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query.rs
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query.rs
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use crate::{
component::Component,
entity::Entity,
query::{
QueryCombinationIter, QueryEntityError, QueryItem, QueryIter, QueryManyIter,
QuerySingleError, QueryState, ROQueryItem, ReadOnlyWorldQuery, WorldQuery,
},
world::{Mut, World},
};
use std::{any::TypeId, borrow::Borrow, fmt::Debug};
/// [System parameter] that provides selective access to the [`Component`] data stored in a [`World`].
///
/// Enables access to [entity identifiers] and [components] from a system, without the need to directly access the world.
/// Its iterators and getter methods return *query items*.
/// Each query item is a type containing data relative to an entity.
///
/// `Query` is a generic data structure that accepts two type parameters, both of which must implement the [`WorldQuery`] trait:
///
/// - **`Q` (query fetch).**
/// The type of data contained in the query item.
/// Only entities that match the requested data will generate an item.
/// - **`F` (query filter).**
/// A set of conditions that determines whether query items should be kept or discarded.
/// This type parameter is optional.
///
/// # System parameter declaration
///
/// A query should always be declared as a system parameter.
/// This section shows the most common idioms involving the declaration of `Query`, emerging by combining [`WorldQuery`] implementors.
///
/// ## Component access
///
/// A query defined with a reference to a component as the query fetch type parameter can be used to generate items that refer to the data of said component.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// # fn immutable_ref(
/// // A component can be accessed by shared reference...
/// query: Query<&ComponentA>
/// # ) {}
/// # bevy_ecs::system::assert_is_system(immutable_ref);
///
/// # fn mutable_ref(
/// // ... or by mutable reference.
/// query: Query<&mut ComponentA>
/// # ) {}
/// # bevy_ecs::system::assert_is_system(mutable_ref);
/// ```
///
/// ## Query filtering
///
/// Setting the query filter type parameter will ensure that each query item satisfies the given condition.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// # #[derive(Component)]
/// # struct ComponentB;
/// # fn system(
/// // Just `ComponentA` data will be accessed, but only for entities that also contain
/// // `ComponentB`.
/// query: Query<&ComponentA, With<ComponentB>>
/// # ) {}
/// # bevy_ecs::system::assert_is_system(system);
/// ```
///
/// ## `WorldQuery` tuples
///
/// Using tuples, each `Query` type parameter can contain multiple elements.
///
/// In the following example, two components are accessed simultaneously, and the query items are filtered on two conditions.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// # #[derive(Component)]
/// # struct ComponentB;
/// # #[derive(Component)]
/// # struct ComponentC;
/// # #[derive(Component)]
/// # struct ComponentD;
/// # fn immutable_ref(
/// query: Query<(&ComponentA, &ComponentB), (With<ComponentC>, Without<ComponentD>)>
/// # ) {}
/// # bevy_ecs::system::assert_is_system(immutable_ref);
/// ```
///
/// ## Entity identifier access
///
/// The identifier of an entity can be made available inside the query item by including [`Entity`] in the query fetch type parameter.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// # fn system(
/// query: Query<(Entity, &ComponentA)>
/// # ) {}
/// # bevy_ecs::system::assert_is_system(system);
/// ```
///
/// ## Optional component access
///
/// A component can be made optional in a query by wrapping it into an [`Option`].
/// In this way, a query item can still be generated even if the queried entity does not contain the wrapped component.
/// In this case, its corresponding value will be `None`.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// # #[derive(Component)]
/// # struct ComponentB;
/// # fn system(
/// // Generates items for entities that contain `ComponentA`, and optionally `ComponentB`.
/// query: Query<(&ComponentA, Option<&ComponentB>)>
/// # ) {}
/// # bevy_ecs::system::assert_is_system(system);
/// ```
///
/// See the documentation for [`AnyOf`] to idiomatically declare many optional components.
///
/// See the [performance] section to learn more about the impact of optional components.
