Struct Query

pub struct Query<'world, 'state, D, F = ()>
where
    D: QueryData,
    F: QueryFilter,
{ /* private fields */ }

A system parameter that provides selective access to the Component data stored in a World.

Queries enable systems to access entity identifiers and components without requiring direct access to the World. Its iterators and getter methods return query items, which are types containing data related to an entity.

Query is a generic data structure that accepts two type parameters:

• D (query data): The type of data fetched by the query, which will be returned as the query item. Only entities that match the requested data will generate an item. Must implement the QueryData trait.
• F (query filter): An optional set of conditions that determine whether query items should be kept or discarded. This defaults to unit, which means no additional filters will be applied. Must implement the QueryFilter trait.

Similar parameters

Query has few sibling SystemParams, which perform additional validation:

• Single - Exactly one matching query item.
• Option<Single> - Zero or one matching query item.
• Populated - At least one matching query item.

These parameters will prevent systems from running if their requirements are not met.

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.

Component access

You can fetch an entity’s component by specifying a reference to that component in the query’s data parameter:

// A component can be accessed by a shared reference...
fn immutable_query(query: Query<&ComponentA>) {
    // ...
}

// ...or by a mutable reference.
fn mutable_query(query: Query<&mut ComponentA>) {
    // ...
}

Note that components need to be behind a reference (& or &mut), or the query will not compile:

// This needs to be `&ComponentA` or `&mut ComponentA` in order to compile.
fn invalid_query(query: Query<ComponentA>) {
    // ...
}

Query filtering

Setting the query filter type parameter will ensure that each query item satisfies the given condition:

// `ComponentA` data will be accessed, but only for entities that also contain `ComponentB`.
fn filtered_query(query: Query<&ComponentA, With<ComponentB>>) {
    // ...
}

Note that the filter is With<ComponentB>, not With<&ComponentB>. Unlike query data, With does require components to be behind a reference.

QueryData or QueryFilter 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:

fn complex_query(
    query: Query<(&mut ComponentA, &ComponentB), (With<ComponentC>, Without<ComponentD>)>
) {
    // ...
}

Note that this currently only works on tuples with 15 or fewer items. You may nest tuples to get around this limit:

fn nested_query(
    query: Query<(&ComponentA, &ComponentB, (&mut ComponentC, &mut ComponentD))>
) {
    // ...
}

Entity identifier access

You can access Entity, the entity identifier, by including it in the query data parameter:

fn entity_id_query(query: Query<(Entity, &ComponentA)>) {
    // ...
}

Be aware that Entity is not a component, so it does not need to be behind a reference.

Optional component access

A component can be made optional by wrapping it into an Option. In the following example, a query item will still be generated even if the queried entity does not contain ComponentB. When this is the case, Option<&ComponentB>’s corresponding value will be None.

// A queried items must contain `ComponentA`. If they also contain `ComponentB`, its value will
// be fetched as well.
fn optional_component_query(query: Query<(&ComponentA, Option<&ComponentB>)>) {
    // ...
}

Optional components can hurt performance in some cases, so please read the performance section to learn more about them. Additionally, if you need to declare several optional components, you may be interested in using AnyOf.

Disjoint queries

A system cannot contain two queries that break Rust’s mutability rules, or else it will panic when initialized. This can often be fixed with the Without filter, which makes the queries disjoint.

In the following example, the two queries can mutably access the same &mut Health component if an entity has both the Player and Enemy components. Bevy will catch this and panic, however, instead of breaking Rust’s mutability rules:

fn randomize_health(
    player_query: Query<&mut Health, With<Player>>,
    enemy_query: Query<&mut Health, With<Enemy>>,
) {
    // ...
}

Adding a Without filter will disjoint the queries. In the following example, any entity that has both the Player and Enemy components will be excluded from both queries:

fn randomize_health(
    player_query: Query<&mut Health, (With<Player>, Without<Enemy>)>,
    enemy_query: Query<&mut Health, (With<Enemy>, Without<Player>)>,
) {
    // ...
}

An alternative solution to this problem would be to wrap the conflicting queries in ParamSet.

Whole Entity Access

EntityRef can be used in a query to gain read-only access to all components of an entity. This is useful when dynamically fetching components instead of baking them into the query type.

fn all_components_query(query: Query<(EntityRef, &ComponentA)>) {
    // ...
}

As EntityRef can read any component on an entity, a query using it will conflict with any mutable component access.

// `EntityRef` provides read access to *all* components on an entity. When combined with
// `&mut ComponentA` in the same query, it creates a conflict because `EntityRef` could read
// `&ComponentA` while `&mut ComponentA` attempts to modify it - violating Rust's borrowing
// rules.
fn invalid_query(query: Query<(EntityRef, &mut ComponentA)>) {
    // ...
}

It is strongly advised to couple EntityRef queries with the use of either With / Without filters or ParamSets. Not only does this improve the performance and parallelization of the system, but it enables systems to gain mutable access to other components:

// The first query only reads entities that have `ComponentA`, while the second query only
// modifies entities that *don't* have `ComponentA`. Because neither query will access the same
// entity, this system does not conflict.
fn disjoint_query(
    query_a: Query<EntityRef, With<ComponentA>>,
    query_b: Query<&mut ComponentB, Without<ComponentA>>,
) {
    // ...
}

The fundamental rule: EntityRef’s ability to read all components means it can never coexist with mutable access. With / Without filters can guarantee this by keeping the queries on completely separate entities.

Accessing query items

The following table summarizes the behavior of safe methods that can be used to get query items:

Query methods	Effect
iter[_mut]	Returns an iterator over all query items.
iter[_mut]().for_each(), par_iter[_mut]	Runs a specified function for each query item.
iter_many[_unique][_mut]	Iterates over query items that match a list of entities.
iter_combinations[_mut]	Iterates over all combinations of query items.
single[_mut]	Returns a single query item if only one exists.
get[_mut]	Returns the query item for a specified entity.
get_many[_unique][_mut]	Returns all query items that match a list of entities.

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.

Two systems cannot be executed in parallel if both access the same component type where at least one of the accesses is mutable. Because of this, it is recommended for queries to only fetch mutable access to components when necessary, since immutable access can be parallelized.

Query filters (With / Without) can improve performance because they narrow the kinds of entities that can be fetched. Systems that access fewer kinds of entities are more likely to be parallelized by the scheduler.

On the other hand, be careful using optional components (Option<&ComponentA>) and EntityRef because they broaden the amount of entities kinds that can be accessed. This is especially true of a query that only fetches optional components or EntityRef, as the query would iterate over all entities in the world.

There are two types of component storage types: Table and SparseSet. Table offers fast iteration speeds, but slower insertion and removal speeds. SparseSet is the opposite: it offers fast component insertion and removal speeds, but slower iteration speeds.

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. _nC_r 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]	O(n)
iter[_mut]().for_each(), par_iter[_mut]	O(n)
iter_many[_mut]	O(k)
iter_combinations[_mut]	O(nCr)
single[_mut]	O(a)
get[_mut]	O(1)
get_many	O(k)
get_many_mut	O(k2)
Archetype-based filtering (With, Without, Or)	O(a)
Change detection filtering (Added, Changed)	O(a + n)

Iterator::for_each

The for_each methods appear to be generally faster than for-loops when run on worlds with high archetype fragmentation, and may enable additional optimizations like autovectorization. It is strongly advised to only use Iterator::for_each if it tangibly improves performance. Always profile or benchmark before and after the change!

fn system(query: Query<&ComponentA>) {
    // This may result in better performance...
    query.iter().for_each(|component| {
        // ...
    });

    // ...than this. Always benchmark to validate the difference!
    for component in query.iter() {
        // ...
    }
}

Implementations

impl<'w, 's, D, F> Query<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

pub fn related<R>(&'w self, entity: Entity) -> Option<Entity>

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w> = &'w R>,

If the given entity contains the R Relationship component, returns the target entity of that relationship.

pub fn relationship_sources<S>( &'w self, entity: Entity, ) -> impl Iterator<Item = Entity> + 'w

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w> = &'w S>,

If the given entity contains the S RelationshipTarget component, returns the source entities stored on that component.

pub fn root_ancestor<R>(&'w self, entity: Entity) -> Entity

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w> = &'w R>,

Recursively walks up the tree defined by the given R Relationship until there are no more related entities, returning the “root entity” of the relationship hierarchy.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn iter_leaves<S>( &'w self, entity: Entity, ) -> impl Iterator<Item = Entity> + 'w

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w> = &'w S>, <<S as RelationshipTarget>::Collection as RelationshipSourceCollection>::SourceIter<'w>: DoubleEndedIterator,

Iterates all “leaf entities” as defined by the RelationshipTarget hierarchy.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn iter_siblings<R>( &'w self, entity: Entity, ) -> impl Iterator<Item = Entity> + 'w

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w> = (Option<&'w R>, Option<&'w <R as Relationship>::RelationshipTarget>)>,

Iterates all sibling entities that also have the R Relationship with the same target entity.

pub fn iter_descendants<S>( &'w self, entity: Entity, ) -> DescendantIter<'w, 's, D, F, S>

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w> = &'w S>,

Iterates all descendant entities as defined by the given entity’s RelationshipTarget and their recursive RelationshipTarget.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

Examples found in repository

examples/3d/update_gltf_scene.rs (line 65)

fn move_scene_entities(
    time: Res<Time>,
    moved_scene: Query<Entity, With<MovedScene>>,
    children: Query<&Children>,
    mut transforms: Query<&mut Transform>,
) {
    for moved_scene_entity in &moved_scene {
        let mut offset = 0.;
        for entity in children.iter_descendants(moved_scene_entity) {
            if let Ok(mut transform) = transforms.get_mut(entity) {
                transform.translation = Vec3::new(
                    offset * ops::sin(time.elapsed_secs()) / 20.,
                    0.,
                    ops::cos(time.elapsed_secs()) / 20.,
                );
                offset += 0.5;
            }
        }
    }
}

examples/testbed/3d.rs (line 289)

    fn pause_animation_frame(
        trigger: Trigger<SceneInstanceReady>,
        children: Query<&Children>,
        mut commands: Commands,
        animation: Res<Animation>,
        mut players: Query<(Entity, &mut AnimationPlayer)>,
    ) {
        for child in children.iter_descendants(trigger.target()) {
            if let Ok((entity, mut player)) = players.get_mut(child) {
                let mut transitions = AnimationTransitions::new();
                transitions
                    .play(&mut player, animation.animation, Duration::ZERO)
                    .seek_to(0.5)
                    .pause();

                commands
                    .entity(entity)
                    .insert(AnimationGraphHandle(animation.graph.clone()))
                    .insert(transitions);
            }
        }
    }

examples/3d/edit_material_on_gltf.rs (line 73)

fn change_material(
    trigger: Trigger<SceneInstanceReady>,
    mut commands: Commands,
    children: Query<&Children>,
    color_override: Query<&ColorOverride>,
    mesh_materials: Query<&MeshMaterial3d<StandardMaterial>>,
    mut asset_materials: ResMut<Assets<StandardMaterial>>,
) {
    // Get the `ColorOverride` of the entity, if it does not have a color override, skip
    let Ok(color_override) = color_override.get(trigger.target()) else {
        return;
    };

    // Iterate over all children recursively
    for descendants in children.iter_descendants(trigger.target()) {
        // Get the material of the descendant
        if let Some(material) = mesh_materials
            .get(descendants)
            .ok()
            .and_then(|id| asset_materials.get_mut(id.id()))
        {
            // Create a copy of the material and override base color
            // If you intend on creating multiple models with the same tint, it
            // is best to cache the handle somewhere, as having multiple materials
            // that are identical is expensive
            let mut new_material = material.clone();
            new_material.base_color = color_override.0;

            // Override `MeshMaterial3d` with new material
            commands
                .entity(descendants)
                .insert(MeshMaterial3d(asset_materials.add(new_material)));
        }
    }
}

examples/animation/animated_mesh.rs (line 78)

fn play_animation_when_ready(
    trigger: Trigger<SceneInstanceReady>,
    mut commands: Commands,
    children: Query<&Children>,
    animations_to_play: Query<&AnimationToPlay>,
    mut players: Query<&mut AnimationPlayer>,
) {
    // The entity we spawned in `setup_mesh_and_animation` is the trigger's target.
    // Start by finding the AnimationToPlay component we added to that entity.
    if let Ok(animation_to_play) = animations_to_play.get(trigger.target()) {
        // The SceneRoot component will have spawned the scene as a hierarchy
        // of entities parented to our entity. Since the asset contained a skinned
        // mesh and animations, it will also have spawned an animation player
        // component. Search our entity's descendants to find the animation player.
        for child in children.iter_descendants(trigger.target()) {
            if let Ok(mut player) = players.get_mut(child) {
                // Tell the animation player to start the animation and keep
                // repeating it.
                //
                // If you want to try stopping and switching animations, see the
                // `animated_mesh_control.rs` example.
                player.play(animation_to_play.index).repeat();

                // Add the animation graph. This only needs to be done once to
                // connect the animation player to the mesh.
                commands
                    .entity(child)
                    .insert(AnimationGraphHandle(animation_to_play.graph_handle.clone()));
            }
        }
    }
}

pub fn iter_descendants_depth_first<S>( &'w self, entity: Entity, ) -> DescendantDepthFirstIter<'w, 's, D, F, S>

where S: RelationshipTarget, <D as QueryData>::ReadOnly: QueryData<Item<'w> = &'w S>, <<S as RelationshipTarget>::Collection as RelationshipSourceCollection>::SourceIter<'w>: DoubleEndedIterator,

Iterates all descendant entities as defined by the given entity’s RelationshipTarget and their recursive RelationshipTarget in depth-first order.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

pub fn iter_ancestors<R>( &'w self, entity: Entity, ) -> AncestorIter<'w, 's, D, F, R>

where R: Relationship, <D as QueryData>::ReadOnly: QueryData<Item<'w> = &'w R>,

Iterates all ancestors of the given entity as defined by the R Relationship.

Warning

For relationship graphs that contain loops, this could loop infinitely. If your relationship is not a tree (like Bevy’s hierarchy), be sure to stop if you encounter a duplicate entity.

Examples found in repository

examples/ecs/relationships.rs (line 168)

    fn check_for_cycles(
        // We want to check every entity for cycles
        query_to_check: Query<Entity, With<Targeting>>,
        // Fetch the names for easier debugging.
        name_query: Query<&Name>,
        // The targeting_query allows us to traverse the relationship graph.
        targeting_query: Query<&Targeting>,
    ) -> Result<(), TargetingCycle> {
        for initial_entity in query_to_check.iter() {
            let mut visited = EntityHashSet::new();
            let mut targeting_name = name_query.get(initial_entity).unwrap().clone();
            println!("Checking for cycles starting at {targeting_name}",);

            // There's all sorts of methods like this; check the `Query` docs for more!
            // This would also be easy to do by just manually checking the `Targeting` component,
            // and calling `query.get(targeted_entity)` on the entity that it targets in a loop.
            for targeting in targeting_query.iter_ancestors(initial_entity) {
                let target_name = name_query.get(targeting).unwrap();
                println!("{targeting_name} is targeting {target_name}",);
                targeting_name = target_name.clone();

                if !visited.insert(targeting) {
                    return Err(TargetingCycle {
                        initial_entity,
                        visited,
                    });
                }
            }
        }

        // If we've checked all the entities and haven't found a cycle, we're good!
        Ok(())
    }

impl<'w, 's, D, F> Query<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

pub fn as_readonly(&self) -> Query<'_, 's, <D as QueryData>::ReadOnly, F>

Returns another Query from this that fetches the read-only version of the query items.

For example, Query<(&mut D1, &D2, &mut D3), With<F>> will become Query<(&D1, &D2, &D3), With<F>>. This can be useful when working around the borrow checker, or reusing functionality between systems via functions that accept query types.

See also

into_readonly for a version that consumes the Query to return one with the full 'world lifetime.

pub fn into_readonly(self) -> Query<'w, 's, <D as QueryData>::ReadOnly, F>

Returns another Query from this that fetches the read-only version of the query items.

For example, Query<(&mut D1, &D2, &mut D3), With<F>> will become Query<(&D1, &D2, &D3), With<F>>. This can be useful when working around the borrow checker, or reusing functionality between systems via functions that accept query types.

See also

as_readonly for a version that borrows the Query instead of consuming it.

pub fn reborrow(&mut self) -> Query<'_, 's, D, F>

Returns a new Query reborrowing the access from this one. The current query will be unusable while the new one exists.

