Struct bevy::ecs::system::Query

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

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

Enables access to entity identifiers and components from a system, without the need to directly access the world. Its iterators and getter methods return query items. Each query item is a type containing data relative to an entity.

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

• D (query data). The type of data contained in the query item. Only entities that match the requested data will generate an item. Must implement the QueryData trait.
• F (query filter). A set of conditions that determines whether query items should be kept or discarded. Must implement the QueryFilter trait. This type parameter is optional.

System parameter declaration

A query should always be declared as a system parameter. This section shows the most common idioms involving the declaration of Query.

Component access

A query defined with a reference to a component as the query fetch type parameter can be used to generate items that refer to the data of said component.

// A component can be accessed by shared reference...
query: Query<&ComponentA>

// ... or by mutable reference.
query: Query<&mut ComponentA>

Query filtering

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

// Just `ComponentA` data will be accessed, but only for entities that also contain
// `ComponentB`.
query: Query<&ComponentA, With<ComponentB>>

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.

query: Query<(&ComponentA, &ComponentB), (With<ComponentC>, Without<ComponentD>)>

Entity identifier access

The identifier of an entity can be made available inside the query item by including Entity in the query fetch type parameter.

query: Query<(Entity, &ComponentA)>

Optional component access

A component can be made optional in a query by wrapping it into an Option. In this way, a query item can still be generated even if the queried entity does not contain the wrapped component. In this case, its corresponding value will be None.

// Generates items for entities that contain `ComponentA`, and optionally `ComponentB`.
query: Query<(&ComponentA, Option<&ComponentB>)>

See the documentation for AnyOf to idiomatically declare many optional components.

See the performance section to learn more about the impact of optional components.

Disjoint queries

A system cannot contain two queries that break Rust’s mutability rules. In this case, the Without filter can be used to disjoint them.

In the following example, two queries mutably access the same component. Executing this system will panic, since an entity could potentially match the two queries at the same time by having both Player and Enemy components. This would violate mutability rules.

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 this way, any entity that has both Player and Enemy components is 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 to this idiom is to wrap the conflicting queries into a ParamSet.

Whole Entity Access

EntityRefs can be fetched from a query. This will give read-only access to any component on the entity, and can be use to dynamically fetch any component without baking it into the query type. Due to this global access to the entity, this will block any other system from parallelizing with it. As such these queries should be sparingly used.

query: Query<(EntityRef, &ComponentA)>

As EntityRef can read any component on an entity, a query using it will conflict with any mutable access. It is strongly advised to couple EntityRef queries with the use of either With/Without filters or ParamSets. This also limits the scope of the query, which will improve iteration performance and also allows it to parallelize with other non-conflicting systems.

// This will panic!
query: Query<(EntityRef, &mut ComponentA)>

// This will not panic.
query_a: Query<EntityRef, With<ComponentA>>,
query_b: Query<&mut ComponentB, Without<ComponentA>>,

Accessing query items

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

Query methods	Effect
iter[_mut]	Returns an iterator over all query items.
for_each[_mut], par_iter[_mut]	Runs a specified function for each query item.
iter_many[_mut]	Iterates or runs a specified function over query items generated by a list of entities.
iter_combinations[_mut]	Returns an iterator over all combinations of a specified number of query items.
get[_mut]	Returns the query item for the specified entity.
many[_mut], get_many[_mut]	Returns the query items for the specified entities.
single[_mut], get_single[_mut]	Returns the query item while verifying that there aren’t others.

There are two methods for each type of query operation: immutable and mutable (ending with _mut). When using immutable methods, the query items returned are of type ROQueryItem, a read-only version of the query item. In this circumstance, every mutable reference in the query fetch type parameter is substituted by a shared reference.

Performance

Creating a Query is a low-cost constant operation. Iterating it, on the other hand, fetches data from the world and generates items, which can have a significant computational cost.

Table component storage type is much more optimized for query iteration than SparseSet.

Two systems cannot be executed in parallel if both access the same component type where at least one of the accesses is mutable. This happens unless the executor can verify that no entity could be found in both queries.

Optional components increase the number of entities a query has to match against. This can hurt iteration performance, especially if the query solely consists of only optional components, since the query would iterate over each entity in the world.