///
/// ## Disjoint queries
///
/// A system cannot contain two queries that break Rust's mutability rules.
/// In this case, the [`Without`] filter can be used to disjoint them.
///
/// In the following example, two queries mutably access the same component.
/// Executing this system will panic, since an entity could potentially match the two queries at the same time by having both `Player` and `Enemy` components.
/// This would violate mutability rules.
///
/// ```should_panic
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct Health;
/// # #[derive(Component)]
/// # struct Player;
/// # #[derive(Component)]
/// # struct Enemy;
/// #
/// fn randomize_health(
/// player_query: Query<&mut Health, With<Player>>,
/// enemy_query: Query<&mut Health, With<Enemy>>,
/// )
/// # {}
/// # let mut randomize_health_system = bevy_ecs::system::IntoSystem::into_system(randomize_health);
/// # let mut world = World::new();
/// # randomize_health_system.initialize(&mut world);
/// # randomize_health_system.run((), &mut world);
/// ```
///
/// Adding a `Without` filter will disjoint the queries.
/// In this way, any entity that has both `Player` and `Enemy` components is excluded from both queries.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct Health;
/// # #[derive(Component)]
/// # struct Player;
/// # #[derive(Component)]
/// # struct Enemy;
/// #
/// fn randomize_health(
/// player_query: Query<&mut Health, (With<Player>, Without<Enemy>)>,
/// enemy_query: Query<&mut Health, (With<Enemy>, Without<Player>)>,
/// )
/// # {}
/// # let mut randomize_health_system = bevy_ecs::system::IntoSystem::into_system(randomize_health);
/// # let mut world = World::new();
/// # randomize_health_system.initialize(&mut world);
/// # randomize_health_system.run((), &mut world);
/// ```
///
/// An alternative to this idiom is to wrap the conflicting queries into a [`ParamSet`](super::ParamSet).
///
/// # Accessing query items
///
/// The following table summarizes the behavior of the safe methods that can be used to get query items.
///
/// |Query methods|Effect|
/// |:---:|---|
/// |[`iter`]\([`_mut`][`iter_mut`])|Returns an iterator over all query items.|
/// |[`for_each`]\([`_mut`][`for_each_mut`]),<br>[`par_for_each`]\([`_mut`][`par_for_each_mut`])|Runs a specified function for each query item.|
/// |[`iter_many`]\([`_mut`][`iter_many_mut`])|Iterates or runs a specified function over query items generated by a list of entities.|
/// |[`iter_combinations`]\([`_mut`][`iter_combinations_mut`])|Returns an iterator over all combinations of a specified number of query items.|
/// |[`get`]\([`_mut`][`get_mut`])|Returns the query item for the specified entity.|
/// |[`many`]\([`_mut`][`many_mut`]),<br>[`get_many`]\([`_mut`][`get_many_mut`])|Returns the query items for the specified entities.|
/// |[`single`]\([`_mut`][`single_mut`]),<br>[`get_single`]\([`_mut`][`get_single_mut`])|Returns the query item while verifying that there aren't others.|
///
/// There are two methods for each type of query operation: immutable and mutable (ending with `_mut`).
/// When using immutable methods, the query items returned are of type [`ROQueryItem`], a read-only version of the query item.
/// In this circumstance, every mutable reference in the query fetch type parameter is substituted by a shared reference.
///
/// # Performance
///
/// Creating a `Query` is a low-cost constant operation.
/// Iterating it, on the other hand, fetches data from the world and generates items, which can have a significant computational cost.
///
/// [`Table`] component storage type is much more optimized for query iteration than [`SparseSet`].
///
/// Two systems cannot be executed in parallel if both access the same component type where at least one of the accesses is mutable.
/// This happens unless the executor can verify that no entity could be found in both queries.
///
/// Optional components increase the number of entities a query has to match against.
/// This can hurt iteration performance, especially if the query solely consists of only optional components, since the query would iterate over each entity in the world.