Example

For example this allows to call other methods or other systems that require an owned Query without completely giving up ownership of it.

fn helper_system(query: Query<&ComponentA>) { /* ... */}

fn system(mut query: Query<&ComponentA>) {
    helper_system(query.reborrow());
    // Can still use query here:
    for component in &query {
        // ...
    }
}

pub unsafe fn reborrow_unsafe(&self) -> Query<'_, 's, D, F>

Returns a new Query reborrowing the access from this one. The current query will still be usable while the new one exists, but must not be used in a way that violates aliasing.

Safety

This function makes it possible to violate Rust’s aliasing guarantees. You must make sure this call does not result in a mutable or shared reference to a component with a mutable reference.

See also

• reborrow for the safe versions.

pub fn iter(&self) -> QueryIter<'_, 's, <D as QueryData>::ReadOnly, F>

Returns an Iterator over the read-only query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Example

Here, the report_names_system iterates over the Player component of every entity that contains it:

fn report_names_system(query: Query<&Player>) {
    for player in &query {
        println!("Say hello to {}!", player.name);
    }
}

See also

iter_mut for mutable query items.

Examples found in repository

examples/ecs/system_param.rs (line 31)

    fn count(&mut self) {
        self.count.0 = self.players.iter().len();
    }

examples/app/headless_renderer.rs (line 326)

fn image_copy_extract(mut commands: Commands, image_copiers: Extract<Query<&ImageCopier>>) {
    commands.insert_resource(ImageCopiers(
        image_copiers.iter().cloned().collect::<Vec<ImageCopier>>(),
    ));
}

/// `RenderGraph` label for `ImageCopyDriver`
#[derive(Debug, PartialEq, Eq, Clone, Hash, RenderLabel)]
struct ImageCopy;

/// `RenderGraph` node
#[derive(Default)]
struct ImageCopyDriver;

// Copies image content from render target to buffer
impl render_graph::Node for ImageCopyDriver {
    fn run(
        &self,
        _graph: &mut RenderGraphContext,
        render_context: &mut RenderContext,
        world: &World,
    ) -> Result<(), NodeRunError> {
        let image_copiers = world.get_resource::<ImageCopiers>().unwrap();
        let gpu_images = world
            .get_resource::<RenderAssets<bevy::render::texture::GpuImage>>()
            .unwrap();

        for image_copier in image_copiers.iter() {
            if !image_copier.enabled() {
                continue;
            }

            let src_image = gpu_images.get(&image_copier.src_image).unwrap();

            let mut encoder = render_context
                .render_device()
                .create_command_encoder(&CommandEncoderDescriptor::default());

            let block_dimensions = src_image.texture_format.block_dimensions();
            let block_size = src_image.texture_format.block_copy_size(None).unwrap();

            // Calculating correct size of image row because
            // copy_texture_to_buffer can copy image only by rows aligned wgpu::COPY_BYTES_PER_ROW_ALIGNMENT
            // That's why image in buffer can be little bit wider
            // This should be taken into account at copy from buffer stage
            let padded_bytes_per_row = RenderDevice::align_copy_bytes_per_row(
                (src_image.size.width as usize / block_dimensions.0 as usize) * block_size as usize,
            );

            encoder.copy_texture_to_buffer(
                src_image.texture.as_image_copy(),
                TexelCopyBufferInfo {
                    buffer: &image_copier.buffer,
                    layout: TexelCopyBufferLayout {
                        offset: 0,
                        bytes_per_row: Some(
                            std::num::NonZero::<u32>::new(padded_bytes_per_row as u32)
                                .unwrap()
                                .into(),
                        ),
                        rows_per_image: None,
                    },
                },
                src_image.size,
            );

            let render_queue = world.get_resource::<RenderQueue>().unwrap();
            render_queue.submit(std::iter::once(encoder.finish()));
        }

        Ok(())
    }
}

/// runs in render world after Render stage to send image from buffer via channel (receiver is in main world)
fn receive_image_from_buffer(
    image_copiers: Res<ImageCopiers>,
    render_device: Res<RenderDevice>,
    sender: Res<RenderWorldSender>,
) {
    for image_copier in image_copiers.0.iter() {
        if !image_copier.enabled() {
            continue;
        }

        // Finally time to get our data back from the gpu.
        // First we get a buffer slice which represents a chunk of the buffer (which we
        // can't access yet).
        // We want the whole thing so use unbounded range.
        let buffer_slice = image_copier.buffer.slice(..);

        // Now things get complicated. WebGPU, for safety reasons, only allows either the GPU
        // or CPU to access a buffer's contents at a time. We need to "map" the buffer which means
        // flipping ownership of the buffer over to the CPU and making access legal. We do this
        // with `BufferSlice::map_async`.
        //
        // The problem is that map_async is not an async function so we can't await it. What
        // we need to do instead is pass in a closure that will be executed when the slice is
        // either mapped or the mapping has failed.
        //
        // The problem with this is that we don't have a reliable way to wait in the main
        // code for the buffer to be mapped and even worse, calling get_mapped_range or
        // get_mapped_range_mut prematurely will cause a panic, not return an error.
        //
        // Using channels solves this as awaiting the receiving of a message from
        // the passed closure will force the outside code to wait. It also doesn't hurt
        // if the closure finishes before the outside code catches up as the message is
        // buffered and receiving will just pick that up.
        //
        // It may also be worth noting that although on native, the usage of asynchronous
        // channels is wholly unnecessary, for the sake of portability to Wasm
        // we'll use async channels that work on both native and Wasm.

        let (s, r) = crossbeam_channel::bounded(1);

        // Maps the buffer so it can be read on the cpu
        buffer_slice.map_async(MapMode::Read, move |r| match r {
            // This will execute once the gpu is ready, so after the call to poll()
            Ok(r) => s.send(r).expect("Failed to send map update"),
            Err(err) => panic!("Failed to map buffer {err}"),
        });

        // In order for the mapping to be completed, one of three things must happen.
        // One of those can be calling `Device::poll`. This isn't necessary on the web as devices
        // are polled automatically but natively, we need to make sure this happens manually.
        // `Maintain::Wait` will cause the thread to wait on native but not on WebGpu.

        // This blocks until the gpu is done executing everything
        render_device.poll(Maintain::wait()).panic_on_timeout();

        // This blocks until the buffer is mapped
        r.recv().expect("Failed to receive the map_async message");

        // This could fail on app exit, if Main world clears resources (including receiver) while Render world still renders
        let _ = sender.send(buffer_slice.get_mapped_range().to_vec());

        // We need to make sure all `BufferView`'s are dropped before we do what we're about
        // to do.
        // Unmap so that we can copy to the staging buffer in the next iteration.
        image_copier.buffer.unmap();
    }
}

/// CPU-side image for saving
#[derive(Component, Deref, DerefMut)]
struct ImageToSave(Handle<Image>);

// Takes from channel image content sent from render world and saves it to disk
fn update(
    images_to_save: Query<&ImageToSave>,
    receiver: Res<MainWorldReceiver>,
    mut images: ResMut<Assets<Image>>,
    mut scene_controller: ResMut<SceneController>,
    mut app_exit_writer: EventWriter<AppExit>,
    mut file_number: Local<u32>,
) {
    if let SceneState::Render(n) = scene_controller.state {
        if n < 1 {
            // We don't want to block the main world on this,
            // so we use try_recv which attempts to receive without blocking
            let mut image_data = Vec::new();
            while let Ok(data) = receiver.try_recv() {
                // image generation could be faster than saving to fs,
                // that's why use only last of them
                image_data = data;
            }
            if !image_data.is_empty() {
                for image in images_to_save.iter() {
                    // Fill correct data from channel to image
                    let img_bytes = images.get_mut(image.id()).unwrap();

                    // We need to ensure that this works regardless of the image dimensions
                    // If the image became wider when copying from the texture to the buffer,
                    // then the data is reduced to its original size when copying from the buffer to the image.
                    let row_bytes = img_bytes.width() as usize
                        * img_bytes.texture_descriptor.format.pixel_size();
                    let aligned_row_bytes = RenderDevice::align_copy_bytes_per_row(row_bytes);
                    if row_bytes == aligned_row_bytes {
                        img_bytes.data.as_mut().unwrap().clone_from(&image_data);
                    } else {
                        // shrink data to original image size
                        img_bytes.data = Some(
                            image_data
                                .chunks(aligned_row_bytes)
                                .take(img_bytes.height() as usize)
                                .flat_map(|row| &row[..row_bytes.min(row.len())])
                                .cloned()
                                .collect(),
                        );
                    }

                    // Create RGBA Image Buffer
                    let img = match img_bytes.clone().try_into_dynamic() {
                        Ok(img) => img.to_rgba8(),
                        Err(e) => panic!("Failed to create image buffer {e:?}"),
                    };

                    // Prepare directory for images, test_images in bevy folder is used here for example
                    // You should choose the path depending on your needs
                    let images_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("test_images");
                    info!("Saving image to: {images_dir:?}");
                    std::fs::create_dir_all(&images_dir).unwrap();

                    // Choose filename starting from 000.png
                    let image_path = images_dir.join(format!("{:03}.png", file_number.deref()));
                    *file_number.deref_mut() += 1;

                    // Finally saving image to file, this heavy blocking operation is kept here
                    // for example simplicity, but in real app you should move it to a separate task
                    if let Err(e) = img.save(image_path) {
                        panic!("Failed to save image: {e}");
                    };
                }
                if scene_controller.single_image {
                    app_exit_writer.write(AppExit::Success);
                }
            }
        } else {
            // clears channel for skipped frames
            while receiver.try_recv().is_ok() {}
            scene_controller.state = SceneState::Render(n - 1);
        }
    }
}

examples/stress_tests/many_animated_sprites.rs (line 143)

fn print_sprite_count(time: Res<Time>, mut timer: Local<PrintingTimer>, sprites: Query<&Sprite>) {
    timer.tick(time.delta());

    if timer.just_finished() {
        info!("Sprites: {}", sprites.iter().count());
    }
}

examples/stress_tests/many_sprites.rs (line 127)

fn print_sprite_count(time: Res<Time>, mut timer: Local<PrintingTimer>, sprites: Query<&Sprite>) {
    timer.tick(time.delta());

    if timer.just_finished() {
        info!("Sprites: {}", sprites.iter().count());
    }
}

examples/stress_tests/many_lights.rs (line 149)

fn print_light_count(time: Res<Time>, mut timer: Local<PrintingTimer>, lights: Query<&PointLight>) {
    timer.0.tick(time.delta());

    if timer.0.just_finished() {
        info!("Lights: {}", lights.iter().len());
    }
}

struct LogVisibleLights;

impl Plugin for LogVisibleLights {
    fn build(&self, app: &mut App) {
        let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
            return;
        };

        render_app.add_systems(Render, print_visible_light_count.in_set(RenderSet::Prepare));
    }
}

// System for printing the number of meshes on every tick of the timer
fn print_visible_light_count(
    time: Res<Time>,
    mut timer: Local<PrintingTimer>,
    visible: Query<&ExtractedPointLight>,
    global_light_meta: Res<GlobalClusterableObjectMeta>,
) {
    timer.0.tick(time.delta());

    if timer.0.just_finished() {
        info!(
            "Visible Lights: {}, Rendered Lights: {}",
            visible.iter().len(),
            global_light_meta.entity_to_index.len()
        );
    }
}

examples/ecs/one_shot_systems.rs (line 76)

fn evaluate_callbacks(query: Query<(Entity, &Callback), With<Triggered>>, mut commands: Commands) {
    for (entity, callback) in query.iter() {
        commands.run_system(callback.0);
        commands.entity(entity).remove::<Triggered>();
    }
}

Additional examples can be found in:

• examples/games/loading_screen.rs
• examples/ecs/observer_propagation.rs
• examples/ecs/removal_detection.rs
• examples/stress_tests/many_cubes.rs
• examples/asset/multi_asset_sync.rs
• examples/picking/mesh_picking.rs
• examples/3d/animated_material.rs
• examples/3d/reflection_probes.rs
• examples/window/screenshot.rs
• examples/3d/depth_of_field.rs
• examples/stress_tests/many_materials.rs
• examples/3d/specular_tint.rs
• examples/asset/asset_decompression.rs
• examples/stress_tests/many_text2d.rs
• examples/3d/visibility_range.rs
• examples/stress_tests/many_foxes.rs
• examples/ecs/entity_disabling.rs
• examples/3d/anisotropy.rs
• examples/math/sampling_primitives.rs
• examples/3d/irradiance_volumes.rs
• examples/math/bounding_2d.rs
• examples/3d/shadow_caster_receiver.rs
• examples/ecs/fallible_params.rs
• examples/ui/directional_navigation.rs
• examples/math/render_primitives.rs
• examples/math/custom_primitives.rs
• examples/3d/load_gltf_extras.rs
• examples/animation/animation_graph.rs
• examples/ecs/relationships.rs
• examples/3d/mixed_lighting.rs
• examples/3d/query_gltf_primitives.rs
• examples/audio/soundtrack.rs
• examples/3d/lightmaps.rs
• examples/stress_tests/many_components.rs
• examples/ui/size_constraints.rs
• examples/3d/color_grading.rs
• examples/3d/occlusion_culling.rs
• examples/window/monitor_info.rs
• examples/shader/custom_phase_item.rs
• examples/shader/specialized_mesh_pipeline.rs

pub fn iter_mut(&mut self) -> QueryIter<'_, 's, D, F>

Returns an Iterator over the query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

Example

Here, the gravity_system updates the Velocity component of every entity that contains it:

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;
    }
}

See also

iter for read-only query items.

Examples found in repository

examples/3d/irradiance_volumes.rs (line 306)

fn update_text(mut text_query: Query<&mut Text>, app_status: Res<AppStatus>) {
    for mut text in text_query.iter_mut() {
        *text = app_status.create_text();
    }
}

impl AppStatus {
    // Constructs the help text at the bottom of the screen based on the
    // application status.
    fn create_text(&self) -> Text {
        let irradiance_volume_help_text = if self.irradiance_volume_present {
            DISABLE_IRRADIANCE_VOLUME_HELP_TEXT
        } else {
            ENABLE_IRRADIANCE_VOLUME_HELP_TEXT
        };

        let voxels_help_text = if self.voxels_visible {
            HIDE_VOXELS_HELP_TEXT
        } else {
            SHOW_VOXELS_HELP_TEXT
        };

        let rotation_help_text = if self.rotating {
            STOP_ROTATION_HELP_TEXT
        } else {
            START_ROTATION_HELP_TEXT
        };

        let switch_mesh_help_text = match self.model {
            ExampleModel::Sphere => SWITCH_TO_FOX_HELP_TEXT,
            ExampleModel::Fox => SWITCH_TO_SPHERE_HELP_TEXT,
        };

        format!(
            "{CLICK_TO_MOVE_HELP_TEXT}\n\
            {voxels_help_text}\n\
            {irradiance_volume_help_text}\n\
            {rotation_help_text}\n\
            {switch_mesh_help_text}"
        )
        .into()
    }
}

// Rotates the camera a bit every frame.
fn rotate_camera(
    mut camera_query: Query<&mut Transform, With<Camera3d>>,
    time: Res<Time>,
    app_status: Res<AppStatus>,
) {
    if !app_status.rotating {
        return;
    }

    for mut transform in camera_query.iter_mut() {
        transform.translation = Vec2::from_angle(ROTATION_SPEED * time.delta_secs())
            .rotate(transform.translation.xz())
            .extend(transform.translation.y)
            .xzy();
        transform.look_at(Vec3::ZERO, Vec3::Y);
    }
}

// Toggles between the unskinned sphere model and the skinned fox model if the
// user requests it.
fn change_main_object(
    keyboard: Res<ButtonInput<KeyCode>>,
    mut app_status: ResMut<AppStatus>,
    mut sphere_query: Query<&mut Visibility, (With<MainObject>, With<Mesh3d>, Without<SceneRoot>)>,
    mut fox_query: Query<&mut Visibility, (With<MainObject>, With<SceneRoot>)>,
) {
    if !keyboard.just_pressed(KeyCode::Tab) {
        return;
    }
    let Some(mut sphere_visibility) = sphere_query.iter_mut().next() else {
        return;
    };
    let Some(mut fox_visibility) = fox_query.iter_mut().next() else {
        return;
    };

    match app_status.model {
        ExampleModel::Sphere => {
            *sphere_visibility = Visibility::Hidden;
            *fox_visibility = Visibility::Visible;
            app_status.model = ExampleModel::Fox;
        }
        ExampleModel::Fox => {
            *sphere_visibility = Visibility::Visible;
            *fox_visibility = Visibility::Hidden;
            app_status.model = ExampleModel::Sphere;
        }
    }
}

impl Default for AppStatus {
    fn default() -> Self {
        Self {
            irradiance_volume_present: true,
            rotating: true,
            model: ExampleModel::Sphere,
            voxels_visible: false,
        }
    }
}