The following table compares the computational complexity of the various methods and operations, where:

• n is the number of entities that match the query,
• r is the number of elements in a combination,
• k is the number of involved entities in the operation,
• a is the number of archetypes in the world,
• C is the binomial coefficient, used to count combinations. _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)
for_each[_mut], par_iter[_mut]	O(n)
iter_many[_mut]	O(k)
iter_combinations[_mut]	O(nCr)
get[_mut]	O(1)
(get_)many	O(k)
(get_)many_mut	O(k2)
single[_mut], get_single[_mut]	O(a)
Archetype based filtering (With, Without, Or)	O(a)
Change detection filtering (Added, Changed)	O(a + n)

for_each methods are seen to be generally faster than their iter version on worlds with high archetype fragmentation. As iterators are in general more flexible and better integrated with the rest of the Rust ecosystem, it is advised to use iter methods over for_each. It is strongly advised to only use for_each if it tangibly improves performance: be sure profile or benchmark both before and after the change.

Implementations

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

where D: QueryData, F: QueryFilter,

pub fn to_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.

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

Returns an Iterator over the read-only query items.

Example

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

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.
• for_each for the closure based alternative.

Examples found in repository

examples/ecs/system_param.rs (line 31)

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

examples/ecs/one_shot_systems.rs (line 26)

fn count_entities(all_entities: Query<()>) {
    dbg!(all_entities.iter().count());
}

#[derive(Component)]
struct Callback(SystemId);

#[derive(Component)]
struct Triggered;

fn setup(world: &mut World) {
    let button_pressed_id = world.register_system(button_pressed);
    world.spawn((Callback(button_pressed_id), Triggered));
    // This entity does not have a Triggered component, so its callback won't run.
    let slider_toggled_id = world.register_system(slider_toggled);
    world.spawn(Callback(slider_toggled_id));
    world.run_system_once(count_entities);
}

fn button_pressed() {
    println!("A button was pressed!");
}

fn slider_toggled() {
    println!("A slider was toggled!");
}

/// Runs the systems associated with each `Callback` component if the entity also has a Triggered component.
///
/// This could be done in an exclusive system rather than using `Commands` if preferred.
fn evaluate_callbacks(query: Query<&Callback, With<Triggered>>, mut commands: Commands) {
    for callback in query.iter() {
        commands.run_system(callback.0);
    }
}

examples/stress_tests/many_animated_sprites.rs (line 149)

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 128)

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 147)

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 Ok(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<GlobalLightMeta>,
) {
    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/removal_detection.rs (line 47)

fn remove_component(
    time: Res<Time>,
    mut commands: Commands,
    query: Query<Entity, With<MyComponent>>,
) {
    // After two seconds have passed the `Component` is removed.
    if time.elapsed_seconds() > 2.0 {
        if let Some(entity) = query.iter().next() {
            commands.entity(entity).remove::<MyComponent>();
        }
    }
}

Additional examples can be found in:

• examples/stress_tests/many_cubes.rs
• examples/3d/reflection_probes.rs
• examples/stress_tests/many_foxes.rs
• examples/3d/animated_material.rs
• examples/asset/asset_decompression.rs
• examples/3d/irradiance_volumes.rs
• examples/2d/bounding_2d.rs
• examples/3d/shadow_caster_receiver.rs
• examples/3d/lightmaps.rs
• examples/math/render_primitives.rs
• examples/ui/size_constraints.rs

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

Returns an Iterator over the query items.

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.
• for_each_mut for the closure based alternative.

Examples found in repository

examples/2d/bounding_2d.rs (line 36)

