, 'd, 'e, Prototype, ProtoConfig>, bevy::prelude::Query<'f, 'g, bevy::prelude::Entity, bevy::prelude::With<CardsetRoot>>, bevy::prelude::ResMut<'h, IsCardsetRootSpawned>) {game::card::cardset::despawn}: bevy::prelude::IntoSystem<(), (), _>` is not satisfied

[hafiidz]

Found out that I forget to include one line into the prototype.ron file, which result in the despawn totally missing the call. Wasn't obvious since I was using macros to copy over the codes. LOL. Lessons learnt here.

It is now behaving as expected across different implementation. At the same time, still curious on the best/optimum way to do de-spawning if there is any.

[MrGVSV]

Hi @hafiidz, really sorry for being so late to respond to this (got some life stuff going on lol).

The remove functionality is mainly meant for two scenarios:

1. Removing the effects of a prototype on an entity
2. Undoing world changes outside the scope of the prototype entity

The example is demonstrating scenario 2: the apply method spawned in some camera entities that were not children of the prototype entity and so when we remove that prototype, we want to "undo" that world mutation by despawning those cameras.

If all schematics in your prototype are just components/bundles, with no other special Schematic implementations, then I would just opt for the normal commands.despawn. Otherwise, like in your case, calling remove first is better.

---

That being said, I think ProtoEntityCommands might benefit from despawn and despawn_recursive methods. These could then remove and despawn/recursively despawn the given entity.