// Turns on and off the irradiance volume as requested by the user.
fn toggle_irradiance_volumes(
    mut commands: Commands,
    keyboard: Res<ButtonInput<KeyCode>>,
    light_probe_query: Query<Entity, With<LightProbe>>,
    mut app_status: ResMut<AppStatus>,
    assets: Res<ExampleAssets>,
    mut ambient_light: ResMut<AmbientLight>,
) {
    if !keyboard.just_pressed(KeyCode::Space) {
        return;
    };

    let Some(light_probe) = light_probe_query.iter().next() else {
        return;
    };

    if app_status.irradiance_volume_present {
        commands.entity(light_probe).remove::<IrradianceVolume>();
        ambient_light.brightness = AMBIENT_LIGHT_BRIGHTNESS * IRRADIANCE_VOLUME_INTENSITY;
        app_status.irradiance_volume_present = false;
    } else {
        commands.entity(light_probe).insert(IrradianceVolume {
            voxels: assets.irradiance_volume.clone(),
            intensity: IRRADIANCE_VOLUME_INTENSITY,
            ..default()
        });
        ambient_light.brightness = 0.0;
        app_status.irradiance_volume_present = true;
    }
}

fn toggle_rotation(keyboard: Res<ButtonInput<KeyCode>>, mut app_status: ResMut<AppStatus>) {
    if keyboard.just_pressed(KeyCode::Enter) {
        app_status.rotating = !app_status.rotating;
    }
}

// Handles clicks on the plane that reposition the object.
fn handle_mouse_clicks(
    buttons: Res<ButtonInput<MouseButton>>,
    windows: Query<&Window, With<PrimaryWindow>>,
    cameras: Query<(&Camera, &GlobalTransform)>,
    mut main_objects: Query<&mut Transform, With<MainObject>>,
) {
    if !buttons.pressed(MouseButton::Left) {
        return;
    }
    let Some(mouse_position) = windows.iter().next().and_then(Window::cursor_position) else {
        return;
    };
    let Some((camera, camera_transform)) = cameras.iter().next() else {
        return;
    };

    // Figure out where the user clicked on the plane.
    let Ok(ray) = camera.viewport_to_world(camera_transform, mouse_position) else {
        return;
    };
    let Some(ray_distance) = ray.intersect_plane(Vec3::ZERO, InfinitePlane3d::new(Vec3::Y)) else {
        return;
    };
    let plane_intersection = ray.origin + ray.direction.normalize() * ray_distance;

    // Move all the main objects.
    for mut transform in main_objects.iter_mut() {
        transform.translation = vec3(
            plane_intersection.x,
            transform.translation.y,
            plane_intersection.z,
        );
    }
}

impl FromWorld for ExampleAssets {
    fn from_world(world: &mut World) -> Self {
        let fox_animation =
            world.load_asset(GltfAssetLabel::Animation(1).from_asset("models/animated/Fox.glb"));
        let (fox_animation_graph, fox_animation_node) =
            AnimationGraph::from_clip(fox_animation.clone());

        ExampleAssets {
            main_sphere: world.add_asset(Sphere::default().mesh().uv(32, 18)),
            fox: world.load_asset(GltfAssetLabel::Scene(0).from_asset("models/animated/Fox.glb")),
            main_sphere_material: world.add_asset(Color::from(SILVER)),
            main_scene: world.load_asset(
                GltfAssetLabel::Scene(0)
                    .from_asset("models/IrradianceVolumeExample/IrradianceVolumeExample.glb"),
            ),
            irradiance_volume: world.load_asset("irradiance_volumes/Example.vxgi.ktx2"),
            fox_animation_graph: world.add_asset(fox_animation_graph),
            fox_animation_node,
            voxel_cube: world.add_asset(Cuboid::default()),
            // Just use a specular map for the skybox since it's not too blurry.
            // In reality you wouldn't do this--you'd use a real skybox texture--but
            // reusing the textures like this saves space in the Bevy repository.
            skybox: world.load_asset("environment_maps/pisa_specular_rgb9e5_zstd.ktx2"),
        }
    }
}

// Plays the animation on the fox.
fn play_animations(
    mut commands: Commands,
    assets: Res<ExampleAssets>,
    mut players: Query<(Entity, &mut AnimationPlayer), Without<AnimationGraphHandle>>,
) {
    for (entity, mut player) in players.iter_mut() {
        commands
            .entity(entity)
            .insert(AnimationGraphHandle(assets.fox_animation_graph.clone()));
        player.play(assets.fox_animation_node).repeat();
    }
}

fn create_cubes(
    image_assets: Res<Assets<Image>>,
    mut commands: Commands,
    irradiance_volumes: Query<(&IrradianceVolume, &GlobalTransform)>,
    voxel_cube_parents: Query<Entity, With<VoxelCubeParent>>,
    voxel_cubes: Query<Entity, With<VoxelCube>>,
    example_assets: Res<ExampleAssets>,
    mut voxel_visualization_material_assets: ResMut<Assets<VoxelVisualizationMaterial>>,
) {
    // If voxel cubes have already been spawned, don't do anything.
    if !voxel_cubes.is_empty() {
        return;
    }

    let Some(voxel_cube_parent) = voxel_cube_parents.iter().next() else {
        return;
    };

    for (irradiance_volume, global_transform) in irradiance_volumes.iter() {
        let Some(image) = image_assets.get(&irradiance_volume.voxels) else {
            continue;
        };

        let resolution = image.texture_descriptor.size;

        let voxel_cube_material = voxel_visualization_material_assets.add(ExtendedMaterial {
            base: StandardMaterial::from(Color::from(RED)),
            extension: VoxelVisualizationExtension {
                irradiance_volume_info: VoxelVisualizationIrradianceVolumeInfo {
                    world_from_voxel: VOXEL_FROM_WORLD.inverse(),
                    voxel_from_world: VOXEL_FROM_WORLD,
                    resolution: uvec3(
                        resolution.width,
                        resolution.height,
                        resolution.depth_or_array_layers,
                    ),
                    intensity: IRRADIANCE_VOLUME_INTENSITY,
                },
            },
        });

        let scale = vec3(
            1.0 / resolution.width as f32,
            1.0 / resolution.height as f32,
            1.0 / resolution.depth_or_array_layers as f32,
        );

        // Spawn a cube for each voxel.
        for z in 0..resolution.depth_or_array_layers {
            for y in 0..resolution.height {
                for x in 0..resolution.width {
                    let uvw = (uvec3(x, y, z).as_vec3() + 0.5) * scale - 0.5;
                    let pos = global_transform.transform_point(uvw);
                    let voxel_cube = commands
                        .spawn((
                            Mesh3d(example_assets.voxel_cube.clone()),
                            MeshMaterial3d(voxel_cube_material.clone()),
                            Transform::from_scale(Vec3::splat(VOXEL_CUBE_SCALE))
                                .with_translation(pos),
                        ))
                        .insert(VoxelCube)
                        .insert(NotShadowCaster)
                        .id();

                    commands.entity(voxel_cube_parent).add_child(voxel_cube);
                }
            }
        }
    }
}

// Draws a gizmo showing the bounds of the irradiance volume.
fn draw_gizmo(
    mut gizmos: Gizmos,
    irradiance_volume_query: Query<&GlobalTransform, With<IrradianceVolume>>,
    app_status: Res<AppStatus>,
) {
    if app_status.voxels_visible {
        for transform in irradiance_volume_query.iter() {
            gizmos.cuboid(*transform, GIZMO_COLOR);
        }
    }
}

// Handles a request from the user to toggle the voxel visibility on and off.
fn toggle_voxel_visibility(
    keyboard: Res<ButtonInput<KeyCode>>,
    mut app_status: ResMut<AppStatus>,
    mut voxel_cube_parent_query: Query<&mut Visibility, With<VoxelCubeParent>>,
) {
    if !keyboard.just_pressed(KeyCode::Backspace) {
        return;
    }

    app_status.voxels_visible = !app_status.voxels_visible;

    for mut visibility in voxel_cube_parent_query.iter_mut() {
        *visibility = if app_status.voxels_visible {
            Visibility::Visible
        } else {
            Visibility::Hidden
        };
    }
}

examples/3d/reflection_probes.rs (line 237)

fn update_text(mut text_query: Query<&mut Text>, app_status: Res<AppStatus>) {
    for mut text in text_query.iter_mut() {
        *text = app_status.create_text();
    }
}

impl TryFrom<u32> for ReflectionMode {
    type Error = ();

    fn try_from(value: u32) -> Result<Self, Self::Error> {
        match value {
            0 => Ok(ReflectionMode::None),
            1 => Ok(ReflectionMode::EnvironmentMap),
            2 => Ok(ReflectionMode::ReflectionProbe),
            _ => Err(()),
        }
    }
}

impl Display for ReflectionMode {
    fn fmt(&self, formatter: &mut Formatter<'_>) -> FmtResult {
        let text = match *self {
            ReflectionMode::None => "No reflections",
            ReflectionMode::EnvironmentMap => "Environment map",
            ReflectionMode::ReflectionProbe => "Reflection probe",
        };
        formatter.write_str(text)
    }
}

impl AppStatus {
    // Constructs the help text at the bottom of the screen based on the
    // application status.
    fn create_text(&self) -> Text {
        let rotation_help_text = if self.rotating {
            STOP_ROTATION_HELP_TEXT
        } else {
            START_ROTATION_HELP_TEXT
        };

        format!(
            "{}\n{}\n{}",
            self.reflection_mode, rotation_help_text, REFLECTION_MODE_HELP_TEXT
        )
        .into()
    }
}

// Creates the world environment map light, used as a fallback if no reflection
// probe is applicable to a mesh.
fn create_camera_environment_map_light(cubemaps: &Cubemaps) -> EnvironmentMapLight {
    EnvironmentMapLight {
        diffuse_map: cubemaps.diffuse.clone(),
        specular_map: cubemaps.specular_environment_map.clone(),
        intensity: 5000.0,
        ..default()
    }
}

// Rotates the camera a bit every frame.
fn rotate_camera(
    time: Res<Time>,
    mut camera_query: Query<&mut Transform, With<Camera3d>>,
    app_status: Res<AppStatus>,
) {
    if !app_status.rotating {
        return;
    }

    for mut transform in camera_query.iter_mut() {
        transform.translation = Vec2::from_angle(time.delta_secs() * PI / 5.0)
            .rotate(transform.translation.xz())
            .extend(transform.translation.y)
            .xzy();
        transform.look_at(Vec3::ZERO, Vec3::Y);
    }
}

examples/3d/post_processing.rs (line 197)

fn update_help_text(mut text: Query<&mut Text>, app_settings: Res<AppSettings>) {
    for mut text in text.iter_mut() {
        *text = create_help_text(&app_settings);
    }
}

examples/3d/atmosphere.rs (line 123)

fn dynamic_scene(mut suns: Query<&mut Transform, With<DirectionalLight>>, time: Res<Time>) {
    suns.iter_mut()
        .for_each(|mut tf| tf.rotate_x(-time.delta_secs() * PI / 10.0));
}

examples/math/bounding_2d.rs (line 40)

fn spin(time: Res<Time>, mut query: Query<&mut Transform, With<Spin>>) {
    for mut transform in query.iter_mut() {
        transform.rotation *= Quat::from_rotation_z(time.delta_secs() / 5.);
    }
}

#[derive(States, Default, Debug, Hash, PartialEq, Eq, Clone, Copy)]
enum Test {
    AabbSweep,
    CircleSweep,
    #[default]
    RayCast,
    AabbCast,
    CircleCast,
}

fn update_test_state(
    keycode: Res<ButtonInput<KeyCode>>,
    cur_state: Res<State<Test>>,
    mut state: ResMut<NextState<Test>>,
) {
    if !keycode.just_pressed(KeyCode::Space) {
        return;
    }

    use Test::*;
    let next = match **cur_state {
        AabbSweep => CircleSweep,
        CircleSweep => RayCast,
        RayCast => AabbCast,
        AabbCast => CircleCast,
        CircleCast => AabbSweep,
    };
    state.set(next);
}

fn update_text(mut text: Single<&mut Text>, cur_state: Res<State<Test>>) {
    if !cur_state.is_changed() {
        return;
    }

    text.clear();

    text.push_str("Intersection test:\n");
    use Test::*;
    for &test in &[AabbSweep, CircleSweep, RayCast, AabbCast, CircleCast] {
        let s = if **cur_state == test { "*" } else { " " };
        text.push_str(&format!(" {s} {test:?} {s}\n"));
    }
    text.push_str("\nPress space to cycle");
}

#[derive(Component)]
enum Shape {
    Rectangle(Rectangle),
    Circle(Circle),
    Triangle(Triangle2d),
    Line(Segment2d),
    Capsule(Capsule2d),
    Polygon(RegularPolygon),
}

fn render_shapes(mut gizmos: Gizmos, query: Query<(&Shape, &Transform)>) {
    let color = GRAY;
    for (shape, transform) in query.iter() {
        let translation = transform.translation.xy();
        let rotation = transform.rotation.to_euler(EulerRot::YXZ).2;
        let isometry = Isometry2d::new(translation, Rot2::radians(rotation));
        match shape {
            Shape::Rectangle(r) => {
                gizmos.primitive_2d(r, isometry, color);
            }
            Shape::Circle(c) => {
                gizmos.primitive_2d(c, isometry, color);
            }
            Shape::Triangle(t) => {
                gizmos.primitive_2d(t, isometry, color);
            }
            Shape::Line(l) => {
                gizmos.primitive_2d(l, isometry, color);
            }
            Shape::Capsule(c) => {
                gizmos.primitive_2d(c, isometry, color);
            }
            Shape::Polygon(p) => {
                gizmos.primitive_2d(p, isometry, color);
            }
        }
    }
}

#[derive(Component)]
enum DesiredVolume {
    Aabb,
    Circle,
}

#[derive(Component, Debug)]
enum CurrentVolume {
    Aabb(Aabb2d),
    Circle(BoundingCircle),
}

fn update_volumes(
    mut commands: Commands,
    query: Query<
        (Entity, &DesiredVolume, &Shape, &Transform),
        Or<(Changed<DesiredVolume>, Changed<Shape>, Changed<Transform>)>,
    >,
) {
    for (entity, desired_volume, shape, transform) in query.iter() {
        let translation = transform.translation.xy();
        let rotation = transform.rotation.to_euler(EulerRot::YXZ).2;
        let isometry = Isometry2d::new(translation, Rot2::radians(rotation));
        match desired_volume {
            DesiredVolume::Aabb => {
                let aabb = match shape {
                    Shape::Rectangle(r) => r.aabb_2d(isometry),
                    Shape::Circle(c) => c.aabb_2d(isometry),
                    Shape::Triangle(t) => t.aabb_2d(isometry),
                    Shape::Line(l) => l.aabb_2d(isometry),
                    Shape::Capsule(c) => c.aabb_2d(isometry),
                    Shape::Polygon(p) => p.aabb_2d(isometry),
                };
                commands.entity(entity).insert(CurrentVolume::Aabb(aabb));
            }
            DesiredVolume::Circle => {
                let circle = match shape {
                    Shape::Rectangle(r) => r.bounding_circle(isometry),
                    Shape::Circle(c) => c.bounding_circle(isometry),
                    Shape::Triangle(t) => t.bounding_circle(isometry),
                    Shape::Line(l) => l.bounding_circle(isometry),
                    Shape::Capsule(c) => c.bounding_circle(isometry),
                    Shape::Polygon(p) => p.bounding_circle(isometry),
                };
                commands
                    .entity(entity)
                    .insert(CurrentVolume::Circle(circle));
            }
        }
    }
}

fn render_volumes(mut gizmos: Gizmos, query: Query<(&CurrentVolume, &Intersects)>) {
    for (volume, intersects) in query.iter() {
        let color = if **intersects { AQUA } else { ORANGE_RED };
        match volume {
            CurrentVolume::Aabb(a) => {
                gizmos.rect_2d(a.center(), a.half_size() * 2., color);
            }
            CurrentVolume::Circle(c) => {
                gizmos.circle_2d(c.center(), c.radius(), color);
            }
        }
    }
}