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_seconds() / 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: Query<&mut Text>, cur_state: Res<State<Test>>) {
    if !cur_state.is_changed() {
        return;
    }

    let mut text = text.single_mut();
    let text = &mut text.sections[0].value;
    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 = Color::GRAY;
    for (shape, transform) in query.iter() {
        let translation = transform.translation.xy();
        let rotation = transform.rotation.to_euler(EulerRot::YXZ).2;
        match shape {
            Shape::Rectangle(r) => {
                gizmos.primitive_2d(*r, translation, rotation, color);
            }
            Shape::Circle(c) => {
                gizmos.primitive_2d(*c, translation, rotation, color);
            }
            Shape::Triangle(t) => {
                gizmos.primitive_2d(*t, translation, rotation, color);
            }
            Shape::Line(l) => {
                gizmos.primitive_2d(*l, translation, rotation, color);
            }
            Shape::Capsule(c) => {
                gizmos.primitive_2d(*c, translation, rotation, color);
            }
            Shape::Polygon(p) => {
                gizmos.primitive_2d(*p, translation, rotation, 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;
        match desired_volume {
            DesiredVolume::Aabb => {
                let aabb = match shape {
                    Shape::Rectangle(r) => r.aabb_2d(translation, rotation),
                    Shape::Circle(c) => c.aabb_2d(translation, rotation),
                    Shape::Triangle(t) => t.aabb_2d(translation, rotation),
                    Shape::Line(l) => l.aabb_2d(translation, rotation),
                    Shape::Capsule(c) => c.aabb_2d(translation, rotation),
                    Shape::Polygon(p) => p.aabb_2d(translation, rotation),
                };
                commands.entity(entity).insert(CurrentVolume::Aabb(aabb));
            }
            DesiredVolume::Circle => {
                let circle = match shape {
                    Shape::Rectangle(r) => r.bounding_circle(translation, rotation),
                    Shape::Circle(c) => c.bounding_circle(translation, rotation),
                    Shape::Triangle(t) => t.bounding_circle(translation, rotation),
                    Shape::Line(l) => l.bounding_circle(translation, rotation),
                    Shape::Capsule(c) => c.bounding_circle(translation, rotation),
                    Shape::Polygon(p) => p.bounding_circle(translation, rotation),
                };
                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 {
            Color::CYAN
        } else {
            Color::ORANGE_RED
        };
        match volume {
            CurrentVolume::Aabb(a) => {
                gizmos.rect_2d(a.center(), 0., 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, loader: Res<AssetServer>) {
    commands.spawn(Camera2dBundle::default());
    commands.spawn((
        SpatialBundle {
            transform: Transform::from_xyz(-OFFSET_X, OFFSET_Y, 0.),
            ..default()
        },
        Shape::Circle(Circle::new(45.)),
        DesiredVolume::Aabb,
        Intersects::default(),
    ));

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

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

    commands.spawn((
        SpatialBundle {
            transform: Transform::from_xyz(-OFFSET_X, -OFFSET_Y, 0.),
            ..default()
        },
        Shape::Line(Segment2d::new(Direction2d::from_xy(1., 0.3).unwrap(), 90.)),
        Spin,
        DesiredVolume::Circle,
        Intersects::default(),
    ));

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

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

    commands.spawn(
        TextBundle::from_section(
            "",
            TextStyle {
                font: loader.load("fonts/FiraMono-Medium.ttf"),
                font_size: 26.0,
                ..default()
            },
        )
        .with_style(Style {
            position_type: PositionType::Absolute,
            bottom: Val::Px(10.0),
            left: Val::Px(10.0),
            ..default()
        }),
    );
}

fn draw_ray(gizmos: &mut Gizmos, ray: &RayCast2d) {
    gizmos.line_2d(
        ray.ray.origin,
        ray.ray.origin + *ray.ray.direction * ray.max,
        Color::WHITE,
    );
    for r in [1., 2., 3.] {
        gizmos.circle_2d(ray.ray.origin, r, Color::FUCHSIA);
    }
}

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

    let aabb_ray = Ray2d {
        origin: ray * 250.,
        direction: Direction2d::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 {
            for r in [1., 2., 3.] {
                gizmos.circle_2d(
                    ray_cast.ray.origin + *ray_cast.ray.direction * toi,
                    r,
                    Color::GREEN,
                );
            }
        }
    }
}

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.center(),
                0.,
                aabb_cast.aabb.half_size() * 2.,
                Color::GREEN,
            );
        }
    }
}

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.center(),
                circle_cast.circle.radius(),
                Color::GREEN,
            );
        }
    }
}

fn get_intersection_position(time: &Time) -> Vec2 {
    let x = (0.8 * time.elapsed_seconds()).cos() * 250.;
    let y = (0.4 * time.elapsed_seconds()).sin() * 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, 0., aabb.half_size() * 2., Color::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(), Color::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/irradiance_volumes.rs (line 321)