///
/// The following table compares the computational complexity of the various methods and operations, where:
///
/// - **n** is the number of entities that match the query,
/// - **r** is the number of elements in a combination,
/// - **k** is the number of involved entities in the operation,
/// - **a** is the number of archetypes in the world,
/// - **C** is the [binomial coefficient], used to count combinations.
/// <sub>n</sub>C<sub>r</sub> is read as "*n* choose *r*" and is equivalent to the number of distinct unordered subsets of *r* elements that can be taken from a set of *n* elements.
///
/// |Query operation|Computational complexity|
/// |:---:|:---:|
/// |[`iter`]\([`_mut`][`iter_mut`])|O(n)|
/// |[`for_each`]\([`_mut`][`for_each_mut`]),<br>[`par_for_each`]\([`_mut`][`par_for_each_mut`])|O(n)|
/// |[`iter_many`]\([`_mut`][`iter_many_mut`])|O(k)|
/// |[`iter_combinations`]\([`_mut`][`iter_combinations_mut`])|O(<sub>n</sub>C<sub>r</sub>)|
/// |[`get`]\([`_mut`][`get_mut`])|O(1)|
/// |([`get_`][`get_many`])[`many`]|O(k)|
/// |([`get_`][`get_many_mut`])[`many_mut`]|O(k<sup>2</sup>)|
/// |[`single`]\([`_mut`][`single_mut`]),<br>[`get_single`]\([`_mut`][`get_single_mut`])|O(a)|
/// |Archetype based filtering ([`With`], [`Without`], [`Or`])|O(a)|
/// |Change detection filtering ([`Added`], [`Changed`])|O(a + n)|
///
/// `for_each` methods are seen to be generally faster than their `iter` version on worlds with high archetype fragmentation.
/// As iterators are in general more flexible and better integrated with the rest of the Rust ecosystem,
/// it is advised to use `iter` methods over `for_each`.
/// It is strongly advised to only use `for_each` if it tangibly improves performance:
/// be sure profile or benchmark both before and after the change.
///
/// [`Added`]: crate::query::Added
/// [`AnyOf`]: crate::query::AnyOf
/// [binomial coefficient]: https://en.wikipedia.org/wiki/Binomial_coefficient
/// [`Changed`]: crate::query::Changed
/// [components]: crate::component::Component
/// [entity identifiers]: crate::entity::Entity
/// [`for_each`]: Self::for_each
/// [`for_each_mut`]: Self::for_each_mut
/// [`get`]: Self::get
/// [`get_many`]: Self::get_many
/// [`get_many_mut`]: Self::get_many_mut
/// [`get_mut`]: Self::get_mut
/// [`get_single`]: Self::get_single
/// [`get_single_mut`]: Self::get_single_mut
/// [`iter`]: Self::iter
/// [`iter_combinations`]: Self::iter_combinations
/// [`iter_combinations_mut`]: Self::iter_combinations_mut
/// [`iter_many`]: Self::iter_many
/// [`iter_many_mut`]: Self::iter_many_mut
/// [`iter_mut`]: Self::iter_mut
/// [`many`]: Self::many
/// [`many_mut`]: Self::many_mut
/// [`Or`]: crate::query::Or
/// [`par_for_each`]: Self::par_for_each
/// [`par_for_each_mut`]: Self::par_for_each_mut
/// [performance]: #performance
/// [`single`]: Self::single
/// [`single_mut`]: Self::single_mut
/// [`SparseSet`]: crate::storage::SparseSet
/// [System parameter]: crate::system::SystemParam
/// [`Table`]: crate::storage::Table
/// [`With`]: crate::query::With
/// [`Without`]: crate::query::Without
pub struct Query<'world, 'state, Q: WorldQuery, F: ReadOnlyWorldQuery = ()> {
pub(crate) world: &'world World,
pub(crate) state: &'state QueryState<Q, F>,
pub(crate) last_change_tick: u32,
pub(crate) change_tick: u32,
}
impl<'w, 's, Q: WorldQuery, F: ReadOnlyWorldQuery> Query<'w, 's, Q, F> {
/// Creates a new query.