#[derive(Component, Deref, DerefMut, Default)]
struct Intersects(bool);

const OFFSET_X: f32 = 125.;
const OFFSET_Y: f32 = 75.;

fn setup(mut commands: Commands) {
    commands.spawn(Camera2d);

    commands.spawn((
        Transform::from_xyz(-OFFSET_X, OFFSET_Y, 0.),
        Shape::Circle(Circle::new(45.)),
        DesiredVolume::Aabb,
        Intersects::default(),
    ));

    commands.spawn((
        Transform::from_xyz(0., OFFSET_Y, 0.),
        Shape::Rectangle(Rectangle::new(80., 80.)),
        Spin,
        DesiredVolume::Circle,
        Intersects::default(),
    ));

    commands.spawn((
        Transform::from_xyz(OFFSET_X, OFFSET_Y, 0.),
        Shape::Triangle(Triangle2d::new(
            Vec2::new(-40., -40.),
            Vec2::new(-20., 40.),
            Vec2::new(40., 50.),
        )),
        Spin,
        DesiredVolume::Aabb,
        Intersects::default(),
    ));

    commands.spawn((
        Transform::from_xyz(-OFFSET_X, -OFFSET_Y, 0.),
        Shape::Line(Segment2d::from_direction_and_length(
            Dir2::from_xy(1., 0.3).unwrap(),
            90.,
        )),
        Spin,
        DesiredVolume::Circle,
        Intersects::default(),
    ));

    commands.spawn((
        Transform::from_xyz(0., -OFFSET_Y, 0.),
        Shape::Capsule(Capsule2d::new(25., 50.)),
        Spin,
        DesiredVolume::Aabb,
        Intersects::default(),
    ));

    commands.spawn((
        Transform::from_xyz(OFFSET_X, -OFFSET_Y, 0.),
        Shape::Polygon(RegularPolygon::new(50., 6)),
        Spin,
        DesiredVolume::Circle,
        Intersects::default(),
    ));

    commands.spawn((
        Text::default(),
        Node {
            position_type: PositionType::Absolute,
            top: Val::Px(12.0),
            left: Val::Px(12.0),
            ..default()
        },
    ));
}

fn draw_filled_circle(gizmos: &mut Gizmos, position: Vec2, color: Srgba) {
    for r in [1., 2., 3.] {
        gizmos.circle_2d(position, r, color);
    }
}

fn draw_ray(gizmos: &mut Gizmos, ray: &RayCast2d) {
    gizmos.line_2d(
        ray.ray.origin,
        ray.ray.origin + *ray.ray.direction * ray.max,
        WHITE,
    );
    draw_filled_circle(gizmos, ray.ray.origin, FUCHSIA);
}

fn get_and_draw_ray(gizmos: &mut Gizmos, time: &Time) -> RayCast2d {
    let ray = Vec2::new(ops::cos(time.elapsed_secs()), ops::sin(time.elapsed_secs()));
    let dist = 150. + ops::sin(0.5 * time.elapsed_secs()).abs() * 500.;

    let aabb_ray = Ray2d {
        origin: ray * 250.,
        direction: Dir2::new_unchecked(-ray),
    };
    let ray_cast = RayCast2d::from_ray(aabb_ray, dist - 20.);

    draw_ray(gizmos, &ray_cast);
    ray_cast
}

fn ray_cast_system(
    mut gizmos: Gizmos,
    time: Res<Time>,
    mut volumes: Query<(&CurrentVolume, &mut Intersects)>,
) {
    let ray_cast = get_and_draw_ray(&mut gizmos, &time);

    for (volume, mut intersects) in volumes.iter_mut() {
        let toi = match volume {
            CurrentVolume::Aabb(a) => ray_cast.aabb_intersection_at(a),
            CurrentVolume::Circle(c) => ray_cast.circle_intersection_at(c),
        };
        **intersects = toi.is_some();
        if let Some(toi) = toi {
            draw_filled_circle(
                &mut gizmos,
                ray_cast.ray.origin + *ray_cast.ray.direction * toi,
                LIME,
            );
        }
    }
}

fn aabb_cast_system(
    mut gizmos: Gizmos,
    time: Res<Time>,
    mut volumes: Query<(&CurrentVolume, &mut Intersects)>,
) {
    let ray_cast = get_and_draw_ray(&mut gizmos, &time);
    let aabb_cast = AabbCast2d {
        aabb: Aabb2d::new(Vec2::ZERO, Vec2::splat(15.)),
        ray: ray_cast,
    };

    for (volume, mut intersects) in volumes.iter_mut() {
        let toi = match *volume {
            CurrentVolume::Aabb(a) => aabb_cast.aabb_collision_at(a),
            CurrentVolume::Circle(_) => None,
        };

        **intersects = toi.is_some();
        if let Some(toi) = toi {
            gizmos.rect_2d(
                aabb_cast.ray.ray.origin + *aabb_cast.ray.ray.direction * toi,
                aabb_cast.aabb.half_size() * 2.,
                LIME,
            );
        }
    }
}

fn bounding_circle_cast_system(
    mut gizmos: Gizmos,
    time: Res<Time>,
    mut volumes: Query<(&CurrentVolume, &mut Intersects)>,
) {
    let ray_cast = get_and_draw_ray(&mut gizmos, &time);
    let circle_cast = BoundingCircleCast {
        circle: BoundingCircle::new(Vec2::ZERO, 15.),
        ray: ray_cast,
    };

    for (volume, mut intersects) in volumes.iter_mut() {
        let toi = match *volume {
            CurrentVolume::Aabb(_) => None,
            CurrentVolume::Circle(c) => circle_cast.circle_collision_at(c),
        };

        **intersects = toi.is_some();
        if let Some(toi) = toi {
            gizmos.circle_2d(
                circle_cast.ray.ray.origin + *circle_cast.ray.ray.direction * toi,
                circle_cast.circle.radius(),
                LIME,
            );
        }
    }
}

fn get_intersection_position(time: &Time) -> Vec2 {
    let x = ops::cos(0.8 * time.elapsed_secs()) * 250.;
    let y = ops::sin(0.4 * time.elapsed_secs()) * 100.;
    Vec2::new(x, y)
}

fn aabb_intersection_system(
    mut gizmos: Gizmos,
    time: Res<Time>,
    mut volumes: Query<(&CurrentVolume, &mut Intersects)>,
) {
    let center = get_intersection_position(&time);
    let aabb = Aabb2d::new(center, Vec2::splat(50.));
    gizmos.rect_2d(center, aabb.half_size() * 2., YELLOW);

    for (volume, mut intersects) in volumes.iter_mut() {
        let hit = match volume {
            CurrentVolume::Aabb(a) => aabb.intersects(a),
            CurrentVolume::Circle(c) => aabb.intersects(c),
        };

        **intersects = hit;
    }
}

fn circle_intersection_system(
    mut gizmos: Gizmos,
    time: Res<Time>,
    mut volumes: Query<(&CurrentVolume, &mut Intersects)>,
) {
    let center = get_intersection_position(&time);
    let circle = BoundingCircle::new(center, 50.);
    gizmos.circle_2d(center, circle.radius(), YELLOW);

    for (volume, mut intersects) in volumes.iter_mut() {
        let hit = match volume {
            CurrentVolume::Aabb(a) => circle.intersects(a),
            CurrentVolume::Circle(c) => circle.intersects(c),
        };

        **intersects = hit;
    }
}

examples/3d/scrolling_fog.rs (line 127)

fn scroll_fog(time: Res<Time>, mut query: Query<&mut FogVolume>) {
    for mut fog_volume in query.iter_mut() {
        fog_volume.density_texture_offset += Vec3::new(0.0, 0.0, 0.04) * time.delta_secs();
    }
}

Additional examples can be found in:

• examples/stress_tests/many_cameras_lights.rs
• examples/shader/shader_prepass.rs
• examples/stress_tests/text_pipeline.rs
• examples/math/custom_primitives.rs
• examples/3d/bloom_3d.rs
• examples/3d/ssr.rs
• examples/3d/specular_tint.rs
• examples/shader/automatic_instancing.rs
• examples/3d/fog_volumes.rs
• examples/ui/directional_navigation.rs
• examples/3d/parallax_mapping.rs
• examples/3d/anisotropy.rs
• examples/3d/volumetric_fog.rs
• examples/math/cubic_splines.rs
• examples/3d/rotate_environment_map.rs
• examples/3d/camera_sub_view.rs
• examples/3d/deferred_rendering.rs
• examples/input/text_input.rs
• examples/ui/overflow.rs
• examples/3d/clearcoat.rs
• examples/3d/color_grading.rs
• examples/3d/../helpers/widgets.rs
• examples/audio/soundtrack.rs
• examples/time/virtual_time.rs
• examples/3d/spotlight.rs
• examples/ui/tab_navigation.rs
• examples/stress_tests/many_animated_sprites.rs
• examples/animation/animation_graph.rs
• examples/shader/shader_material_wesl.rs
• examples/ui/viewport_debug.rs
• examples/audio/spatial_audio_2d.rs
• examples/3d/tonemapping.rs
• examples/audio/spatial_audio_3d.rs
• examples/math/render_primitives.rs
• examples/window/window_drag_move.rs
• examples/3d/depth_of_field.rs
• examples/3d/pcss.rs
• examples/ui/display_and_visibility.rs
• examples/movement/physics_in_fixed_timestep.rs
• examples/testbed/full_ui.rs
• examples/3d/visibility_range.rs
• examples/3d/mixed_lighting.rs
• examples/animation/animation_masks.rs
• examples/games/alien_cake_addict.rs
• examples/camera/2d_screen_shake.rs
• examples/stress_tests/many_buttons.rs
• examples/ui/size_constraints.rs
• examples/math/sampling_primitives.rs

pub fn iter_combinations<const K: usize>( &self, ) -> QueryCombinationIter<'_, 's, <D as QueryData>::ReadOnly, F, K>

Returns a QueryCombinationIter over all combinations of K read-only query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Example

fn some_system(query: Query<&ComponentA>) {
    for [a1, a2] in query.iter_combinations() {
        // ...
    }
}

See also

• iter_combinations_mut for mutable query item combinations.
• iter_combinations_inner for mutable query item combinations with the full 'world lifetime.

pub fn iter_combinations_mut<const K: usize>( &mut self, ) -> QueryCombinationIter<'_, 's, D, F, K>

Returns a QueryCombinationIter over all combinations of K query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Example

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 for read-only query item combinations.
• iter_combinations_inner for mutable query item combinations with the full 'world lifetime.

Examples found in repository

examples/ecs/iter_combinations.rs (line 123)

fn interact_bodies(mut query: Query<(&Mass, &GlobalTransform, &mut Acceleration)>) {
    let mut iter = query.iter_combinations_mut();
    while let Some([(Mass(m1), transform1, mut acc1), (Mass(m2), transform2, mut acc2)]) =
        iter.fetch_next()
    {
        let delta = transform2.translation() - transform1.translation();
        let distance_sq: f32 = delta.length_squared();

        let f = GRAVITY_CONSTANT / distance_sq;
        let force_unit_mass = delta * f;
        acc1.0 += force_unit_mass * *m2;
        acc2.0 -= force_unit_mass * *m1;
    }
}

pub fn iter_combinations_inner<const K: usize>( self, ) -> QueryCombinationIter<'w, 's, D, F, K>

Returns a QueryCombinationIter over all combinations of K query items without repetition. This consumes the Query to return results with the actual “inner” world lifetime.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

Example

fn some_system(query: Query<&mut ComponentA>) {
    let mut combinations = query.iter_combinations_inner();
    while let Some([mut a1, mut a2]) = combinations.fetch_next() {
        // mutably access components data
    }
}

See also

• iter_combinations for read-only query item combinations.
• iter_combinations_mut for mutable query item combinations.

pub fn iter_many<EntityList>( &self, entities: EntityList, ) -> QueryManyIter<'_, 's, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns an Iterator over the read-only query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Example

// 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);
        }
    }
}

See also

• iter_many_mut to get mutable query items.
• iter_many_inner to get mutable query items with the full 'world lifetime.

pub fn iter_many_mut<EntityList>( &mut self, entities: EntityList, ) -> QueryManyIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns an iterator over the query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesn’t guarantee uniqueness. Entities that don’t match the query are skipped.

Examples

#[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;
        }
    }
}

See also

• iter_many to get read-only query items.
• iter_many_inner to get mutable query items with the full 'world lifetime.

Examples found in repository

examples/animation/animation_graph.rs (line 427)

fn update_ui(
    mut text_query: Query<&mut Text>,
    mut background_query: Query<&mut Node, Without<Text>>,
    container_query: Query<(&Children, &ClipNode)>,
    animation_weights_query: Query<&ExampleAnimationWeights, Changed<ExampleAnimationWeights>>,
) {
    for animation_weights in animation_weights_query.iter() {
        for (children, clip_node) in &container_query {
            // Draw the green background color to visually indicate the weight.
            let mut bg_iter = background_query.iter_many_mut(children);
            if let Some(mut node) = bg_iter.fetch_next() {
                // All nodes are the same width, so `NODE_RECTS[0]` is as good as any other.
                node.width =
                    Val::Px(NODE_RECTS[0].width * animation_weights.weights[clip_node.index]);
            }

            // Update the node labels with the current weights.
            let mut text_iter = text_query.iter_many_mut(children);
            if let Some(mut text) = text_iter.fetch_next() {
                **text = format!(
                    "{}\n{:.2}",
                    clip_node.text, animation_weights.weights[clip_node.index]
                );
            }
        }
    }
}

pub fn iter_many_inner<EntityList>( self, entities: EntityList, ) -> QueryManyIter<'w, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns an iterator over the query items generated from an Entity list. This consumes the Query to return results with the actual “inner” world lifetime.

Items are returned in the order of the list of entities, and may not be unique if the input doesn’t guarantee uniqueness. Entities that don’t match the query are skipped.

See also

• iter_many to get read-only query items.
• iter_many_mut to get mutable query items.

pub fn iter_many_unique<EntityList>( &self, entities: EntityList, ) -> QueryManyUniqueIter<'_, 's, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: EntitySet,

Returns an Iterator over the unique read-only query items generated from an EntitySet.

Items are returned in the order of the list of entities. Entities that don’t match the query are skipped.

Example

// `Friends` ensures that it only lists unique entities.
#[derive(Component)]
struct Friends {
    unique_list: Vec<Entity>,
}

impl<'a> IntoIterator for &'a Friends {

    type Item = &'a Entity;
    type IntoIter = UniqueEntityIter<slice::Iter<'a, Entity>>;
  
    fn into_iter(self) -> Self::IntoIter {
        // SAFETY: `Friends` ensures that it unique_list contains only unique entities.
       unsafe { UniqueEntityIter::from_iterator_unchecked(self.unique_list.iter()) }
    }
}

fn system(
    friends_query: Query<&Friends>,
    counter_query: Query<&Counter>,
) {
    for friends in &friends_query {
        for counter in counter_query.iter_many_unique(friends) {
            println!("Friend's counter: {:?}", counter.value);
        }
    }
}

See also

• iter_many_unique_mut to get mutable query items.
• iter_many_unique_inner to get with the actual “inner” world lifetime.

pub fn iter_many_unique_mut<EntityList>( &mut self, entities: EntityList, ) -> QueryManyUniqueIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: EntitySet,

Returns an iterator over the unique query items generated from an EntitySet.

Items are returned in the order of the list of entities. Entities that don’t match the query are skipped.

Examples

#[derive(Component)]
struct Counter {
    value: i32
}

// `Friends` ensures that it only lists unique entities.
#[derive(Component)]
struct Friends {
    unique_list: Vec<Entity>,
}

impl<'a> IntoIterator for &'a Friends {
    type Item = &'a Entity;
    type IntoIter = UniqueEntityIter<slice::Iter<'a, Entity>>;

    fn into_iter(self) -> Self::IntoIter {
        // SAFETY: `Friends` ensures that it unique_list contains only unique entities.
        unsafe { UniqueEntityIter::from_iterator_unchecked(self.unique_list.iter()) }
    }
}

fn system(
    friends_query: Query<&Friends>,
    mut counter_query: Query<&mut Counter>,
) {
    for friends in &friends_query {
        for mut counter in counter_query.iter_many_unique_mut(friends) {
            println!("Friend's counter: {:?}", counter.value);
            counter.value += 1;
        }
    }
}

See also

• iter_many_unique to get read-only query items.
• iter_many_unique_inner to get with the actual “inner” world lifetime.

pub fn iter_many_unique_inner<EntityList>( self, entities: EntityList, ) -> QueryManyUniqueIter<'w, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: EntitySet,

Returns an iterator over the unique query items generated from an EntitySet. This consumes the Query to return results with the actual “inner” world lifetime.