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

impl AppStatus {
    // Constructs the help text at the bottom of the screen based on the
    // application status.
    fn create_text(&self, asset_server: &AssetServer) -> 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,
        };

        Text::from_section(
            format!(
                "{}\n{}\n{}\n{}\n{}",
                CLICK_TO_MOVE_HELP_TEXT,
                voxels_help_text,
                irradiance_volume_help_text,
                rotation_help_text,
                switch_mesh_help_text
            ),
            TextStyle {
                font: asset_server.load("fonts/FiraMono-Medium.ttf"),
                font_size: 24.0,
                color: Color::ANTIQUE_WHITE,
            },
        )
    }
}

// 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_seconds())
            .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<Handle<Mesh>>, Without<Handle<Scene>>),
    >,
    mut fox_query: Query<&mut Visibility, (With<MainObject>, With<Handle<Scene>>)>,
) {
    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,
        });
        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| 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 Some(ray) = camera.viewport_to_world(camera_transform, mouse_position) else {
        return;
    };
    let Some(ray_distance) = ray.intersect_plane(Vec3::ZERO, Plane3d::new(Vec3::Y)) else {
        return;
    };
    let plane_intersection = ray.origin + ray.direction.normalize() * ray_distance;

    // Move all the main objeccts.
    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 {
        // Load all the assets.
        let asset_server = world.resource::<AssetServer>();
        let fox = asset_server.load("models/animated/Fox.glb#Scene0");
        let main_scene =
            asset_server.load("models/IrradianceVolumeExample/IrradianceVolumeExample.glb#Scene0");
        let irradiance_volume = asset_server.load::<Image>("irradiance_volumes/Example.vxgi.ktx2");
        let fox_animation =
            asset_server.load::<AnimationClip>("models/animated/Fox.glb#Animation1");

        // 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.
        let skybox = asset_server.load::<Image>("environment_maps/pisa_specular_rgb9e5_zstd.ktx2");

        let mut mesh_assets = world.resource_mut::<Assets<Mesh>>();
        let main_sphere = mesh_assets.add(Sphere::default().mesh().uv(32, 18));
        let voxel_cube = mesh_assets.add(Cuboid::default());

        let mut standard_material_assets = world.resource_mut::<Assets<StandardMaterial>>();
        let main_material = standard_material_assets.add(Color::SILVER);

        ExampleAssets {
            main_sphere,
            fox,
            main_sphere_material: main_material,
            main_scene,
            irradiance_volume,
            fox_animation,
            voxel_cube,
            skybox,
        }
    }
}

// Plays the animation on the fox.
fn play_animations(assets: Res<ExampleAssets>, mut players: Query<&mut AnimationPlayer>) {
    for mut player in players.iter_mut() {
        // This will safely do nothing if the animation is already playing.
        player.play(assets.fox_animation.clone()).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::RED),
            extension: VoxelVisualizationExtension {
                irradiance_volume_info: VoxelVisualizationIrradianceVolumeInfo {
                    transform: VOXEL_TRANSFORM.inverse(),
                    inverse_transform: VOXEL_TRANSFORM,
                    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(MaterialMeshBundle {
                            mesh: example_assets.voxel_cube.clone(),
                            material: voxel_cube_material.clone(),
                            transform: Transform::from_scale(Vec3::splat(VOXEL_CUBE_SCALE))
                                .with_translation(pos),
                            ..default()
                        })
                        .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 249)

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

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, asset_server: &AssetServer) -> Text {
        let rotation_help_text = if self.rotating {
            STOP_ROTATION_HELP_TEXT
        } else {
            START_ROTATION_HELP_TEXT
        };

        Text::from_section(
            format!(
                "{}\n{}\n{}",
                self.reflection_mode, rotation_help_text, REFLECTION_MODE_HELP_TEXT
            ),
            TextStyle {
                font: asset_server.load("fonts/FiraMono-Medium.ttf"),
                font_size: 24.0,
                color: Color::ANTIQUE_WHITE,
            },
        )
    }
}