///
/// # Safety
///
/// This will create a query that could violate memory safety rules. Make sure that this is only
/// called in ways that ensure the queries have unique mutable access.
#[inline]
pub(crate) unsafe fn new(
world: &'w World,
state: &'s QueryState<Q, F>,
last_change_tick: u32,
change_tick: u32,
) -> Self {
Self {
world,
state,
last_change_tick,
change_tick,
}
}
/// Returns another `Query` from this that fetches the read-only version of the query items.
///
/// For example, `Query<(&mut A, &B, &mut C), With<D>>` will become `Query<(&A, &B, &C), With<D>>`.
/// This can be useful when working around the borrow checker,
/// or reusing functionality between systems via functions that accept query types.
pub fn to_readonly(&self) -> Query<'_, 's, Q::ReadOnly, F::ReadOnly> {
let new_state = self.state.as_readonly();
// SAFETY: This is memory safe because it turns the query immutable.
unsafe {
Query::new(
self.world,
new_state,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns an [`Iterator`] over the read-only query items.
///
/// # Example
///
/// Here, the `report_names_system` iterates over the `Player` component of every entity that contains it:
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Component)]
/// # struct Player { name: String }
/// #
/// fn report_names_system(query: Query<&Player>) {
/// for player in &query {
/// println!("Say hello to {}!", player.name);
/// }
/// }
/// # bevy_ecs::system::assert_is_system(report_names_system);
/// ```
///
/// # See also
///
/// - [`iter_mut`](Self::iter_mut) for mutable query items.
/// - [`for_each`](Self::for_each) for the closure based alternative.
#[inline]
pub fn iter(&self) -> QueryIter<'_, 's, Q::ReadOnly, F::ReadOnly> {
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.as_readonly().iter_unchecked_manual(
self.world,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns an [`Iterator`] over the query items.
///
/// # Example
///
/// Here, the `gravity_system` updates the `Velocity` component of every entity that contains it:
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Component)]
/// # struct Velocity { x: f32, y: f32, z: f32 }
/// fn gravity_system(mut query: Query<&mut Velocity>) {
/// const DELTA: f32 = 1.0 / 60.0;
/// for mut velocity in &mut query {
/// velocity.y -= 9.8 * DELTA;
/// }
/// }
/// # bevy_ecs::system::assert_is_system(gravity_system);
/// ```
///
/// # See also
///
/// - [`iter`](Self::iter) for read-only query items.
/// - [`for_each_mut`](Self::for_each_mut) for the closure based alternative.
#[inline]
pub fn iter_mut(&mut self) -> QueryIter<'_, 's, Q, F> {
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state
.iter_unchecked_manual(self.world, self.last_change_tick, self.change_tick)
}
}
/// Returns a [`QueryCombinationIter`] over all combinations of `K` read-only query items without repetition.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// #
/// fn some_system(query: Query<&ComponentA>) {
/// for [a1, a2] in query.iter_combinations() {
/// // ...
/// }
/// }
/// ```
///
/// # See also
///
/// - [`iter_combinations_mut`](Self::iter_combinations_mut) for mutable query item combinations.
#[inline]
pub fn iter_combinations<const K: usize>(
&self,
) -> QueryCombinationIter<'_, 's, Q::ReadOnly, F::ReadOnly, K> {
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.as_readonly().iter_combinations_unchecked_manual(
self.world,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns a [`QueryCombinationIter`] over all combinations of `K` query items without repetition.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct ComponentA;
/// fn some_system(mut query: Query<&mut ComponentA>) {
/// let mut combinations = query.iter_combinations_mut();
/// while let Some([mut a1, mut a2]) = combinations.fetch_next() {
/// // mutably access components data
/// }
/// }
/// ```
///
/// # See also
///
/// - [`iter_combinations`](Self::iter_combinations) for read-only query item combinations.