Items are returned in the order of the list of entities. Entities that don’t match the query are skipped.

Examples

#[derive(Component)]
struct Counter {
    value: i32
}

// `Friends` ensures that it only lists unique entities.
#[derive(Component)]
struct Friends {
    unique_list: Vec<Entity>,
}

impl<'a> IntoIterator for &'a Friends {
    type Item = &'a Entity;
    type IntoIter = UniqueEntityIter<slice::Iter<'a, Entity>>;

    fn into_iter(self) -> Self::IntoIter {
        // SAFETY: `Friends` ensures that it unique_list contains only unique entities.
        unsafe { UniqueEntityIter::from_iterator_unchecked(self.unique_list.iter()) }
    }
}

fn system(
    friends_query: Query<&Friends>,
    mut counter_query: Query<&mut Counter>,
) {
    let friends = friends_query.single().unwrap();
    for mut counter in counter_query.iter_many_unique_inner(friends) {
        println!("Friend's counter: {:?}", counter.value);
        counter.value += 1;
    }
}

See also

• iter_many_unique to get read-only query items.
• iter_many_unique_mut to get mutable query items.

pub unsafe fn iter_unsafe(&self) -> QueryIter<'_, 's, D, F>

Returns an Iterator over the query items.

This iterator is always guaranteed to return results from each matching entity once and only once. Iteration order is not guaranteed.

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 and iter_mut for the safe versions.

pub unsafe fn iter_combinations_unsafe<const K: usize>( &self, ) -> QueryCombinationIter<'_, 's, D, F, K>

Iterates over all possible combinations of K query items without repetition.

This iterator is always guaranteed to return results from each unique pair of matching entities. Iteration order is not guaranteed.

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 and iter_combinations_mut for the safe versions.

pub unsafe fn iter_many_unsafe<EntityList>( &self, entities: EntityList, ) -> QueryManyIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns an Iterator over the query items generated from an Entity list.

Items are returned in the order of the list of entities, and may not be unique if the input doesnn’t guarantee uniqueness. Entities that don’t match the query are skipped.

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 to safely access the query items.

pub unsafe fn iter_many_unique_unsafe<EntityList>( &self, entities: EntityList, ) -> QueryManyUniqueIter<'_, 's, D, F, <EntityList as IntoIterator>::IntoIter>

where EntityList: EntitySet,

Returns an Iterator over the unique query items generated from an Entity list.

Items are returned in the order of the list of entities. Entities that don’t match the query are skipped.

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_many_unique to get read-only query items.
• iter_many_unique_mut to get mutable query items.
• iter_many_unique_inner to get with the actual “inner” world lifetime.

pub fn par_iter(&self) -> QueryParIter<'_, '_, <D as QueryData>::ReadOnly, F>

Returns a parallel iterator over the query results for the given World.

This parallel iterator is always guaranteed to return results from each matching entity once and only once. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryIter.

This can only be called for read-only queries, see par_iter_mut for write-queries.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn par_iter_mut(&mut self) -> QueryParIter<'_, '_, D, F>

Returns a parallel iterator over the query results for the given World.

This parallel iterator is always guaranteed to return results from each matching entity once and only once. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryIter.

This can only be called for mutable queries, see par_iter for read-only-queries.

Example

Here, the gravity_system updates the Velocity component of every entity that contains it:

fn gravity_system(mut query: Query<&mut Velocity>) {
    const DELTA: f32 = 1.0 / 60.0;
    query.par_iter_mut().for_each(|mut velocity| {
        velocity.y -= 9.8 * DELTA;
    });
}

Examples found in repository

examples/ecs/parallel_query.rs (line 38)

fn move_system(mut sprites: Query<(&mut Transform, &Velocity)>) {
    // Compute the new location of each sprite in parallel on the
    // ComputeTaskPool
    //
    // This example is only for demonstrative purposes. Using a
    // ParallelIterator for an inexpensive operation like addition on only 128
    // elements will not typically be faster than just using a normal Iterator.
    // See the ParallelIterator documentation for more information on when
    // to use or not use ParallelIterator over a normal Iterator.
    sprites
        .par_iter_mut()
        .for_each(|(mut transform, velocity)| {
            transform.translation += velocity.extend(0.0);
        });
}

// Bounce sprites outside the window
fn bounce_system(window: Query<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
    let Ok(window) = window.single() else {
        return;
    };
    let width = window.width();
    let height = window.height();
    let left = width / -2.0;
    let right = width / 2.0;
    let bottom = height / -2.0;
    let top = height / 2.0;
    // The default batch size can also be overridden.
    // In this case a batch size of 32 is chosen to limit the overhead of
    // ParallelIterator, since negating a vector is very inexpensive.
    sprites
        .par_iter_mut()
        .batching_strategy(BatchingStrategy::fixed(32))
        .for_each(|(transform, mut v)| {
            if !(left < transform.translation.x
                && transform.translation.x < right
                && bottom < transform.translation.y
                && transform.translation.y < top)
            {
                // For simplicity, just reverse the velocity; don't use realistic bounces
                v.0 = -v.0;
            }
        });
}

pub fn par_iter_inner(self) -> QueryParIter<'w, 's, D, F>

Returns a parallel iterator over the query results for the given World. This consumes the Query to return results with the actual “inner” world lifetime.

This parallel iterator is always guaranteed to return results from each matching entity once and only once. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryIter.

Example

Here, the gravity_system updates the Velocity component of every entity that contains it:

fn gravity_system(query: Query<&mut Velocity>) {
    const DELTA: f32 = 1.0 / 60.0;
    query.par_iter_inner().for_each(|mut velocity| {
        velocity.y -= 9.8 * DELTA;
    });
}

pub fn par_iter_many<EntityList>( &self, entities: EntityList, ) -> QueryParManyIter<'_, '_, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::Item>

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: EntityEquivalent,

Returns a parallel iterator over the read-only query items generated from an Entity list.

Entities that don’t match the query are skipped. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryManyIter.

This can only be called for read-only queries. To avoid potential aliasing, there is no par_iter_many_mut equivalent. See par_iter_many_unique_mut for an alternative using EntitySet.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn par_iter_many_unique<EntityList>( &self, entities: EntityList, ) -> QueryParManyUniqueIter<'_, '_, <D as QueryData>::ReadOnly, F, <EntityList as IntoIterator>::Item>

where EntityList: EntitySet, <EntityList as IntoIterator>::Item: Sync,

Returns a parallel iterator over the unique read-only query items generated from an EntitySet.

Entities that don’t match the query are skipped. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryManyUniqueIter.

This can only be called for read-only queries, see par_iter_many_unique_mut for write-queries.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn par_iter_many_unique_mut<EntityList>( &mut self, entities: EntityList, ) -> QueryParManyUniqueIter<'_, '_, D, F, <EntityList as IntoIterator>::Item>

where EntityList: EntitySet, <EntityList as IntoIterator>::Item: Sync,

Returns a parallel iterator over the unique query items generated from an EntitySet.

Entities that don’t match the query are skipped. Iteration order and thread assignment is not guaranteed.

If the multithreaded feature is disabled, iterating with this operates identically to Iterator::for_each on QueryManyUniqueIter.

This can only be called for mutable queries, see par_iter_many_unique for read-only-queries.

Note that you must use the for_each method to iterate over the results, see par_iter_mut for an example.

pub fn get( &self, entity: Entity, ) -> Result<<<D as QueryData>::ReadOnly as QueryData>::Item<'_>, QueryEntityError>

Returns the read-only query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Example

Here, get is used to retrieve the exact query item of the entity specified by the SelectedCharacter resource.

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);
    }
}

See also

• get_mut to get a mutable query item.

Examples found in repository

examples/ecs/observer_propagation.rs (line 81)

fn attack_hits(trigger: Trigger<Attack>, name: Query<&Name>) {
    if let Ok(name) = name.get(trigger.target()) {
        info!("Attack hit {}", name);
    }
}

/// A callback placed on [`Armor`], checking if it absorbed all the [`Attack`] damage.
fn block_attack(mut trigger: Trigger<Attack>, armor: Query<(&Armor, &Name)>) {
    let (armor, name) = armor.get(trigger.target()).unwrap();
    let attack = trigger.event_mut();
    let damage = attack.damage.saturating_sub(**armor);
    if damage > 0 {
        info!("🩸 {} damage passed through {}", damage, name);
        // The attack isn't stopped by the armor. We reduce the damage of the attack, and allow
        // it to continue on to the goblin.
        attack.damage = damage;
    } else {
        info!("🛡️  {} damage blocked by {}", attack.damage, name);
        // Armor stopped the attack, the event stops here.
        trigger.propagate(false);
        info!("(propagation halted early)\n");
    }
}

examples/ui/ghost_nodes.rs (line 120)

fn button_system(
    mut interaction_query: Query<(&Interaction, &ChildOf), (Changed<Interaction>, With<Button>)>,
    labels_query: Query<(&Children, &ChildOf), With<Button>>,
    mut text_query: Query<&mut Text>,
    mut counter_query: Query<&mut Counter>,
) {
    // Update parent counter on click
    for (interaction, child_of) in &mut interaction_query {
        if matches!(interaction, Interaction::Pressed) {
            let mut counter = counter_query.get_mut(child_of.parent()).unwrap();
            counter.0 += 1;
        }
    }

    // Update button labels to match their parent counter
    for (children, child_of) in &labels_query {
        let counter = counter_query.get(child_of.parent()).unwrap();
        let mut text = text_query.get_mut(children[0]).unwrap();

        **text = counter.0.to_string();
    }
}

examples/animation/animation_masks.rs (line 481)

fn update_ui(
    mut animation_controls: Query<(&AnimationControl, &mut BackgroundColor, &Children)>,
    texts: Query<Entity, With<Text>>,
    mut writer: TextUiWriter,
    app_state: Res<AppState>,
) {
    for (animation_control, mut background_color, kids) in animation_controls.iter_mut() {
        let enabled =
            app_state.0[animation_control.group_id as usize].clip == animation_control.label as u8;

        *background_color = if enabled {
            BackgroundColor(Color::WHITE)
        } else {
            BackgroundColor(Color::BLACK)
        };

        for &kid in kids {
            let Ok(text) = texts.get(kid) else {
                continue;
            };

            writer.for_each_color(text, |mut color| {
                color.0 = if enabled { Color::BLACK } else { Color::WHITE };
            });
        }
    }
}

examples/3d/split_screen.rs (line 171)

fn set_camera_viewports(
    windows: Query<&Window>,
    mut resize_events: EventReader<WindowResized>,
    mut query: Query<(&CameraPosition, &mut Camera)>,
) {
    // We need to dynamically resize the camera's viewports whenever the window size changes
    // so then each camera always takes up half the screen.
    // A resize_event is sent when the window is first created, allowing us to reuse this system for initial setup.
    for resize_event in resize_events.read() {
        let window = windows.get(resize_event.window).unwrap();
        let size = window.physical_size() / 2;

        for (camera_position, mut camera) in &mut query {
            camera.viewport = Some(Viewport {
                physical_position: camera_position.pos * size,
                physical_size: size,
                ..default()
            });
        }
    }
}

examples/animation/gltf_skinned_mesh.rs (line 56)

fn joint_animation(
    time: Res<Time>,
    children: Query<&ChildOf, With<SkinnedMesh>>,
    parents: Query<&Children>,
    mut transform_query: Query<&mut Transform>,
) {
    // Iter skinned mesh entity
    for child_of in &children {
        // Mesh node is the parent of the skinned mesh entity.
        let mesh_node_entity = child_of.parent();
        // Get `Children` in the mesh node.
        let mesh_node_parent = parents.get(mesh_node_entity).unwrap();

        // First joint is the second child of the mesh node.
        let first_joint_entity = mesh_node_parent[1];
        // Get `Children` in the first joint.
        let first_joint_children = parents.get(first_joint_entity).unwrap();

        // Second joint is the first child of the first joint.
        let second_joint_entity = first_joint_children[0];
        // Get `Transform` in the second joint.
        let mut second_joint_transform = transform_query.get_mut(second_joint_entity).unwrap();

        second_joint_transform.rotation =
            Quat::from_rotation_z(FRAC_PI_2 * ops::sin(time.elapsed_secs()));
    }
}

examples/animation/animated_mesh_events.rs (line 50)

fn observe_on_step(
    trigger: Trigger<OnStep>,
    particle: Res<ParticleAssets>,
    mut commands: Commands,
    transforms: Query<&GlobalTransform>,
    mut seeded_rng: ResMut<SeededRng>,
) {
    let translation = transforms.get(trigger.target()).unwrap().translation();
    // Spawn a bunch of particles.
    for _ in 0..14 {
        let horizontal = seeded_rng.0.r#gen::<Dir2>() * seeded_rng.0.gen_range(8.0..12.0);
        let vertical = seeded_rng.0.gen_range(0.0..4.0);
        let size = seeded_rng.0.gen_range(0.2..1.0);

        commands.spawn((
            Particle {
                lifetime_timer: Timer::from_seconds(
                    seeded_rng.0.gen_range(0.2..0.6),
                    TimerMode::Once,
                ),
                size,
                velocity: Vec3::new(horizontal.x, vertical, horizontal.y) * 10.0,
            },
            Mesh3d(particle.mesh.clone()),
            MeshMaterial3d(particle.material.clone()),
            Transform {
                translation,
                scale: Vec3::splat(size),
                ..Default::default()
            },
        ));
    }
}

Additional examples can be found in:

• examples/ecs/relationships.rs
• examples/3d/visibility_range.rs
• examples/3d/edit_material_on_gltf.rs
• examples/ecs/observers.rs
• examples/animation/animated_mesh.rs
• examples/games/alien_cake_addict.rs
• examples/3d/blend_modes.rs
• examples/ui/size_constraints.rs
• examples/shader/custom_render_phase.rs

pub fn get_many<const N: usize>( &self, entities: [Entity; N], ) -> Result<[<<D as QueryData>::ReadOnly as QueryData>::Item<'_>; N], QueryEntityError>

Returns the read-only query items for the given array of Entity.

The returned query items are in the same order as the input. 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.

Examples

use bevy_ecs::prelude::*;
use bevy_ecs::query::QueryEntityError;

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();
let entity_vec: Vec<Entity> = (0..3).map(|i| world.spawn(A(i)).id()).collect();
let entities: [Entity; 3] = entity_vec.try_into().unwrap();

world.spawn(A(73));

let mut query_state = world.query::<&A>();
let query = query_state.query(&world);

let component_values = query.get_many(entities).unwrap();

assert_eq!(component_values, [&A(0), &A(1), &A(2)]);

let wrong_entity = Entity::from_raw(365);

assert_eq!(
    match query.get_many([wrong_entity]).unwrap_err() {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);

See also

• get_many_mut to get mutable query items.
• get_many_unique to only handle unique inputs.
• many for the panicking version.

pub fn get_many_unique<const N: usize>( &self, entities: UniqueEntityEquivalentArray<Entity, N>, ) -> Result<[<<D as QueryData>::ReadOnly as QueryData>::Item<'_>; N], QueryEntityError>

Returns the read-only query items for the given UniqueEntityArray.

The returned query items are in the same order as the input. In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

Examples

use bevy_ecs::{prelude::*, query::QueryEntityError, entity::{EntitySetIterator, UniqueEntityArray, UniqueEntityVec}};

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();
let entity_set: UniqueEntityVec = world.spawn_batch((0..3).map(A)).collect_set();
let entity_set: UniqueEntityArray<3> = entity_set.try_into().unwrap();

world.spawn(A(73));

let mut query_state = world.query::<&A>();
let query = query_state.query(&world);

let component_values = query.get_many_unique(entity_set).unwrap();

assert_eq!(component_values, [&A(0), &A(1), &A(2)]);

let wrong_entity = Entity::from_raw(365);

assert_eq!(
    match query.get_many_unique(UniqueEntityArray::from([wrong_entity])).unwrap_err() {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);

See also

• get_many_unique_mut to get mutable query items.
• get_many to handle inputs with duplicates.

pub fn many<const N: usize>( &self, entities: [Entity; N], ) -> [<<D as QueryData>::ReadOnly as QueryData>::Item<'_>; N]

👎Deprecated since 0.16.0: Use get_many instead and handle the Result.

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

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 for the non-panicking version.

pub fn get_mut( &mut self, entity: Entity, ) -> Result<<D as QueryData>::Item<'_>, QueryEntityError>

Returns the query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

Example

Here, get_mut is used to retrieve the exact query item of the entity specified by the PoisonedCharacter resource.

