1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270
//! Alerting events when a component is removed from an entity.
use crate::{
self as bevy_ecs,
component::{Component, ComponentId, ComponentIdFor, Tick},
entity::Entity,
event::{Event, EventId, EventIterator, EventIteratorWithId, Events, ManualEventReader},
prelude::Local,
storage::SparseSet,
system::{ReadOnlySystemParam, SystemMeta, SystemParam},
world::{unsafe_world_cell::UnsafeWorldCell, World},
};
use std::{
fmt::Debug,
iter,
marker::PhantomData,
ops::{Deref, DerefMut},
option,
};
/// Wrapper around [`Entity`] for [`RemovedComponents`].
/// Internally, `RemovedComponents` uses these as an `Events<RemovedComponentEntity>`.
#[derive(Event, Debug, Clone)]
pub struct RemovedComponentEntity(Entity);
impl From<RemovedComponentEntity> for Entity {
fn from(value: RemovedComponentEntity) -> Self {
value.0
}
}
/// Wrapper around a [`ManualEventReader<RemovedComponentEntity>`] so that we
/// can differentiate events between components.
#[derive(Debug)]
pub struct RemovedComponentReader<T>
where
T: Component,
{
reader: ManualEventReader<RemovedComponentEntity>,
marker: PhantomData<T>,
}
impl<T: Component> Default for RemovedComponentReader<T> {
fn default() -> Self {
Self {
reader: Default::default(),
marker: PhantomData,
}
}
}
impl<T: Component> Deref for RemovedComponentReader<T> {
type Target = ManualEventReader<RemovedComponentEntity>;
fn deref(&self) -> &Self::Target {
&self.reader
}
}
impl<T: Component> DerefMut for RemovedComponentReader<T> {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.reader
}
}
/// Stores the [`RemovedComponents`] event buffers for all types of component in a given [`World`].
#[derive(Default, Debug)]
pub struct RemovedComponentEvents {
event_sets: SparseSet<ComponentId, Events<RemovedComponentEntity>>,
}
impl RemovedComponentEvents {
/// Creates an empty storage buffer for component removal events.
pub fn new() -> Self {
Self::default()
}
/// For each type of component, swaps the event buffers and clears the oldest event buffer.
/// In general, this should be called once per frame/update.
pub fn update(&mut self) {
for (_component_id, events) in self.event_sets.iter_mut() {
events.update();
}
}
/// Returns an iterator over components and their entity events.
pub fn iter(&self) -> impl Iterator<Item = (&ComponentId, &Events<RemovedComponentEntity>)> {
self.event_sets.iter()
}
/// Gets the event storage for a given component.
pub fn get(
&self,
component_id: impl Into<ComponentId>,
) -> Option<&Events<RemovedComponentEntity>> {
self.event_sets.get(component_id.into())
}
/// Sends a removal event for the specified component.
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(RemovedComponentEntity(entity));
}
}
/// A [`SystemParam`] that yields entities that had their `T` [`Component`]
/// removed or have been despawned with it.
///
/// This acts effectively the same as an [`EventReader`](crate::event::EventReader).
///
/// 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`](World::clear_trackers).
///
/// For users of `bevy` and `bevy_app`, [`World::clear_trackers`](World::clear_trackers) is
/// automatically called by `bevy_app::App::update` and `bevy_app::SubApp::update`.
/// For the main world, this is delayed until after all `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.read().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: ComponentIdFor<'s, T>,
reader: Local<'s, RemovedComponentReader<T>>,
event_sets: &'w RemovedComponentEvents,
}
/// Iterator over entities that had a specific component removed.
///
/// See [`RemovedComponents`].
pub type RemovedIter<'a> = iter::Map<
iter::Flatten<option::IntoIter<iter::Cloned<EventIterator<'a, RemovedComponentEntity>>>>,
fn(RemovedComponentEntity) -> Entity,
>;
/// Iterator over entities that had a specific component removed.