#[inline]
pub fn iter_combinations_mut<const K: usize>(
&mut self,
) -> QueryCombinationIter<'_, 's, Q, F, K> {
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.iter_combinations_unchecked_manual(
self.world,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns an [`Iterator`] over the read-only query items generated from an [`Entity`] list.
///
/// # Example
///
/// ```
/// # use bevy_ecs::prelude::*;
/// # #[derive(Component)]
/// # struct Counter {
/// # value: i32
/// # }
/// #
/// // A component containing an entity list.
/// #[derive(Component)]
/// struct Friends {
/// list: Vec<Entity>,
/// }
///
/// fn system(
/// friends_query: Query<&Friends>,
/// counter_query: Query<&Counter>,
/// ) {
/// for friends in &friends_query {
/// for counter in counter_query.iter_many(&friends.list) {
/// println!("Friend's counter: {:?}", counter.value);
/// }
/// }
/// }
/// # bevy_ecs::system::assert_is_system(system);
/// ```
///
/// # See also
///
/// - [`iter_many_mut`](Self::iter_many_mut) to get mutable query items.
#[inline]
pub fn iter_many<EntityList: IntoIterator>(
&self,
entities: EntityList,
) -> QueryManyIter<'_, 's, Q::ReadOnly, F::ReadOnly, EntityList::IntoIter>
where
EntityList::Item: Borrow<Entity>,
{
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.as_readonly().iter_many_unchecked_manual(
entities,
self.world,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns an [`Iterator`] over the query items generated from an [`Entity`] list.
///
/// # Examples
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #[derive(Component)]
/// struct Counter {
/// value: i32
/// }
///
/// #[derive(Component)]
/// struct Friends {
/// list: Vec<Entity>,
/// }
///
/// fn system(
/// friends_query: Query<&Friends>,
/// mut counter_query: Query<&mut Counter>,
/// ) {
/// for friends in &friends_query {
/// let mut iter = counter_query.iter_many_mut(&friends.list);
/// while let Some(mut counter) = iter.fetch_next() {
/// println!("Friend's counter: {:?}", counter.value);
/// counter.value += 1;
/// }
/// }
/// }
/// # bevy_ecs::system::assert_is_system(system);
/// ```
#[inline]
pub fn iter_many_mut<EntityList: IntoIterator>(
&mut self,
entities: EntityList,
) -> QueryManyIter<'_, 's, Q, F, EntityList::IntoIter>
where
EntityList::Item: Borrow<Entity>,
{
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.iter_many_unchecked_manual(
entities,
self.world,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns an [`Iterator`] over the query items.
///
/// # Safety
///
/// This function makes it possible to violate Rust's aliasing guarantees.
/// You must make sure this call does not result in multiple mutable references to the same component.
///
/// # See also
///
/// - [`iter`](Self::iter) and [`iter_mut`](Self::iter_mut) for the safe versions.
#[inline]
pub unsafe fn iter_unsafe(&self) -> QueryIter<'_, 's, Q, F> {
// SEMI-SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
self.state
.iter_unchecked_manual(self.world, self.last_change_tick, self.change_tick)
}
/// Iterates over all possible combinations of `K` query items without repetition.
///
/// # Safety
///
/// This allows aliased mutability.
/// You must make sure this call does not result in multiple mutable references to the same component.
///
/// # See also
///
/// - [`iter_combinations`](Self::iter_combinations) and [`iter_combinations_mut`](Self::iter_combinations_mut) for the safe versions.
#[inline]
pub unsafe fn iter_combinations_unsafe<const K: usize>(
&self,
) -> QueryCombinationIter<'_, 's, Q, F, K> {
// SEMI-SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
self.state.iter_combinations_unchecked_manual(
self.world,
self.last_change_tick,
self.change_tick,
)
}
/// Returns an [`Iterator`] over the query items generated from an [`Entity`] list.
///
/// # Safety
///
/// This allows aliased mutability and does not check for entity uniqueness.
