Removing PointLightBundle from Entity makes it disappear

[wbpaley]

Probably obvious to non-newbies--tia for your answer & tolerance!

I want objects to glow (be emissive) and shed light on surrounding objects (with a PointLightBundle) as I hover over them, then return to their former state when I stop hovering.

But when I try to remove the PointLightBundle (the very bottom of this code, my hacked standard bevy_mod_picking minimal.rs) the whole object disappears. Why?

//! A minimal example of how to add picking support to your bevy app.

use bevy::prelude::*;
use bevy_mod_picking::debug::hide_pointer_text;
use bevy_mod_picking::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins.set(low_latency_window_plugin()))
        // All you need to do is add the picking plugin, with your backend of choice enabled in the
        // cargo features. By default, the bevy_mod_raycast backend is enabled via the
        // `backend_raycast` feature.
        .add_plugins(DefaultPickingPlugins)
        .add_systems(Startup, setup)

        .add_systems(Update, un_glow)

        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn((
        PbrBundle {
            mesh: meshes.add(Mesh::from(shape::Plane::from_size(5.0))),
            material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
            ..default()
        },
        PickableBundle::default(), // Optional: adds selection, highlighting, and helper components.
    ));
    commands.spawn(PointLightBundle {
        point_light: PointLight {
            intensity: 1500.0,
            shadows_enabled: true,
            ..default()
        },
        transform: Transform::from_xyz(4.0, 8.0, -4.0),
        ..default()
    });
    commands.spawn((Camera3dBundle {
        transform: Transform::from_xyz(3.0, 3.0, 3.0).looking_at(Vec3::ZERO, Vec3::Y),
        ..default()
    },));

    commands.spawn((
        PbrBundle {
            mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
            material: materials.add(StandardMaterial {
                base_color: Color::rgb(0.8, 0.7, 0.2).into(),
                emissive: Color::rgb(0.8, 0.7, 0.2).into(),
                ..default()
            }),
            transform: Transform::from_xyz(0.0, 0.5, 0.0),
            ..default()
        },
    ))

        //  put a light inside the cube
        .insert(PointLightBundle {
            point_light: PointLight {
                intensity: 5000.0,
                shadows_enabled: true,
                color: Color::rgb(0.8, 0.7, 0.2).into(),
                radius: 0.5,
                ..default()
            },
            transform: Transform::from_xyz(0.0, 0.5, 0.0),
            ..default()
        })

        //  send an event to remove the light after we hover & leave the cube
        .insert((
            PickableBundle::default(),
            On::<Pointer<Out>>::commands_mut(|event, commands| {
                commands.entity(event.target).insert(UnGlow(event.target));
            }),
        ));
}

#[derive(Component)]
pub struct UnGlow(Entity);

pub fn un_glow(
    mut query: Query<(&UnGlow, &mut Transform, &Handle<StandardMaterial>)>,
    mut commands: Commands
) {
    for (un_glow, transform, material_handle) in query.iter_mut() {

        //  expected to just remove the PointLightBundle
        //  instead, this makes the whole object disappear; todo: fix
        commands.entity(un_glow.0).remove::<PointLightBundle>();


        commands.entity(un_glow.0).remove::<UnGlow>();
    }
}

[alice-i-cecile]

By removing the whole bundle, you end up removing the critical SpatialBundle components on your entity, removing its visibility and position. Instead, you want to be more selective in terms of how you stop it from glowing.

[wbpaley]

Thanks! Will hunt for how to be more selective.

[wbpaley]

Didn't need to hunt; my first guess worked. Hope it's correct & idiomatic; do want to do things well here.

For other noobs who might need it to be spelled out, I just removed PointLight instead of PointLightBundle. Do that in the above code and it works.

FWIW, I was expecting PointLight to be inside PointLightBundle, inside the Entity--hierarchical--and I didn't know how to traverse the hierarchy to get to it. Guess Bevy/ECS magic finds it for me; still need to build my own mental model of how...

[wbpaley]

Tried to mark this as answer, too--it was, taught me, and worked.

[rparrett]

Most of the time, PointLightBundle and PbrBundle and other Bundles aren't meant to be inserted onto the same entity. (A notable exception is PickableBundle, which you're using properly.

PointLightBundle and PbrBundle both share a subset of components: Transform, GlobalTransform, Visibility, InheritedVisibility, and ViewVisibility which are required for them to do their things.

When you remove PointLightBundle, you are removing those required components.

It's a bit of a fluke that insert(PointLightBundle) on an existing PbrBundle is doing what you want. This won't be the case for most built-in Bevy bundles. You should spawn a separate PointLightBundle entity as a child of your PbrBundle entity. You can then remove that child in un_glow. Check out the hierarchy example.

[wbpaley]

Lovely; thanks!

Do prefer understanding to magic...