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;
    }
}

See also

• get to get a read-only query item.

Examples found in repository

examples/picking/sprite_picking.rs (line 156)

fn recolor_on<E: Debug + Clone + Reflect>(color: Color) -> impl Fn(Trigger<E>, Query<&mut Sprite>) {
    move |ev, mut sprites| {
        let Ok(mut sprite) = sprites.get_mut(ev.target()) else {
            return;
        };
        sprite.color = color;
    }
}

examples/ecs/removal_detection.rs (line 54)

fn react_on_removal(trigger: Trigger<OnRemove, MyComponent>, mut query: Query<&mut Sprite>) {
    // The `OnRemove` trigger was automatically called on the `Entity` that had its `MyComponent` removed.
    let entity = trigger.target();
    if let Ok(mut sprite) = query.get_mut(entity) {
        sprite.color = Color::srgb(0.5, 1., 1.);
    }
}

examples/ecs/observer_propagation.rs (line 113)

fn take_damage(
    trigger: Trigger<Attack>,
    mut hp: Query<(&mut HitPoints, &Name)>,
    mut commands: Commands,
    mut app_exit: EventWriter<AppExit>,
) {
    let attack = trigger.event();
    let (mut hp, name) = hp.get_mut(trigger.target()).unwrap();
    **hp = hp.saturating_sub(attack.damage);

    if **hp > 0 {
        info!("{} has {:.1} HP", name, hp.0);
    } else {
        warn!("💀 {} has died a gruesome death", name);
        commands.entity(trigger.target()).despawn();
        app_exit.write(AppExit::Success);
    }

    info!("(propagation reached root)\n");
}

examples/picking/mesh_picking.rs (line 167)

fn update_material_on<E>(
    new_material: Handle<StandardMaterial>,
) -> impl Fn(Trigger<E>, Query<&mut MeshMaterial3d<StandardMaterial>>) {
    // An observer closure that captures `new_material`. We do this to avoid needing to write four
    // versions of this observer, each triggered by a different event and with a different hardcoded
    // material. Instead, the event type is a generic, and the material is passed in.
    move |trigger, mut query| {
        if let Ok(mut material) = query.get_mut(trigger.target()) {
            material.0 = new_material.clone();
        }
    }
}

/// A system that draws hit indicators for every pointer.
fn draw_mesh_intersections(pointers: Query<&PointerInteraction>, mut gizmos: Gizmos) {
    for (point, normal) in pointers
        .iter()
        .filter_map(|interaction| interaction.get_nearest_hit())
        .filter_map(|(_entity, hit)| hit.position.zip(hit.normal))
    {
        gizmos.sphere(point, 0.05, RED_500);
        gizmos.arrow(point, point + normal.normalize() * 0.5, PINK_100);
    }
}

/// A system that rotates all shapes.
fn rotate(mut query: Query<&mut Transform, With<Shape>>, time: Res<Time>) {
    for mut transform in &mut query {
        transform.rotate_y(time.delta_secs() / 2.);
    }
}

/// An observer to rotate an entity when it is dragged
fn rotate_on_drag(drag: Trigger<Pointer<Drag>>, mut transforms: Query<&mut Transform>) {
    let mut transform = transforms.get_mut(drag.target()).unwrap();
    transform.rotate_y(drag.delta.x * 0.02);
    transform.rotate_x(drag.delta.y * 0.02);
}

examples/ui/directional_navigation.rs (line 74)

fn universal_button_click_behavior(
    mut trigger: Trigger<Pointer<Click>>,
    mut button_query: Query<(&mut BackgroundColor, &mut ResetTimer)>,
) {
    let button_entity = trigger.target();
    if let Ok((mut color, mut reset_timer)) = button_query.get_mut(button_entity) {
        // This would be a great place to play a little sound effect too!
        color.0 = PRESSED_BUTTON.into();
        reset_timer.0 = Timer::from_seconds(0.3, TimerMode::Once);

        // Picking events propagate up the hierarchy,
        // so we need to stop the propagation here now that we've handled it
        trigger.propagate(false);
    }
}

examples/3d/update_gltf_scene.rs (line 66)

fn move_scene_entities(
    time: Res<Time>,
    moved_scene: Query<Entity, With<MovedScene>>,
    children: Query<&Children>,
    mut transforms: Query<&mut Transform>,
) {
    for moved_scene_entity in &moved_scene {
        let mut offset = 0.;
        for entity in children.iter_descendants(moved_scene_entity) {
            if let Ok(mut transform) = transforms.get_mut(entity) {
                transform.translation = Vec3::new(
                    offset * ops::sin(time.elapsed_secs()) / 20.,
                    0.,
                    ops::cos(time.elapsed_secs()) / 20.,
                );
                offset += 0.5;
            }
        }
    }
}

Additional examples can be found in:

• examples/ui/ui_texture_slice.rs
• examples/testbed/3d.rs
• examples/ui/ghost_nodes.rs
• examples/ui/ui_texture_atlas_slice.rs
• examples/3d/split_screen.rs
• examples/ui/display_and_visibility.rs
• examples/testbed/full_ui.rs
• examples/ui/button.rs
• examples/ui/tab_navigation.rs
• examples/animation/gltf_skinned_mesh.rs
• examples/ui/scroll.rs
• examples/3d/motion_blur.rs
• examples/games/contributors.rs
• examples/ecs/hierarchy.rs
• examples/3d/mixed_lighting.rs
• examples/picking/simple_picking.rs
• examples/animation/animated_mesh.rs
• examples/picking/debug_picking.rs
• examples/games/alien_cake_addict.rs
• examples/animation/easing_functions.rs
• examples/ui/size_constraints.rs

pub fn get_inner( self, entity: Entity, ) -> Result<<D as QueryData>::Item<'w>, QueryEntityError>

Returns the query item for the given Entity. This consumes the Query to return results with the actual “inner” world lifetime.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

See also

• get_mut to get the item using a mutable borrow of the Query.

pub fn get_many_mut<const N: usize>( &mut self, entities: [Entity; N], ) -> Result<[<D as QueryData>::Item<'_>; N], QueryEntityError>

Returns the query items for the given array of Entity.

The returned query items are in the same order as the input. In case of a nonexisting entity, duplicate entities or mismatched component, a QueryEntityError is returned instead.

Examples

use bevy_ecs::prelude::*;
use bevy_ecs::query::QueryEntityError;

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();

let entities: Vec<Entity> = (0..3).map(|i| world.spawn(A(i)).id()).collect();
let entities: [Entity; 3] = entities.try_into().unwrap();

world.spawn(A(73));
let wrong_entity = Entity::from_raw(57);
let invalid_entity = world.spawn_empty().id();


let mut query_state = world.query::<&mut A>();
let mut query = query_state.query_mut(&mut world);

let mut mutable_component_values = query.get_many_mut(entities).unwrap();

for mut a in &mut mutable_component_values {
    a.0 += 5;
}

let component_values = query.get_many(entities).unwrap();

assert_eq!(component_values, [&A(5), &A(6), &A(7)]);

assert_eq!(
    match query
        .get_many_mut([wrong_entity])
        .unwrap_err()
    {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);
assert_eq!(
    match query
        .get_many_mut([invalid_entity])
        .unwrap_err()
    {
        QueryEntityError::QueryDoesNotMatch(entity, _) => entity,
        _ => panic!(),
    },
    invalid_entity
);
assert_eq!(
    query
        .get_many_mut([entities[0], entities[0]])
        .unwrap_err(),
    QueryEntityError::AliasedMutability(entities[0])
);

See also

• get_many to get read-only query items without checking for duplicate entities.
• many_mut for the panicking version.

pub fn get_many_unique_mut<const N: usize>( &mut self, entities: UniqueEntityEquivalentArray<Entity, N>, ) -> Result<[<D as QueryData>::Item<'_>; N], QueryEntityError>

Returns the query items for the given UniqueEntityArray.

The returned query items are in the same order as the input. In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

Examples

use bevy_ecs::{prelude::*, query::QueryEntityError, entity::{EntitySetIterator, UniqueEntityArray, UniqueEntityVec}};

#[derive(Component, PartialEq, Debug)]
struct A(usize);

let mut world = World::new();

let entity_set: UniqueEntityVec = world.spawn_batch((0..3).map(A)).collect_set();
let entity_set: UniqueEntityArray<3> = entity_set.try_into().unwrap();

world.spawn(A(73));
let wrong_entity = Entity::from_raw(57);
let invalid_entity = world.spawn_empty().id();


let mut query_state = world.query::<&mut A>();
let mut query = query_state.query_mut(&mut world);

let mut mutable_component_values = query.get_many_unique_mut(entity_set).unwrap();

for mut a in &mut mutable_component_values {
    a.0 += 5;
}

let component_values = query.get_many_unique(entity_set).unwrap();

assert_eq!(component_values, [&A(5), &A(6), &A(7)]);

assert_eq!(
    match query
        .get_many_unique_mut(UniqueEntityArray::from([wrong_entity]))
        .unwrap_err()
    {
        QueryEntityError::EntityDoesNotExist(error) => error.entity,
        _ => panic!(),
    },
    wrong_entity
);
assert_eq!(
    match query
        .get_many_unique_mut(UniqueEntityArray::from([invalid_entity]))
        .unwrap_err()
    {
        QueryEntityError::QueryDoesNotMatch(entity, _) => entity,
        _ => panic!(),
    },
    invalid_entity
);

See also

• get_many_unique to get read-only query items.

pub fn get_many_mut_inner<const N: usize>( self, entities: [Entity; N], ) -> Result<[<D as QueryData>::Item<'w>; N], QueryEntityError>

Returns the query items for the given array of Entity. This consumes the Query to return results with the actual “inner” world lifetime.

The returned query items are in the same order as the input. In case of a nonexisting entity, duplicate entities or mismatched component, a QueryEntityError is returned instead.

See also

• get_many to get read-only query items without checking for duplicate entities.
• get_many_mut to get items using a mutable reference.
• get_many_inner to get read-only query items with the actual “inner” world lifetime.

pub fn get_many_inner<const N: usize>( self, entities: [Entity; N], ) -> Result<[<D as QueryData>::Item<'w>; N], QueryEntityError>

where D: ReadOnlyQueryData,

Returns the query items for the given array of Entity. This consumes the Query to return results with the actual “inner” world lifetime.

The returned query items are in the same order as the input. In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

See also

• get_many to get read-only query items without checking for duplicate entities.
• get_many_mut to get items using a mutable reference.
• get_many_mut_inner to get mutable query items with the actual “inner” world lifetime.

pub fn get_many_unique_inner<const N: usize>( self, entities: UniqueEntityEquivalentArray<Entity, N>, ) -> Result<[<D as QueryData>::Item<'w>; N], QueryEntityError>

Returns the query items for the given UniqueEntityArray. This consumes the Query to return results with the actual “inner” world lifetime.

The returned query items are in the same order as the input. In case of a nonexisting entity, duplicate entities or mismatched component, a QueryEntityError is returned instead.

See also

• get_many_unique to get read-only query items without checking for duplicate entities.
• get_many_unique_mut to get items using a mutable reference.

pub fn many_mut<const N: usize>( &mut self, entities: [Entity; N], ) -> [<D as QueryData>::Item<'_>; N]

👎Deprecated since 0.16.0: Use get_many_mut instead and handle the Result.

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

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);

         // Silence borrow-checker: I have split your mutable borrow!
         force_2.x += spring.strength * (position_2.x - position_1.x);
         force_2.y += spring.strength * (position_2.y - position_1.y);
    }
}

See also

• get_many_mut for the non panicking version.
• many to get read-only query items.

pub unsafe fn get_unchecked( &self, entity: Entity, ) -> Result<<D as QueryData>::Item<'_>, QueryEntityError>

Returns the query item for the given Entity.

In case of a nonexisting entity or mismatched component, a QueryEntityError is returned instead.

This is always guaranteed to run in O(1) time.

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

• get_mut for the safe version.

pub fn single( &self, ) -> Result<<<D as QueryData>::ReadOnly as QueryData>::Item<'_>, QuerySingleError>

Returns a single read-only query item when there is exactly one entity matching the query.

If the number of query items is not exactly one, a QuerySingleError is returned instead.

Example

fn player_scoring_system(query: Query<&PlayerScore>) {
    match query.single() {
        Ok(PlayerScore(score)) => {
            println!("Score: {}", score);
        }
        Err(QuerySingleError::NoEntities(_)) => {
            println!("Error: There is no player!");
        }
        Err(QuerySingleError::MultipleEntities(_)) => {
            println!("Error: There is more than one player!");
        }
    }
}

See also

• single_mut to get the mutable query item.

Examples found in repository

examples/audio/audio_control.rs (line 38)

fn update_speed(music_controller: Query<&AudioSink, With<MyMusic>>, time: Res<Time>) {
    let Ok(sink) = music_controller.single() else {
        return;
    };

    sink.set_speed((ops::sin(time.elapsed_secs() / 5.0) + 1.0).max(0.1));
}

fn pause(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    music_controller: Query<&AudioSink, With<MyMusic>>,
) {
    let Ok(sink) = music_controller.single() else {
        return;
    };

    if keyboard_input.just_pressed(KeyCode::Space) {
        sink.toggle_playback();
    }
}

examples/ecs/observers.rs (line 178)

fn handle_click(
    mouse_button_input: Res<ButtonInput<MouseButton>>,
    camera: Single<(&Camera, &GlobalTransform)>,
    windows: Query<&Window>,
    mut commands: Commands,
) {
    let Ok(windows) = windows.single() else {
        return;
    };

    let (camera, camera_transform) = *camera;
    if let Some(pos) = windows
        .cursor_position()
        .and_then(|cursor| camera.viewport_to_world(camera_transform, cursor).ok())
        .map(|ray| ray.origin.truncate())
    {
        if mouse_button_input.just_pressed(MouseButton::Left) {
            commands.trigger(ExplodeMines { pos, radius: 1.0 });
        }
    }
}

examples/3d/tonemapping.rs (line 215)

fn drag_drop_image(
    image_mat: Query<&MeshMaterial3d<StandardMaterial>, With<HDRViewer>>,
    text: Query<Entity, (With<Text>, With<SceneNumber>)>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    mut drop_events: EventReader<FileDragAndDrop>,
    asset_server: Res<AssetServer>,
    mut commands: Commands,
) {
    let Some(new_image) = drop_events.read().find_map(|e| match e {
        FileDragAndDrop::DroppedFile { path_buf, .. } => {
            Some(asset_server.load(path_buf.to_string_lossy().to_string()))
        }
        _ => None,
    }) else {
        return;
    };

    for mat_h in &image_mat {
        if let Some(mat) = materials.get_mut(mat_h) {
            mat.base_color_texture = Some(new_image.clone());

            // Despawn the image viewer instructions
            if let Ok(text_entity) = text.single() {
                commands.entity(text_entity).despawn();
            }
        }
    }
}

examples/window/window_drag_move.rs (line 103)

fn handle_input(
    input: Res<ButtonInput<KeyCode>>,
    mut action: ResMut<LeftClickAction>,
    mut dir: ResMut<ResizeDir>,
    example_text: Query<Entity, With<Text>>,
    mut writer: TextUiWriter,
) -> Result {
    use LeftClickAction::*;
    if input.just_pressed(KeyCode::KeyA) {
        *action = match *action {
            Move => Resize,
            Resize => Nothing,
            Nothing => Move,
        };
        *writer.text(example_text.single()?, 4) = format!("{:?}", *action);
    }

    if input.just_pressed(KeyCode::KeyS) {
        dir.0 = dir
            .0
            .checked_sub(1)
            .unwrap_or(DIRECTIONS.len().saturating_sub(1));
        *writer.text(example_text.single()?, 7) = format!("{:?}", DIRECTIONS[dir.0]);
    }

    if input.just_pressed(KeyCode::KeyD) {
        dir.0 = (dir.0 + 1) % DIRECTIONS.len();
        *writer.text(example_text.single()?, 7) = format!("{:?}", DIRECTIONS[dir.0]);
    }

    Ok(())
}

examples/2d/2d_viewport_to_world.rs (line 31)

fn draw_cursor(
    camera_query: Single<(&Camera, &GlobalTransform)>,
    window: Query<&Window>,
    mut gizmos: Gizmos,
) {
    let (camera, camera_transform) = *camera_query;
    let Ok(window) = window.single() else {
        return;
    };

    let Some(cursor_position) = window.cursor_position() else {
        return;
    };