/// You must make sure this call does not result in multiple mutable references to the same component.
/// Particular care must be taken when collecting the data (rather than iterating over it one item at a time) such as via [`Iterator::collect`].
///
/// # See also
///
/// - [`iter_many_mut`](Self::iter_many_mut) to safely access the query items.
pub unsafe fn iter_many_unsafe<EntityList: IntoIterator>(
&self,
entities: EntityList,
) -> QueryManyIter<'_, 's, Q, F, EntityList::IntoIter>
where
EntityList::Item: Borrow<Entity>,
{
self.state.iter_many_unchecked_manual(
entities,
self.world,
self.last_change_tick,
self.change_tick,
)
}
/// Runs `f` on each read-only query item.
///
/// # Example
///
/// Here, the `report_names_system` iterates over the `Player` component of every entity that contains it:
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Component)]
/// # struct Player { name: String }
/// #
/// fn report_names_system(query: Query<&Player>) {
/// query.for_each(|player| {
/// println!("Say hello to {}!", player.name);
/// });
/// }
/// # bevy_ecs::system::assert_is_system(report_names_system);
/// ```
///
/// # See also
///
/// - [`for_each_mut`](Self::for_each_mut) to operate on mutable query items.
/// - [`iter`](Self::iter) for the iterator based alternative.
#[inline]
pub fn for_each<'this>(&'this self, f: impl FnMut(ROQueryItem<'this, Q>)) {
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.as_readonly().for_each_unchecked_manual(
self.world,
f,
self.last_change_tick,
self.change_tick,
);
};
}
/// Runs `f` on each query item.
///
/// # Example
///
/// Here, the `gravity_system` updates the `Velocity` component of every entity that contains it:
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Component)]
/// # struct Velocity { x: f32, y: f32, z: f32 }
/// fn gravity_system(mut query: Query<&mut Velocity>) {
/// const DELTA: f32 = 1.0 / 60.0;
/// query.for_each_mut(|mut velocity| {
/// velocity.y -= 9.8 * DELTA;
/// });
/// }
/// # bevy_ecs::system::assert_is_system(gravity_system);
/// ```
///
/// # See also
///
/// - [`for_each`](Self::for_each) to operate on read-only query items.
/// - [`iter_mut`](Self::iter_mut) for the iterator based alternative.
#[inline]
pub fn for_each_mut<'a>(&'a mut self, f: impl FnMut(QueryItem<'a, Q>)) {
// SAFETY: system runs without conflicts with other systems. same-system queries have runtime
// borrow checks when they conflict
unsafe {
self.state.for_each_unchecked_manual(
self.world,
f,
self.last_change_tick,
self.change_tick,
);
};
}
/// Runs `f` on each read-only query item in parallel.
///
/// Parallelization is achieved by using the [`World`]'s [`ComputeTaskPool`].
///
/// # Tasks and batch size
///
/// The items in the query get sorted into batches.
/// Internally, this function spawns a group of futures that each take on a `batch_size` sized section of the items (or less if the division is not perfect).
/// Then, the tasks in the [`ComputeTaskPool`] work through these futures.
///
/// You can use this value to tune between maximum multithreading ability (many small batches) and minimum parallelization overhead (few big batches).
/// Rule of thumb: If the function body is (mostly) computationally expensive but there are not many items, a small batch size (=more batches) may help to even out the load.
/// If the body is computationally cheap and you have many items, a large batch size (=fewer batches) avoids spawning additional futures that don't help to even out the load.
///
/// [`ComputeTaskPool`]: bevy_tasks::prelude::ComputeTaskPool
///
/// # Panics
///
/// This method panics if the [`ComputeTaskPool`] resource is added to the `World` before using this method.
/// If using this from a query that is being initialized and run from the [`Schedule`](crate::schedule::Schedule), this never panics.
///
/// # See also
///
/// - [`par_for_each_mut`](Self::par_for_each_mut) for operating on mutable query items.
