416a33e613
# Objective One of the use-cases for the function `Entity::from_raw` is creating placeholder entity ids, which are meant to be overwritten later. If we use a constant for this instead of `from_raw`, it is more ergonomic and self-documenting. ## Solution Add a constant that returns an entity ID with an index of `u32::MAX` and a generation of zero. Users are instructed to overwrite this value before using it.
56 lines
1.7 KiB
Rust
56 lines
1.7 KiB
Rust
use bevy_ecs::{
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component::Component,
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entity::{Entity, EntityMap, MapEntities, MapEntitiesError},
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reflect::{ReflectComponent, ReflectMapEntities},
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world::{FromWorld, World},
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};
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use bevy_reflect::Reflect;
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use std::ops::Deref;
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/// Holds a reference to the parent entity of this entity.
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/// This component should only be present on entities that actually have a parent entity.
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///
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/// See [`HierarchyQueryExt`] for hierarchy related methods on [`Query`].
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///
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/// [`HierarchyQueryExt`]: crate::query_extension::HierarchyQueryExt
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/// [`Query`]: bevy_ecs::system::Query
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#[derive(Component, Debug, Eq, PartialEq, Reflect)]
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#[reflect(Component, MapEntities, PartialEq)]
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pub struct Parent(pub(crate) Entity);
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impl Parent {
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/// Gets the [`Entity`] ID of the parent.
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pub fn get(&self) -> Entity {
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self.0
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}
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}
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// TODO: We need to impl either FromWorld or Default so Parent can be registered as Reflect.
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// This is because Reflect deserialize by creating an instance and apply a patch on top.
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// However Parent should only ever be set with a real user-defined entity. Its worth looking into
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// better ways to handle cases like this.
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impl FromWorld for Parent {
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fn from_world(_world: &mut World) -> Self {
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Parent(Entity::PLACEHOLDER)
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}
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}
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impl MapEntities for Parent {
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fn map_entities(&mut self, entity_map: &EntityMap) -> Result<(), MapEntitiesError> {
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// Parent of an entity in the new world can be in outside world, in which case it
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// should not be mapped.
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if let Ok(mapped_entity) = entity_map.get(self.0) {
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self.0 = mapped_entity;
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}
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Ok(())
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}
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}
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impl Deref for Parent {
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type Target = Entity;
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fn deref(&self) -> &Self::Target {
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&self.0
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}
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}
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