    // Calculate a world position based on the cursor's position.
    let Ok(world_pos) = camera.viewport_to_world_2d(camera_transform, cursor_position) else {
        return;
    };

    // To test Camera::world_to_viewport, convert result back to viewport space and then back to world space.
    let Ok(viewport_check) = camera.world_to_viewport(camera_transform, world_pos.extend(0.0))
    else {
        return;
    };
    let Ok(world_check) = camera.viewport_to_world_2d(camera_transform, viewport_check.xy()) else {
        return;
    };

    gizmos.circle_2d(world_pos, 10., WHITE);
    // Should be the same as world_pos
    gizmos.circle_2d(world_check, 8., RED);
}

fn controls(
    mut camera_query: Query<(&mut Camera, &mut Transform, &mut Projection)>,
    window: Query<&Window>,
    input: Res<ButtonInput<KeyCode>>,
    time: Res<Time<Fixed>>,
) {
    let Ok(window) = window.single() else {
        return;
    };
    let Ok((mut camera, mut transform, mut projection)) = camera_query.single_mut() else {
        return;
    };
    let fspeed = 600.0 * time.delta_secs();
    let uspeed = fspeed as u32;
    let window_size = window.resolution.physical_size();

    // Camera movement controls
    if input.pressed(KeyCode::ArrowUp) {
        transform.translation.y += fspeed;
    }
    if input.pressed(KeyCode::ArrowDown) {
        transform.translation.y -= fspeed;
    }
    if input.pressed(KeyCode::ArrowLeft) {
        transform.translation.x -= fspeed;
    }
    if input.pressed(KeyCode::ArrowRight) {
        transform.translation.x += fspeed;
    }

    // Camera zoom controls
    if let Projection::Orthographic(projection2d) = &mut *projection {
        if input.pressed(KeyCode::Comma) {
            projection2d.scale *= powf(4.0f32, time.delta_secs());
        }

        if input.pressed(KeyCode::Period) {
            projection2d.scale *= powf(0.25f32, time.delta_secs());
        }
    }

    if let Some(viewport) = camera.viewport.as_mut() {
        // Viewport movement controls
        if input.pressed(KeyCode::KeyW) {
            viewport.physical_position.y = viewport.physical_position.y.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyS) {
            viewport.physical_position.y += uspeed;
        }
        if input.pressed(KeyCode::KeyA) {
            viewport.physical_position.x = viewport.physical_position.x.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyD) {
            viewport.physical_position.x += uspeed;
        }

        // Bound viewport position so it doesn't go off-screen
        viewport.physical_position = viewport
            .physical_position
            .min(window_size - viewport.physical_size);

        // Viewport size controls
        if input.pressed(KeyCode::KeyI) {
            viewport.physical_size.y = viewport.physical_size.y.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyK) {
            viewport.physical_size.y += uspeed;
        }
        if input.pressed(KeyCode::KeyJ) {
            viewport.physical_size.x = viewport.physical_size.x.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyL) {
            viewport.physical_size.x += uspeed;
        }

        // Bound viewport size so it doesn't go off-screen
        viewport.physical_size = viewport
            .physical_size
            .min(window_size - viewport.physical_position)
            .max(UVec2::new(20, 20));
    }
}

examples/ecs/parallel_query.rs (line 46)

fn bounce_system(window: Query<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
    let Ok(window) = window.single() else {
        return;
    };
    let width = window.width();
    let height = window.height();
    let left = width / -2.0;
    let right = width / 2.0;
    let bottom = height / -2.0;
    let top = height / 2.0;
    // The default batch size can also be overridden.
    // In this case a batch size of 32 is chosen to limit the overhead of
    // ParallelIterator, since negating a vector is very inexpensive.
    sprites
        .par_iter_mut()
        .batching_strategy(BatchingStrategy::fixed(32))
        .for_each(|(transform, mut v)| {
            if !(left < transform.translation.x
                && transform.translation.x < right
                && bottom < transform.translation.y
                && transform.translation.y < top)
            {
                // For simplicity, just reverse the velocity; don't use realistic bounces
                v.0 = -v.0;
            }
        });
}

Additional examples can be found in:

• examples/3d/generate_custom_mesh.rs
• examples/3d/3d_viewport_to_world.rs
• examples/stress_tests/bevymark.rs
• examples/games/contributors.rs
• examples/stress_tests/many_cameras_lights.rs

pub fn get_single( &self, ) -> Result<<<D as QueryData>::ReadOnly as QueryData>::Item<'_>, QuerySingleError>

👎Deprecated since 0.16.0: Please use single instead

A deprecated alias for single.

pub fn single_mut( &mut self, ) -> Result<<D as QueryData>::Item<'_>, QuerySingleError>

Returns a single query item when there is exactly one entity matching the query.

If the number of query items is not exactly one, a QuerySingleError is returned instead.

Example

fn regenerate_player_health_system(mut query: Query<&mut Health, With<Player>>) {
    let mut health = query.single_mut().expect("Error: Could not find a single player.");
    health.0 += 1;
}

See also

• single to get the read-only query item.

Examples found in repository

examples/audio/audio_control.rs (line 62)

fn mute(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    mut music_controller: Query<&mut AudioSink, With<MyMusic>>,
) {
    let Ok(mut sink) = music_controller.single_mut() else {
        return;
    };

    if keyboard_input.just_pressed(KeyCode::KeyM) {
        sink.toggle_mute();
    }
}

fn volume(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    mut music_controller: Query<&mut AudioSink, With<MyMusic>>,
) {
    let Ok(mut sink) = music_controller.single_mut() else {
        return;
    };

    if keyboard_input.just_pressed(KeyCode::Equal) {
        let current_volume = sink.volume();
        sink.set_volume(current_volume + Volume::Linear(0.1));
    } else if keyboard_input.just_pressed(KeyCode::Minus) {
        let current_volume = sink.volume();
        sink.set_volume(current_volume - Volume::Linear(0.1));
    }
}

examples/stress_tests/many_text2d.rs (line 158)

fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
    let Ok(mut camera_transform) = camera_query.single_mut() else {
        return;
    };
    camera_transform.rotate_z(time.delta_secs() * 0.5);
    *camera_transform =
        *camera_transform * Transform::from_translation(Vec3::X * CAMERA_SPEED * time.delta_secs());
}

examples/asset/multi_asset_sync.rs (line 261)

fn get_async_loading_state(
    state: Res<AsyncLoadingState>,
    mut next_loading_state: ResMut<NextState<LoadingState>>,
    mut text: Query<&mut Text, With<LoadingText>>,
) {
    // Load the value written by the `Future`.
    let is_loaded = state.0.load(Ordering::Acquire);

    // If loaded, change the state.
    if is_loaded {
        next_loading_state.set(LoadingState::Loaded);
        if let Ok(mut text) = text.single_mut() {
            "Loaded!".clone_into(&mut **text);
        }
    }
}

examples/ecs/entity_disabling.rs (line 72)

fn list_all_named_entities(
    query: Query<&Name>,
    mut name_text_query: Query<&mut Text, With<EntityNameText>>,
    mut commands: Commands,
) {
    let mut text_string = String::from("Named entities found:\n");
    // Query iteration order is not guaranteed, so we sort the names
    // to ensure the output is consistent.
    for name in query.iter().sort::<&Name>() {
        text_string.push_str(&format!("{:?}\n", name));
    }

    if let Ok(mut text) = name_text_query.single_mut() {
        *text = Text::new(text_string);
    } else {
        commands.spawn((
            EntityNameText,
            Text::default(),
            Node {
                position_type: PositionType::Absolute,
                top: Val::Px(12.0),
                right: Val::Px(12.0),
                ..default()
            },
        ));
    }
}

examples/camera/2d_screen_shake.rs (line 168)

fn screen_shake(
    time: Res<Time>,
    mut screen_shake: ResMut<ScreenShake>,
    mut query: Query<(&mut Camera, &mut Transform)>,
) {
    let mut rng = ChaCha8Rng::from_entropy();
    let shake = screen_shake.trauma * screen_shake.trauma;
    let angle = (screen_shake.max_angle * shake).to_radians() * rng.gen_range(-1.0..1.0);
    let offset_x = screen_shake.max_offset * shake * rng.gen_range(-1.0..1.0);
    let offset_y = screen_shake.max_offset * shake * rng.gen_range(-1.0..1.0);

    if shake > 0.0 {
        for (mut camera, mut transform) in query.iter_mut() {
            // Position
            let sub_view = camera.sub_camera_view.as_mut().unwrap();
            let target = sub_view.offset
                + Vec2 {
                    x: offset_x,
                    y: offset_y,
                };
            sub_view
                .offset
                .smooth_nudge(&target, CAMERA_DECAY_RATE, time.delta_secs());

            // Rotation
            let rotation = Quat::from_rotation_z(angle);
            transform.rotation = transform
                .rotation
                .interpolate_stable(&(transform.rotation.mul_quat(rotation)), CAMERA_DECAY_RATE);
        }
    } else {
        // return camera to the latest position of player (it's fixed in this example case)
        if let Ok((mut camera, mut transform)) = query.single_mut() {
            let sub_view = camera.sub_camera_view.as_mut().unwrap();
            let target = screen_shake.latest_position.unwrap();
            sub_view
                .offset
                .smooth_nudge(&target, 1.0, time.delta_secs());
            transform.rotation = transform.rotation.interpolate_stable(&Quat::IDENTITY, 0.1);
        }
    }
    // Decay the trauma over time
    screen_shake.trauma -= TRAUMA_DECAY_SPEED * time.delta_secs();
    screen_shake.trauma = screen_shake.trauma.clamp(0.0, 1.0);
}

examples/2d/2d_viewport_to_world.rs (line 67)

fn controls(
    mut camera_query: Query<(&mut Camera, &mut Transform, &mut Projection)>,
    window: Query<&Window>,
    input: Res<ButtonInput<KeyCode>>,
    time: Res<Time<Fixed>>,
) {
    let Ok(window) = window.single() else {
        return;
    };
    let Ok((mut camera, mut transform, mut projection)) = camera_query.single_mut() else {
        return;
    };
    let fspeed = 600.0 * time.delta_secs();
    let uspeed = fspeed as u32;
    let window_size = window.resolution.physical_size();

    // Camera movement controls
    if input.pressed(KeyCode::ArrowUp) {
        transform.translation.y += fspeed;
    }
    if input.pressed(KeyCode::ArrowDown) {
        transform.translation.y -= fspeed;
    }
    if input.pressed(KeyCode::ArrowLeft) {
        transform.translation.x -= fspeed;
    }
    if input.pressed(KeyCode::ArrowRight) {
        transform.translation.x += fspeed;
    }

    // Camera zoom controls
    if let Projection::Orthographic(projection2d) = &mut *projection {
        if input.pressed(KeyCode::Comma) {
            projection2d.scale *= powf(4.0f32, time.delta_secs());
        }

        if input.pressed(KeyCode::Period) {
            projection2d.scale *= powf(0.25f32, time.delta_secs());
        }
    }

    if let Some(viewport) = camera.viewport.as_mut() {
        // Viewport movement controls
        if input.pressed(KeyCode::KeyW) {
            viewport.physical_position.y = viewport.physical_position.y.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyS) {
            viewport.physical_position.y += uspeed;
        }
        if input.pressed(KeyCode::KeyA) {
            viewport.physical_position.x = viewport.physical_position.x.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyD) {
            viewport.physical_position.x += uspeed;
        }

        // Bound viewport position so it doesn't go off-screen
        viewport.physical_position = viewport
            .physical_position
            .min(window_size - viewport.physical_size);

        // Viewport size controls
        if input.pressed(KeyCode::KeyI) {
            viewport.physical_size.y = viewport.physical_size.y.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyK) {
            viewport.physical_size.y += uspeed;
        }
        if input.pressed(KeyCode::KeyJ) {
            viewport.physical_size.x = viewport.physical_size.x.saturating_sub(uspeed);
        }
        if input.pressed(KeyCode::KeyL) {
            viewport.physical_size.x += uspeed;
        }

        // Bound viewport size so it doesn't go off-screen
        viewport.physical_size = viewport
            .physical_size
            .min(window_size - viewport.physical_position)
            .max(UVec2::new(20, 20));
    }
}

Additional examples can be found in:

• examples/3d/../helpers/camera_controller.rs

pub fn get_single_mut( &mut self, ) -> Result<<D as QueryData>::Item<'_>, QuerySingleError>

👎Deprecated since 0.16.0: Please use single_mut instead

A deprecated alias for single_mut.

pub fn single_inner( self, ) -> Result<<D as QueryData>::Item<'w>, QuerySingleError>

Returns a single query item when there is exactly one entity matching the query. This consumes the Query to return results with the actual “inner” world lifetime.

If the number of query items is not exactly one, a QuerySingleError is returned instead.

Example

fn regenerate_player_health_system(query: Query<&mut Health, With<Player>>) {
    let mut health = query.single_inner().expect("Error: Could not find a single player.");
    health.0 += 1;
}

See also

• single to get the read-only query item.
• single_mut to get the mutable query item.
• single_inner for the panicking version.

pub fn is_empty(&self) -> bool

Returns true if there are no query items.

This is equivalent to self.iter().next().is_none(), and thus the worst case runtime will be O(n) where n is the number of potential matches. This can be notably expensive for queries that rely on non-archetypal filters such as Added or Changed which must individually check each query result for a match.

Example

Here, the score is increased only if an entity with a Player component is present in the world:

fn update_score_system(query: Query<(), With<Player>>, mut score: ResMut<Score>) {
    if !query.is_empty() {
        score.0 += 1;
    }
}

Examples found in repository

examples/3d/irradiance_volumes.rs (line 536)

fn create_cubes(
    image_assets: Res<Assets<Image>>,
    mut commands: Commands,
    irradiance_volumes: Query<(&IrradianceVolume, &GlobalTransform)>,
    voxel_cube_parents: Query<Entity, With<VoxelCubeParent>>,
    voxel_cubes: Query<Entity, With<VoxelCube>>,
    example_assets: Res<ExampleAssets>,
    mut voxel_visualization_material_assets: ResMut<Assets<VoxelVisualizationMaterial>>,
) {
    // If voxel cubes have already been spawned, don't do anything.
    if !voxel_cubes.is_empty() {
        return;
    }

    let Some(voxel_cube_parent) = voxel_cube_parents.iter().next() else {
        return;
    };

    for (irradiance_volume, global_transform) in irradiance_volumes.iter() {
        let Some(image) = image_assets.get(&irradiance_volume.voxels) else {
            continue;
        };

        let resolution = image.texture_descriptor.size;

        let voxel_cube_material = voxel_visualization_material_assets.add(ExtendedMaterial {
            base: StandardMaterial::from(Color::from(RED)),
            extension: VoxelVisualizationExtension {
                irradiance_volume_info: VoxelVisualizationIrradianceVolumeInfo {
                    world_from_voxel: VOXEL_FROM_WORLD.inverse(),
                    voxel_from_world: VOXEL_FROM_WORLD,
                    resolution: uvec3(
                        resolution.width,
                        resolution.height,
                        resolution.depth_or_array_layers,
                    ),
                    intensity: IRRADIANCE_VOLUME_INTENSITY,
                },
            },
        });

        let scale = vec3(
            1.0 / resolution.width as f32,
            1.0 / resolution.height as f32,
            1.0 / resolution.depth_or_array_layers as f32,
        );

        // Spawn a cube for each voxel.
        for z in 0..resolution.depth_or_array_layers {
            for y in 0..resolution.height {
                for x in 0..resolution.width {
                    let uvw = (uvec3(x, y, z).as_vec3() + 0.5) * scale - 0.5;
                    let pos = global_transform.transform_point(uvw);
                    let voxel_cube = commands
                        .spawn((
                            Mesh3d(example_assets.voxel_cube.clone()),
                            MeshMaterial3d(voxel_cube_material.clone()),
                            Transform::from_scale(Vec3::splat(VOXEL_CUBE_SCALE))
                                .with_translation(pos),
                        ))
                        .insert(VoxelCube)
                        .insert(NotShadowCaster)
                        .id();

                    commands.entity(voxel_cube_parent).add_child(voxel_cube);
                }
            }
        }
    }
}

pub fn contains(&self, entity: Entity) -> bool

Returns true if the given Entity matches the query.

This is always guaranteed to run in O(1) time.