#[inline]
pub fn par_for_each<'this>(
&'this self,
batch_size: usize,
f: impl Fn(ROQueryItem<'this, Q>) + Send + Sync + Clone,
) {
// SAFETY: system runs without conflicts with other systems. same-system queries have runtime
// borrow checks when they conflict
unsafe {
self.state.as_readonly().par_for_each_unchecked_manual(
self.world,
batch_size,
f,
self.last_change_tick,
self.change_tick,
);
};
}
/// Runs `f` on each read-only query item in parallel.
///
/// Parallelization is achieved by using the [`World`]'s [`ComputeTaskPool`].
///
/// # Panics
///
/// This method panics if the [`ComputeTaskPool`] resource is added to the `World` before using this method.
/// If using this from a query that is being initialized and run from the [`Schedule`](crate::schedule::Schedule), this never panics.
///
/// [`ComputeTaskPool`]: bevy_tasks::prelude::ComputeTaskPool
///
/// # See also
///
/// - [`par_for_each`](Self::par_for_each) for more usage details.
#[inline]
pub fn par_for_each_mut<'a>(
&'a mut self,
batch_size: usize,
f: impl Fn(QueryItem<'a, Q>) + Send + Sync + Clone,
) {
// SAFETY: system runs without conflicts with other systems. same-system queries have runtime
// borrow checks when they conflict
unsafe {
self.state.par_for_each_unchecked_manual(
self.world,
batch_size,
f,
self.last_change_tick,
self.change_tick,
);
};
}
/// Returns the read-only query item for the given [`Entity`].
///
/// In case of a nonexisting entity or mismatched component, a [`QueryEntityError`] is returned instead.
///
/// # Example
///
/// Here, `get` is used to retrieve the exact query item of the entity specified by the `SelectedCharacter` resource.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Resource)]
/// # struct SelectedCharacter { entity: Entity }
/// # #[derive(Component)]
/// # struct Character { name: String }
/// #
/// fn print_selected_character_name_system(
/// query: Query<&Character>,
/// selection: Res<SelectedCharacter>
/// )
/// {
/// if let Ok(selected_character) = query.get(selection.entity) {
/// println!("{}", selected_character.name);
/// }
/// }
/// # bevy_ecs::system::assert_is_system(print_selected_character_name_system);
/// ```
///
/// # See also
///
/// - [`get_mut`](Self::get_mut) to get a mutable query item.
#[inline]
pub fn get(&self, entity: Entity) -> Result<ROQueryItem<'_, Q>, QueryEntityError> {
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.as_readonly().get_unchecked_manual(
self.world,
entity,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns the read-only query items for the given array of [`Entity`].
///
/// In case of a nonexisting entity or mismatched component, a [`QueryEntityError`] is returned instead.
/// The elements of the array do not need to be unique, unlike `get_many_mut`.
///
/// # See also
///
/// - [`get_many_mut`](Self::get_many_mut) to get mutable query items.
/// - [`many`](Self::many) for the panicking version.
#[inline]
pub fn get_many<const N: usize>(
&self,
entities: [Entity; N],
) -> Result<[ROQueryItem<'_, Q>; N], QueryEntityError> {
// SAFETY: it is the scheduler's responsibility to ensure that `Query` is never handed out on the wrong `World`.
unsafe {
self.state.get_many_read_only_manual(
self.world,
entities,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns the read-only query items for the given array of [`Entity`].
///
/// # Panics
///
/// This method panics if there is a query mismatch or a non-existing entity.
///
/// # Examples
/// ```rust, no_run
/// use bevy_ecs::prelude::*;
///
/// #[derive(Component)]
/// struct Targets([Entity; 3]);
///
/// #[derive(Component)]
/// struct Position{
/// x: i8,
/// y: i8
/// };
///
/// impl Position {
/// fn distance(&self, other: &Position) -> i8 {
/// // Manhattan distance is way easier to compute!