// 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,
    }
}

// Rotates the camera a bit every frame.
fn rotate_camera(
    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(ROTATION_SPEED)
            .rotate(transform.translation.xz())
            .extend(transform.translation.y)
            .xzy();
        transform.look_at(Vec3::ZERO, Vec3::Y);
    }
}

examples/stress_tests/text_pipeline.rs (line 76)

fn update_text_bounds(time: Res<Time>, mut text_bounds_query: Query<&mut Text2dBounds>) {
    let width = (1. + time.elapsed_seconds().sin()) * 600.0;
    for mut text_bounds in text_bounds_query.iter_mut() {
        text_bounds.size.x = width;
    }
}

examples/shader/shader_prepass.rs (line 190)

fn rotate(mut q: Query<&mut Transform, With<Rotates>>, time: Res<Time>) {
    for mut t in q.iter_mut() {
        let rot = (time.elapsed_seconds().sin() * 0.5 + 0.5) * std::f32::consts::PI * 2.0;
        t.rotation = Quat::from_rotation_z(rot);
    }
}

examples/3d/bloom_3d.rs (line 234)

fn bounce_spheres(time: Res<Time>, mut query: Query<&mut Transform, With<Bouncing>>) {
    for mut transform in query.iter_mut() {
        transform.translation.y =
            (transform.translation.x + transform.translation.z + time.elapsed_seconds()).sin();
    }
}

Additional examples can be found in:

• examples/3d/parallax_mapping.rs
• examples/input/text_input.rs
• examples/3d/deferred_rendering.rs
• examples/ui/overflow.rs
• examples/stress_tests/many_animated_sprites.rs
• examples/audio/spatial_audio_2d.rs
• examples/time/virtual_time.rs
• examples/3d/spotlight.rs
• examples/audio/spatial_audio_3d.rs
• examples/ui/viewport_debug.rs
• examples/3d/tonemapping.rs
• examples/math/render_primitives.rs
• examples/ui/display_and_visibility.rs
• examples/stress_tests/many_buttons.rs
• examples/games/alien_cake_addict.rs
• examples/ui/size_constraints.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.

Example

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

See also

• iter_combinations_mut for mutable query item combinations.

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.

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.

Examples found in repository

examples/ecs/iter_combinations.rs (line 127)

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

where EntityList: IntoIterator, <EntityList as IntoIterator>::Item: Borrow<Entity>,

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. 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.

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: Borrow<Entity>,

Returns an iterator over the 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.

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;
        }
    }
}

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

Returns an Iterator over the query items.

Safety

This function makes it possible to violate Rust’s aliasing guarantees. You must make sure this call does not result in multiple mutable references to the same component.

See also

• iter 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.

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: Borrow<Entity>,

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

Safety

This allows aliased mutability and does not check for entity uniqueness. You must make sure this call does not result in multiple mutable references to the same component. Particular care must be taken when collecting the data (rather than iterating over it one item at a time) such as via Iterator::collect.

See also

• iter_many_mut to safely access the query items.

pub fn for_each<'this>( &'this self, f: impl FnMut(<<D as QueryData>::ReadOnly as WorldQuery>::Item<'this>) )

👎Deprecated since 0.13.0: Query::for_each was not idiomatic Rust and has been moved to query.iter().for_each()

Runs f on each read-only query item.

Shorthand for query.iter().for_each(..).

Example

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

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

See also

• for_each_mut to operate on mutable query items.
• iter for the iterator based alternative.

pub fn for_each_mut<'a>( &'a mut self, f: impl FnMut(<D as WorldQuery>::Item<'a>) )

👎Deprecated since 0.13.0: Query::for_each_mut was not idiomatic Rust and has been moved to query.iter_mut().for_each()

Runs f on each query item.

Shorthand for query.iter_mut().for_each(..).

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.for_each_mut(|mut velocity| {
        velocity.y -= 9.8 * DELTA;
    });
}

See also

• for_each to operate on read-only query items.
• iter_mut for the iterator based alternative.

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

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

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 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 37)

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(windows: Query<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
    let window = windows.single();
    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 get( &self, entity: Entity ) -> Result<<<D as QueryData>::ReadOnly as WorldQuery>::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.

