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# Objective Removal events are unwieldy and require some knowledge of when to put systems that need to catch events for them, it is very easy to end up missing one and end up with memory leak-ish issues where you don't clean up after yourself. ## Solution Consolidate removals with the benefits of `Events<...>` (such as double buffering and per system ticks for reading the events) and reduce the special casing of it, ideally I was hoping to move the removals to a `Resource` in the world, but that seems a bit more rough to implement/maintain because of double mutable borrowing issues. This doesn't go the full length of change detection esque removal detection a la bevyengine/rfcs#44. Just tries to make the current workflow a bit more user friendly so detecting removals isn't such a scheduling nightmare. --- ## Changelog - RemovedComponents<T> is now backed by an `Events<Entity>` for the benefits of double buffering. ## Migration Guide - Add a `mut` for `removed: RemovedComponents<T>` since we are now modifying an event reader internally. - Iterating over removed components now requires `&mut removed_components` or `removed_components.iter()` instead of `&removed_components`.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,169 @@ | ||
| //! Alerting events when a component is removed from an entity. | ||
| use crate::{ | ||
| self as bevy_ecs, | ||
| component::{Component, ComponentId, ComponentIdFor}, | ||
| entity::Entity, | ||
| event::{Events, ManualEventIterator, ManualEventReader}, | ||
| prelude::Local, | ||
| storage::SparseSet, | ||
| system::{ReadOnlySystemParam, SystemMeta, SystemParam}, | ||
| world::World, | ||
| }; | ||
|
|
||
| use std::{ | ||
| fmt::Debug, | ||
| iter, | ||
| marker::PhantomData, | ||
| ops::{Deref, DerefMut}, | ||
| option, | ||
| }; | ||
|
|
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| /// Wrapper around a [`ManualEventReader<Entity>`] so that we | ||
| /// can differentiate events between components. | ||
| #[derive(Debug)] | ||
| pub struct RemovedComponentReader<T> | ||
| where | ||
| T: Component, | ||
| { | ||
| reader: ManualEventReader<Entity>, | ||
| marker: PhantomData<T>, | ||
| } | ||
|
|
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| impl<T: Component> Default for RemovedComponentReader<T> { | ||
| fn default() -> Self { | ||
| Self { | ||
| reader: Default::default(), | ||
| marker: PhantomData, | ||
| } | ||
| } | ||
| } | ||
|
|
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| impl<T: Component> Deref for RemovedComponentReader<T> { | ||
| type Target = ManualEventReader<Entity>; | ||
| fn deref(&self) -> &Self::Target { | ||
| &self.reader | ||
| } | ||
| } | ||
|
|
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| impl<T: Component> DerefMut for RemovedComponentReader<T> { | ||
| fn deref_mut(&mut self) -> &mut Self::Target { | ||
| &mut self.reader | ||
| } | ||
| } | ||
|
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| /// Wrapper around a map of components to [`Events<Entity>`]. | ||
| /// So that we can find the events without naming the type directly. | ||
| #[derive(Default, Debug)] | ||
| pub struct RemovedComponentEvents { | ||
| event_sets: SparseSet<ComponentId, Events<Entity>>, | ||
| } | ||
|
|
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| impl RemovedComponentEvents { | ||
| pub fn new() -> Self { | ||
| Self::default() | ||
| } | ||
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| pub fn update(&mut self) { | ||
| for (_component_id, events) in self.event_sets.iter_mut() { | ||
| events.update(); | ||
| } | ||
| } | ||
|
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| pub fn get(&self, component_id: impl Into<ComponentId>) -> Option<&Events<Entity>> { | ||
| self.event_sets.get(component_id.into()) | ||
| } | ||
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| pub fn send(&mut self, component_id: impl Into<ComponentId>, entity: Entity) { | ||
| self.event_sets | ||