///
/// See [`RemovedComponents`].
pub type RemovedIterWithId<'a> = iter::Map<
iter::Flatten<option::IntoIter<EventIteratorWithId<'a, RemovedComponentEntity>>>,
fn(
(&RemovedComponentEntity, EventId<RemovedComponentEntity>),
) -> (Entity, EventId<RemovedComponentEntity>),
>;
fn map_id_events(
(entity, id): (&RemovedComponentEntity, EventId<RemovedComponentEntity>),
) -> (Entity, EventId<RemovedComponentEntity>) {
(entity.clone().into(), id)
}
// For all practical purposes, the api surface of `RemovedComponents<T>`
// should be similar to `EventReader<T>` to reduce confusion.
impl<'w, 's, T: Component> RemovedComponents<'w, 's, T> {
/// Fetch underlying [`ManualEventReader`].
pub fn reader(&self) -> &ManualEventReader<RemovedComponentEntity> {
&self.reader
}
/// Fetch underlying [`ManualEventReader`] mutably.
pub fn reader_mut(&mut self) -> &mut ManualEventReader<RemovedComponentEntity> {
&mut self.reader
}
/// Fetch underlying [`Events`].
pub fn events(&self) -> Option<&Events<RemovedComponentEntity>> {
self.event_sets.get(self.component_id.get())
}
/// Destructures to get a mutable reference to the `ManualEventReader`
/// and a reference to `Events`.
///
/// This is necessary since Rust can't detect destructuring through methods and most
/// usecases of the reader uses the `Events` as well.
pub fn reader_mut_with_events(
&mut self,
) -> Option<(
&mut RemovedComponentReader<T>,
&Events<RemovedComponentEntity>,
)> {
self.event_sets
.get(self.component_id.get())
.map(|events| (&mut *self.reader, events))
}
/// Iterates over the events this [`RemovedComponents`] has not seen yet. This updates the
/// [`RemovedComponents`]'s event counter, which means subsequent event reads will not include events
/// that happened before now.
pub fn read(&mut self) -> RemovedIter<'_> {
self.reader_mut_with_events()
.map(|(reader, events)| reader.read(events).cloned())
.into_iter()
.flatten()
.map(RemovedComponentEntity::into)
}
/// Like [`read`](Self::read), except also returning the [`EventId`] of the events.
pub fn read_with_id(&mut self) -> RemovedIterWithId<'_> {
self.reader_mut_with_events()
.map(|(reader, events)| reader.read_with_id(events))
.into_iter()
.flatten()
.map(map_id_events)
}
/// Determines the number of removal events available to be read from this [`RemovedComponents`] without consuming any.
pub fn len(&self) -> usize {
self.events()
.map(|events| self.reader.len(events))
.unwrap_or(0)
}
/// Returns `true` if there are no events available to read.
pub fn is_empty(&self) -> bool {
self.events()
.map(|events| self.reader.is_empty(events))
.unwrap_or(true)
}
/// Consumes all available events.
///
/// This means these events will not appear in calls to [`RemovedComponents::read()`] or
/// [`RemovedComponents::read_with_id()`] and [`RemovedComponents::is_empty()`] will return `true`.
pub fn clear(&mut self) {
if let Some((reader, events)) = self.reader_mut_with_events() {
reader.clear(events);
}
}
}
// SAFETY: Only reads World removed component events
unsafe impl<'a> ReadOnlySystemParam for &'a RemovedComponentEvents {}
// SAFETY: no component value access.
unsafe impl<'a> SystemParam for &'a RemovedComponentEvents {
type State = ();
type Item<'w, 's> = &'w RemovedComponentEvents;
fn init_state(_world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {}
#[inline]
unsafe fn get_param<'w, 's>(
_state: &'s mut Self::State,
_system_meta: &SystemMeta,
world: UnsafeWorldCell<'w>,
_change_tick: Tick,
) -> Self::Item<'w, 's> {
world.removed_components()
}
}