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/ui/ui.rs (line 323)

fn mouse_scroll(
    mut mouse_wheel_events: EventReader<MouseWheel>,
    mut query_list: Query<(&mut ScrollingList, &mut Style, &Parent, &Node)>,
    query_node: Query<&Node>,
) {
    for mouse_wheel_event in mouse_wheel_events.read() {
        for (mut scrolling_list, mut style, parent, list_node) in &mut query_list {
            let items_height = list_node.size().y;
            let container_height = query_node.get(parent.get()).unwrap().size().y;

            let max_scroll = (items_height - container_height).max(0.);

            let dy = match mouse_wheel_event.unit {
                MouseScrollUnit::Line => mouse_wheel_event.y * 20.,
                MouseScrollUnit::Pixel => mouse_wheel_event.y,
            };

            scrolling_list.position += dy;
            scrolling_list.position = scrolling_list.position.clamp(-max_scroll, 0.);
            style.top = Val::Px(scrolling_list.position);
        }
    }
}

examples/animation/gltf_skinned_mesh.rs (line 58)

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

        // First joint is the second child of the mesh node.
        let first_joint_entity = mesh_node_children[1];
        // Get `Children` in the first joint.
        let first_joint_children = children_query.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 * time.elapsed_seconds().sin());
    }
}

examples/3d/split_screen.rs (line 205)

fn set_camera_viewports(
    windows: Query<&Window>,
    mut resize_events: EventReader<WindowResized>,
    mut left_camera: Query<&mut Camera, (With<LeftCamera>, Without<RightCamera>)>,
    mut right_camera: Query<&mut Camera, With<RightCamera>>,
) {
    // 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 mut left_camera = left_camera.single_mut();
        left_camera.viewport = Some(Viewport {
            physical_position: UVec2::new(0, 0),
            physical_size: UVec2::new(
                window.resolution.physical_width() / 2,
                window.resolution.physical_height(),
            ),
            ..default()
        });

        let mut right_camera = right_camera.single_mut();
        right_camera.viewport = Some(Viewport {
            physical_position: UVec2::new(window.resolution.physical_width() / 2, 0),
            physical_size: UVec2::new(
                window.resolution.physical_width() / 2,
                window.resolution.physical_height(),
            ),
            ..default()
        });
    }
}

examples/games/alien_cake_addict.rs (line 270)

fn focus_camera(
    time: Res<Time>,
    mut game: ResMut<Game>,
    mut transforms: ParamSet<(Query<&mut Transform, With<Camera3d>>, Query<&Transform>)>,
) {
    const SPEED: f32 = 2.0;
    // if there is both a player and a bonus, target the mid-point of them
    if let (Some(player_entity), Some(bonus_entity)) = (game.player.entity, game.bonus.entity) {
        let transform_query = transforms.p1();
        if let (Ok(player_transform), Ok(bonus_transform)) = (
            transform_query.get(player_entity),
            transform_query.get(bonus_entity),
        ) {
            game.camera_should_focus = player_transform
                .translation
                .lerp(bonus_transform.translation, 0.5);
        }
        // otherwise, if there is only a player, target the player
    } else if let Some(player_entity) = game.player.entity {
        if let Ok(player_transform) = transforms.p1().get(player_entity) {
            game.camera_should_focus = player_transform.translation;
        }
        // otherwise, target the middle
    } else {
        game.camera_should_focus = Vec3::from(RESET_FOCUS);
    }
    // calculate the camera motion based on the difference between where the camera is looking
    // and where it should be looking; the greater the distance, the faster the motion;
    // smooth out the camera movement using the frame time
    let mut camera_motion = game.camera_should_focus - game.camera_is_focus;
    if camera_motion.length() > 0.2 {
        camera_motion *= SPEED * time.delta_seconds();
        // set the new camera's actual focus
        game.camera_is_focus += camera_motion;
    }
    // look at that new camera's actual focus
    for mut transform in transforms.p0().iter_mut() {
        *transform = transform.looking_at(game.camera_is_focus, Vec3::Y);
    }
}

examples/3d/blend_modes.rs (line 332)

