Function check_visibility 

pub fn check_visibility(
    thread_queues: Local<'_, Parallel<HashMap<TypeId, Vec<Entity>, NoOpHash>>>,
    view_query: Query<'_, '_, (Entity, &mut VisibleEntities, &Frustum, Option<&RenderLayers>, &Camera, Has<NoCpuCulling>)>,
    visible_aabb_query: Query<'_, '_, (Entity, &InheritedVisibility, &mut ViewVisibility, &VisibilityClass, Option<&RenderLayers>, Option<&Aabb>, &GlobalTransform, Has<NoFrustumCulling>, Has<VisibilityRange>)>,
    visible_entity_ranges: Option<Res<'_, VisibleEntityRanges>>,
    previous_visible_entities: ResMut<'_, PreviousVisibleEntities>,
)

System updating the visibility of entities each frame.

The system is part of the VisibilitySystems::CheckVisibility set. Each frame, it updates the ViewVisibility of all entities, and for each view also compute the VisibleEntities for that view.

To ensure that an entity is checked for visibility, make sure that it has a VisibilityClass component and that that component is nonempty.