| .get_or_insert_with(component_id.into(), Default::default) | ||
| .send(entity); | ||
| } | ||
| } | ||
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| /// A [`SystemParam`] that grants access to the entities that had their `T` [`Component`] removed. | ||
| /// | ||
| /// Note that this does not allow you to see which data existed before removal. | ||
| /// If you need this, you will need to track the component data value on your own, | ||
| /// using a regularly scheduled system that requests `Query<(Entity, &T), Changed<T>>` | ||
| /// and stores the data somewhere safe to later cross-reference. | ||
| /// | ||
| /// If you are using `bevy_ecs` as a standalone crate, | ||
| /// note that the `RemovedComponents` list will not be automatically cleared for you, | ||
| /// and will need to be manually flushed using [`World::clear_trackers`](crate::world::World::clear_trackers) | ||
| /// | ||
| /// For users of `bevy` and `bevy_app`, this is automatically done in `bevy_app::App::update`. | ||
| /// For the main world, [`World::clear_trackers`](crate::world::World::clear_trackers) is run after the main schedule is run and after | ||
| /// `SubApp`'s have run. | ||
| /// | ||
| /// # Examples | ||
| /// | ||
| /// Basic usage: | ||
| /// | ||
| /// ``` | ||
| /// # use bevy_ecs::component::Component; | ||
| /// # use bevy_ecs::system::IntoSystem; | ||
| /// # use bevy_ecs::removal_detection::RemovedComponents; | ||
| /// # | ||
| /// # #[derive(Component)] | ||
| /// # struct MyComponent; | ||
| /// fn react_on_removal(mut removed: RemovedComponents<MyComponent>) { | ||
| /// removed.iter().for_each(|removed_entity| println!("{:?}", removed_entity)); | ||
| /// } | ||
| /// # bevy_ecs::system::assert_is_system(react_on_removal); | ||
| /// ``` | ||
| #[derive(SystemParam)] | ||
| pub struct RemovedComponents<'w, 's, T: Component> { | ||
| component_id: Local<'s, ComponentIdFor<T>>, | ||
| reader: Local<'s, RemovedComponentReader<T>>, | ||
| event_sets: &'w RemovedComponentEvents, | ||
| } | ||
|
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| /// Iterator over entities that had a specific component removed. | ||
| /// | ||
| /// See [`RemovedComponents`]. | ||
| pub type RemovedIter<'a> = | ||
| iter::Flatten<option::IntoIter<iter::Cloned<ManualEventIterator<'a, Entity>>>>; | ||
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| impl<'w, 's, T: Component> RemovedComponents<'w, 's, T> { | ||
| pub fn iter(&mut self) -> RemovedIter<'_> { | ||
| self.event_sets | ||
| .get(**self.component_id) | ||
| .map(|events| self.reader.iter(events).cloned()) | ||
| .into_iter() | ||
| .flatten() | ||
| } | ||
| } | ||
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| impl<'a, 'w, 's: 'a, T> IntoIterator for &'a mut RemovedComponents<'w, 's, T> | ||
| where | ||
| T: Component, | ||
| { | ||
| type Item = Entity; | ||
| type IntoIter = RemovedIter<'a>; | ||
| fn into_iter(self) -> Self::IntoIter { | ||
| self.iter() | ||
| } | ||
| } | ||
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| // SAFETY: Only reads World removed component events | ||
| unsafe impl<'a> ReadOnlySystemParam for &'a RemovedComponentEvents {} | ||
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| // SAFETY: no component value access, removed component events can be read in parallel and are | ||
| // never mutably borrowed during system execution | ||
| unsafe impl<'a> SystemParam for &'a RemovedComponentEvents { | ||
| type State = (); | ||
| type Item<'w, 's> = &'w RemovedComponentEvents; | ||
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| fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {} | ||
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| #[inline] | ||
| unsafe fn get_param<'w, 's>( | ||
| _state: &'s mut Self::State, | ||
| _system_meta: &SystemMeta, | ||
| world: &'w World, | ||
| _change_tick: u32, | ||
| ) -> Self::Item<'w, 's> { | ||
| world.removed_components() | ||
| } | ||
| } |
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