/// (self.x - other.x).abs() + (self.y - other.y).abs()
/// }
/// }
///
/// fn check_all_targets_in_range(targeting_query: Query<(Entity, &Targets, &Position)>, targets_query: Query<&Position>){
/// for (targeting_entity, targets, origin) in &targeting_query {
/// // We can use "destructuring" to unpack the results nicely
/// let [target_1, target_2, target_3] = targets_query.many(targets.0);
///
/// assert!(target_1.distance(origin) <= 5);
/// assert!(target_2.distance(origin) <= 5);
/// assert!(target_3.distance(origin) <= 5);
/// }
/// }
/// ```
///
/// # See also
///
/// - [`get_many`](Self::get_many) for the non-panicking version.
#[inline]
pub fn many<const N: usize>(&self, entities: [Entity; N]) -> [ROQueryItem<'_, Q>; N] {
self.get_many(entities).unwrap()
}
/// Returns the query item for the given [`Entity`].
///
/// In case of a nonexisting entity or mismatched component, a [`QueryEntityError`] is returned instead.
///
/// # Example
///
/// Here, `get_mut` is used to retrieve the exact query item of the entity specified by the `PoisonedCharacter` resource.
///
/// ```
/// # use bevy_ecs::prelude::*;
/// #
/// # #[derive(Resource)]
/// # struct PoisonedCharacter { character_id: Entity }
/// # #[derive(Component)]
/// # struct Health(u32);
/// #
/// fn poison_system(mut query: Query<&mut Health>, poisoned: Res<PoisonedCharacter>) {
/// if let Ok(mut health) = query.get_mut(poisoned.character_id) {
/// health.0 -= 1;
/// }
/// }
/// # bevy_ecs::system::assert_is_system(poison_system);
/// ```
///
/// # See also
///
/// - [`get`](Self::get) to get a read-only query item.
#[inline]
pub fn get_mut(&mut self, entity: Entity) -> Result<QueryItem<'_, Q>, QueryEntityError> {
// SAFETY: system runs without conflicts with other systems.
// same-system queries have runtime borrow checks when they conflict
unsafe {
self.state.get_unchecked_manual(
self.world,
entity,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns the query items for the given array of [`Entity`].
///
/// In case of a nonexisting entity, duplicate entities or mismatched component, a [`QueryEntityError`] is returned instead.
///
/// # See also
///
/// - [`get_many`](Self::get_many) to get read-only query items.
/// - [`many_mut`](Self::many_mut) for the panicking version.
#[inline]
pub fn get_many_mut<const N: usize>(
&mut self,
entities: [Entity; N],
) -> Result<[QueryItem<'_, Q>; N], QueryEntityError> {
// SAFETY: scheduler ensures safe Query world access
unsafe {
self.state.get_many_unchecked_manual(
self.world,
entities,
self.last_change_tick,
self.change_tick,
)
}
}
/// Returns the query items for the given array of [`Entity`].
///
/// # Panics
///
/// This method panics if there is a query mismatch, a non-existing entity, or the same `Entity` is included more than once in the array.
///
/// # Examples
///
/// ```rust, no_run
/// use bevy_ecs::prelude::*;
///
/// #[derive(Component)]
/// struct Spring{
/// connected_entities: [Entity; 2],
/// strength: f32,
/// }
///
/// #[derive(Component)]
/// struct Position {
/// x: f32,
/// y: f32,
/// }
///
/// #[derive(Component)]
/// struct Force {
/// x: f32,
/// y: f32,
/// }
///
/// fn spring_forces(spring_query: Query<&Spring>, mut mass_query: Query<(&Position, &mut Force)>){
/// for spring in &spring_query {
/// // We can use "destructuring" to unpack our query items nicely
/// let [(position_1, mut force_1), (position_2, mut force_2)] = mass_query.many_mut(spring.connected_entities);
///
/// force_1.x += spring.strength * (position_1.x - position_2.x);
/// force_1.y += spring.strength * (position_1.y - position_2.y);