Example

fn targeting_system(in_range_query: Query<&InRange>, target: Res<Target>) {
    if in_range_query.contains(target.entity) {
        println!("Bam!")
    }
}

Examples found in repository

examples/ecs/entity_disabling.rs (line 47)

fn disable_entities_on_click(
    trigger: Trigger<Pointer<Click>>,
    valid_query: Query<&DisableOnClick>,
    mut commands: Commands,
) {
    let clicked_entity = trigger.target();
    // Windows and text are entities and can be clicked!
    // We definitely don't want to disable the window itself,
    // because that would cause the app to close!
    if valid_query.contains(clicked_entity) {
        // Just add the `Disabled` component to the entity to disable it.
        // Note that the `Disabled` component is *only* added to the entity,
        // its children are not affected.
        commands.entity(clicked_entity).insert(Disabled);
    }
}

pub fn transmute_lens<NewD>(&mut self) -> QueryLens<'_, NewD>

where NewD: QueryData,

Returns a QueryLens that can be used to get a query with a more general fetch.

For example, this can transform a Query<(&A, &mut B)> to a Query<&B>. This can be useful for passing the query to another function. Note that since filter terms are dropped, non-archetypal filters like Added and Changed will not be respected. To maintain or change filter terms see Self::transmute_lens_filtered

Panics

This will panic if NewD is not a subset of the original fetch D

Example

fn reusable_function(lens: &mut QueryLens<&A>) {
    assert_eq!(lens.query().single().unwrap().0, 10);
}

// We can use the function in a system that takes the exact query.
fn system_1(mut query: Query<&A>) {
    reusable_function(&mut query.as_query_lens());
}

// We can also use it with a query that does not match exactly
// by transmuting it.
fn system_2(mut query: Query<(&mut A, &B)>) {
    let mut lens = query.transmute_lens::<&A>();
    reusable_function(&mut lens);
}

Allowed Transmutes

Besides removing parameters from the query, you can also make limited changes to the types of parameters. The new query must have a subset of the read, write, and required access of the original query.

• &mut T and Mut<T> have read, write, and required access to T
• &T and Ref<T> have read and required access to T
• Option<D> and AnyOf<(D, ...)> have the read and write access of the subqueries, but no required access
• Tuples of query data and #[derive(QueryData)] structs have the union of the access of their subqueries
• EntityMut has read and write access to all components, but no required access
• EntityRef has read access to all components, but no required access
• Entity, EntityLocation, &Archetype, Has<T>, and PhantomData<T> have no access at all, so can be added to any query
• FilteredEntityRef and FilteredEntityMut have access determined by the QueryBuilder used to construct them. Any query can be transmuted to them, and they will receive the access of the source query, but only if they are the top-level query and not nested
• Added<T> and Changed<T> filters have read and required access to T
• With<T> and Without<T> filters have no access at all, so can be added to any query
• Tuples of query filters and #[derive(QueryFilter)] structs have the union of the access of their subqueries
• Or<(F, ...)> filters have the read access of the subqueries, but no required access

Examples of valid transmutes

// `&mut T` and `Mut<T>` access the same data and can be transmuted to each other,
// `&T` and `Ref<T>` access the same data and can be transmuted to each other,
// and mutable versions can be transmuted to read-only versions
assert_valid_transmute::<&mut T, &T>();
assert_valid_transmute::<&mut T, Mut<T>>();
assert_valid_transmute::<Mut<T>, &mut T>();
assert_valid_transmute::<&T, Ref<T>>();
assert_valid_transmute::<Ref<T>, &T>();

// The structure can be rearranged, or subqueries dropped
assert_valid_transmute::<(&T, &U), &T>();
assert_valid_transmute::<((&T, &U), &V), (&T, (&U, &V))>();
assert_valid_transmute::<Option<(&T, &U)>, (Option<&T>, Option<&U>)>();

// Queries with no access can be freely added
assert_valid_transmute::<
    &T,
    (&T, Entity, EntityLocation, &Archetype, Has<U>, PhantomData<T>),
>();

// Required access can be transmuted to optional,
// and optional access can be transmuted to other optional access
assert_valid_transmute::<&T, Option<&T>>();
assert_valid_transmute::<AnyOf<(&mut T, &mut U)>, Option<&T>>();
// Note that removing subqueries from `AnyOf` will result
// in an `AnyOf` where all subqueries can yield `None`!
assert_valid_transmute::<AnyOf<(&T, &U, &V)>, AnyOf<(&T, &U)>>();
assert_valid_transmute::<EntityMut, Option<&mut T>>();

// Anything can be transmuted to `FilteredEntityRef` or `FilteredEntityMut`
// This will create a `FilteredEntityMut` that only has read access to `T`
assert_valid_transmute::<&T, FilteredEntityMut>();
// This transmute will succeed, but the `FilteredEntityMut` will have no access!
// It must be the top-level query to be given access, but here it is nested in a tuple.
assert_valid_transmute::<&T, (Entity, FilteredEntityMut)>();

// `Added<T>` and `Changed<T>` filters have the same access as `&T` data
// Remember that they are only evaluated on the transmuted query, not the original query!
assert_valid_transmute_filtered::<Entity, Changed<T>, &T, ()>();
assert_valid_transmute_filtered::<&mut T, (), &T, Added<T>>();
// Nested inside of an `Or` filter, they have the same access as `Option<&T>`.
assert_valid_transmute_filtered::<Option<&T>, (), Entity, Or<(Changed<T>, With<U>)>>();

pub fn transmute_lens_inner<NewD>(self) -> QueryLens<'w, NewD>

where NewD: QueryData,

Returns a QueryLens that can be used to get a query with a more general fetch. This consumes the Query to return results with the actual “inner” world lifetime.

For example, this can transform a Query<(&A, &mut B)> to a Query<&B>. This can be useful for passing the query to another function. Note that since filter terms are dropped, non-archetypal filters like Added and Changed will not be respected. To maintain or change filter terms see Self::transmute_lens_filtered

Panics

This will panic if NewD is not a subset of the original fetch Q

Example

fn reusable_function(mut lens: QueryLens<&A>) {
    assert_eq!(lens.query().single().unwrap().0, 10);
}

// We can use the function in a system that takes the exact query.
fn system_1(query: Query<&A>) {
    reusable_function(query.into_query_lens());
}

// We can also use it with a query that does not match exactly
// by transmuting it.
fn system_2(query: Query<(&mut A, &B)>) {
    let mut lens = query.transmute_lens_inner::<&A>();
    reusable_function(lens);
}

Allowed Transmutes

Besides removing parameters from the query, you can also make limited changes to the types of parameters.

• Can always add/remove Entity
• Can always add/remove EntityLocation
• Can always add/remove &Archetype
• Ref<T> <-> &T
• &mut T -> &T
• &mut T -> Ref<T>
• EntityMut -> EntityRef

See also

• transmute_lens to convert to a lens using a mutable borrow of the Query.

pub fn transmute_lens_filtered<NewD, NewF>( &mut self, ) -> QueryLens<'_, NewD, NewF>

where NewD: QueryData, NewF: QueryFilter,

Equivalent to Self::transmute_lens but also includes a QueryFilter type.

Note that the lens will iterate the same tables and archetypes as the original query. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added and Changed will only be respected if they are in the type signature.

pub fn transmute_lens_filtered_inner<NewD, NewF>( self, ) -> QueryLens<'w, NewD, NewF>

where NewD: QueryData, NewF: QueryFilter,

Equivalent to Self::transmute_lens_inner but also includes a QueryFilter type. This consumes the Query to return results with the actual “inner” world lifetime.

Note that the lens will iterate the same tables and archetypes as the original query. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added and Changed will only be respected if they are in the type signature.

See also

• transmute_lens_filtered to convert to a lens using a mutable borrow of the Query.

pub fn as_query_lens(&mut self) -> QueryLens<'_, D>

Gets a QueryLens with the same accesses as the existing query

pub fn into_query_lens(self) -> QueryLens<'w, D>

Gets a QueryLens with the same accesses as the existing query

See also

• as_query_lens to convert to a lens using a mutable borrow of the Query.

pub fn join<'a, OtherD, NewD>( &'a mut self, other: &'a mut Query<'_, '_, OtherD>, ) -> QueryLens<'a, NewD>

where OtherD: QueryData, NewD: QueryData,

Returns a QueryLens that can be used to get a query with the combined fetch.

For example, this can take a Query<&A> and a Query<&B> and return a Query<(&A, &B)>. The returned query will only return items with both A and B. Note that since filters are dropped, non-archetypal filters like Added and Changed will not be respected. To maintain or change filter terms see Self::join_filtered.

Example

fn system(
    mut transforms: Query<&Transform>,
    mut players: Query<&Player>,
    mut enemies: Query<&Enemy>
) {
    let mut players_transforms: QueryLens<(&Transform, &Player)> = transforms.join(&mut players);
    for (transform, player) in &players_transforms.query() {
        // do something with a and b
    }

    let mut enemies_transforms: QueryLens<(&Transform, &Enemy)> = transforms.join(&mut enemies);
    for (transform, enemy) in &enemies_transforms.query() {
        // do something with a and b
    }
}

Panics

This will panic if NewD is not a subset of the union of the original fetch Q and OtherD.

Allowed Transmutes

Like transmute_lens the query terms can be changed with some restrictions. See Self::transmute_lens for more details.

pub fn join_inner<OtherD, NewD>( self, other: Query<'w, '_, OtherD>, ) -> QueryLens<'w, NewD>

where OtherD: QueryData, NewD: QueryData,

Returns a QueryLens that can be used to get a query with the combined fetch. This consumes the Query to return results with the actual “inner” world lifetime.

For example, this can take a Query<&A> and a Query<&B> and return a Query<(&A, &B)>. The returned query will only return items with both A and B. Note that since filters are dropped, non-archetypal filters like Added and Changed will not be respected. To maintain or change filter terms see Self::join_filtered.

Panics

This will panic if NewD is not a subset of the union of the original fetch Q and OtherD.

Allowed Transmutes

Like transmute_lens the query terms can be changed with some restrictions. See Self::transmute_lens for more details.

See also

• join to join using a mutable borrow of the Query.

pub fn join_filtered<'a, OtherD, OtherF, NewD, NewF>( &'a mut self, other: &'a mut Query<'_, '_, OtherD, OtherF>, ) -> QueryLens<'a, NewD, NewF>

where OtherD: QueryData, OtherF: QueryFilter, NewD: QueryData, NewF: QueryFilter,

Equivalent to Self::join but also includes a QueryFilter type.

Note that the lens with iterate a subset of the original queries’ tables and archetypes. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added and Changed will only be respected if they are in the type signature.

pub fn join_filtered_inner<OtherD, OtherF, NewD, NewF>( self, other: Query<'w, '_, OtherD, OtherF>, ) -> QueryLens<'w, NewD, NewF>

where OtherD: QueryData, OtherF: QueryFilter, NewD: QueryData, NewF: QueryFilter,

Equivalent to Self::join_inner but also includes a QueryFilter type. This consumes the Query to return results with the actual “inner” world lifetime.

Note that the lens with iterate a subset of the original queries’ tables and archetypes. This means that additional archetypal query terms like With and Without will not necessarily be respected and non-archetypal terms like Added and Changed will only be respected if they are in the type signature.

See also

• join_filtered to join using a mutable borrow of the Query.

impl<'w, 's, D, F> Query<'w, 's, D, F>

where D: ReadOnlyQueryData, F: QueryFilter,

pub fn iter_inner(&self) -> QueryIter<'w, 's, <D as QueryData>::ReadOnly, F>

Returns an Iterator over the query items, with the actual “inner” world lifetime.

This can only return immutable data (mutable data will be cast to an immutable form). See Self::iter_mut for queries that contain at least one mutable component.

Example

Here, the report_names_system iterates over the Player component of every entity that contains it:

fn report_names_system(query: Query<&Player>) {
    for player in &query {
        println!("Say hello to {}!", player.name);
    }
}

Trait Implementations

impl<D, F> Clone for Query<'_, '_, D, F>

where D: ReadOnlyQueryData, F: QueryFilter,

fn clone(&self) -> Query<'_, '_, D, F>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<D, F> Debug for Query<'_, '_, D, F>

where D: QueryData, F: QueryFilter,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<'w, 'q, Q, F> From<&'q mut Query<'w, '_, Q, F>> for QueryLens<'q, Q, F>

where Q: QueryData, F: QueryFilter,

fn from(value: &'q mut Query<'w, '_, Q, F>) -> QueryLens<'q, Q, F>

Converts to this type from the input type.

impl<'w, 's, Q, F> From<&'s mut QueryLens<'w, Q, F>> for Query<'s, 's, Q, F>

where Q: QueryData, F: QueryFilter,

fn from(value: &'s mut QueryLens<'w, Q, F>) -> Query<'s, 's, Q, F>

Converts to this type from the input type.

impl<'w, 's, D, F> IntoIterator for &'w Query<'_, 's, D, F>

where D: QueryData, F: QueryFilter,

type Item = <<D as QueryData>::ReadOnly as QueryData>::Item<'w>

The type of the elements being iterated over.

type IntoIter = QueryIter<'w, 's, <D as QueryData>::ReadOnly, F>

Which kind of iterator are we turning this into?

fn into_iter(self) -> <&'w Query<'_, 's, D, F> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'w, 's, D, F> IntoIterator for &'w mut Query<'_, 's, D, F>

where D: QueryData, F: QueryFilter,

type Item = <D as QueryData>::Item<'w>

The type of the elements being iterated over.

type IntoIter = QueryIter<'w, 's, D, F>

Which kind of iterator are we turning this into?

fn into_iter(self) -> <&'w mut Query<'_, 's, D, F> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<'w, 's, D, F> IntoIterator for Query<'w, 's, D, F>

where D: QueryData, F: QueryFilter,

type Item = <D as QueryData>::Item<'w>

The type of the elements being iterated over.

type IntoIter = QueryIter<'w, 's, D, F>

Which kind of iterator are we turning this into?

fn into_iter(self) -> <Query<'w, 's, D, F> as IntoIterator>::IntoIter

Creates an iterator from a value.

impl<D, F> SystemParam for Query<'_, '_, D, F>

where D: QueryData + 'static, F: QueryFilter + 'static,

type State = QueryState<D, F>

Used to store data which persists across invocations of a system.

type Item<'w, 's> = Query<'w, 's, D, F>

The item type returned when constructing this system param. The value of this associated type should be Self, instantiated with new lifetimes.

fn init_state( world: &mut World, system_meta: &mut SystemMeta, ) -> <Query<'_, '_, D, F> as SystemParam>::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

unsafe fn new_archetype( state: &mut <Query<'_, '_, D, F> as SystemParam>::State, archetype: &Archetype, system_meta: &mut SystemMeta, )

For the specified Archetype, registers the components accessed by this SystemParam (if applicable).a

unsafe fn get_param<'w, 's>( state: &'s mut <Query<'_, '_, D, F> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'w>, change_tick: Tick, ) -> <Query<'_, '_, D, F> as SystemParam>::Item<'w, 's>

Creates a parameter to be passed into a SystemParamFunction.

fn apply(state: &mut Self::State, system_meta: &SystemMeta, world: &mut World)

Applies any deferred mutations stored in this SystemParam’s state. This is used to apply Commands during ApplyDeferred.

fn queue( state: &mut Self::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )

Queues any deferred mutations to be applied at the next ApplyDeferred.

unsafe fn validate_param( state: &Self::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'_>, ) -> Result<(), SystemParamValidationError>

Validates that the param can be acquired by the get_param.

impl<'w, 's, D, F, T> SystemParamBuilder<Query<'w, 's, D, F>> for QueryParamBuilder<T>

where D: QueryData + 'static, F: QueryFilter + 'static, T: FnOnce(&mut QueryBuilder<'_, D, F>),

fn build( self, world: &mut World, system_meta: &mut SystemMeta, ) -> QueryState<D, F>

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

fn build_state(self, world: &mut World) -> SystemState<P>

Create a SystemState from a SystemParamBuilder. To create a system, call SystemState::build_system on the result.

impl<'w, 's, D, F> SystemParamBuilder<Query<'w, 's, D, F>> for QueryState<D, F>

where D: QueryData + 'static, F: QueryFilter + 'static,

fn build( self, world: &mut World, system_meta: &mut SystemMeta, ) -> QueryState<D, F>

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

fn build_state(self, world: &mut World) -> SystemState<P>

Create a SystemState from a SystemParamBuilder. To create a system, call SystemState::build_system on the result.

impl<D, F> Copy for Query<'_, '_, D, F>

where D: ReadOnlyQueryData, F: QueryFilter,

impl<'w, 's, D, F> ReadOnlySystemParam for Query<'w, 's, D, F>

where D: ReadOnlyQueryData + 'static, F: QueryFilter + 'static,