fn example_control_system(
    mut materials: ResMut<Assets<StandardMaterial>>,
    controllable: Query<(&Handle<StandardMaterial>, &ExampleControls)>,
    mut camera: Query<(&mut Camera, &mut Transform, &GlobalTransform), With<Camera3d>>,
    mut labels: Query<(&mut Style, &ExampleLabel)>,
    mut display: Query<&mut Text, With<ExampleDisplay>>,
    labelled: Query<&GlobalTransform>,
    mut state: Local<ExampleState>,
    time: Res<Time>,
    input: Res<ButtonInput<KeyCode>>,
) {
    if input.pressed(KeyCode::ArrowUp) {
        state.alpha = (state.alpha + time.delta_seconds()).min(1.0);
    } else if input.pressed(KeyCode::ArrowDown) {
        state.alpha = (state.alpha - time.delta_seconds()).max(0.0);
    }

    if input.just_pressed(KeyCode::Space) {
        state.unlit = !state.unlit;
    }

    let randomize_colors = input.just_pressed(KeyCode::KeyC);

    for (material_handle, controls) in &controllable {
        let material = materials.get_mut(material_handle).unwrap();
        material.base_color.set_a(state.alpha);

        if controls.color && randomize_colors {
            material.base_color.set_r(random());
            material.base_color.set_g(random());
            material.base_color.set_b(random());
        }
        if controls.unlit {
            material.unlit = state.unlit;
        }
    }

    let (mut camera, mut camera_transform, camera_global_transform) = camera.single_mut();

    if input.just_pressed(KeyCode::KeyH) {
        camera.hdr = !camera.hdr;
    }

    let rotation = if input.pressed(KeyCode::ArrowLeft) {
        time.delta_seconds()
    } else if input.pressed(KeyCode::ArrowRight) {
        -time.delta_seconds()
    } else {
        0.0
    };

    camera_transform.rotate_around(Vec3::ZERO, Quat::from_rotation_y(rotation));

    for (mut style, label) in &mut labels {
        let world_position = labelled.get(label.entity).unwrap().translation() + Vec3::Y;

        let viewport_position = camera
            .world_to_viewport(camera_global_transform, world_position)
            .unwrap();

        style.top = Val::Px(viewport_position.y);
        style.left = Val::Px(viewport_position.x);
    }

    let mut display = display.single_mut();
    display.sections[0].value = format!(
        "  HDR: {}\nAlpha: {:.2}",
        if camera.hdr { "ON " } else { "OFF" },
        state.alpha
    );
}

examples/ui/size_constraints.rs (line 328)

fn update_buttons(
    mut button_query: Query<
        (Entity, &Interaction, &Constraint, &ButtonValue),
        Changed<Interaction>,
    >,
    mut bar_query: Query<&mut Style, With<Bar>>,
    mut text_query: Query<&mut Text>,
    children_query: Query<&Children>,
    mut button_activated_event: EventWriter<ButtonActivatedEvent>,
) {
    let mut style = bar_query.single_mut();
    for (button_id, interaction, constraint, value) in button_query.iter_mut() {
        match interaction {
            Interaction::Pressed => {
                button_activated_event.send(ButtonActivatedEvent(button_id));
                match constraint {
                    Constraint::FlexBasis => {
                        style.flex_basis = value.0;
                    }
                    Constraint::Width => {
                        style.width = value.0;
                    }
                    Constraint::MinWidth => {
                        style.min_width = value.0;
                    }
                    Constraint::MaxWidth => {
                        style.max_width = value.0;
                    }
                }
            }
            Interaction::Hovered => {
                if let Ok(children) = children_query.get(button_id) {
                    for &child in children {
                        if let Ok(grand_children) = children_query.get(child) {
                            for &grandchild in grand_children {
                                if let Ok(mut text) = text_query.get_mut(grandchild) {
                                    if text.sections[0].style.color != ACTIVE_TEXT_COLOR {
                                        text.sections[0].style.color = HOVERED_TEXT_COLOR;
                                    }
                                }
                            }
                        }
                    }
                }
            }
            Interaction::None => {
                if let Ok(children) = children_query.get(button_id) {
                    for &child in children {
                        if let Ok(grand_children) = children_query.get(child) {
                            for &grandchild in grand_children {
                                if let Ok(mut text) = text_query.get_mut(grandchild) {
                                    if text.sections[0].style.color != ACTIVE_TEXT_COLOR {
                                        text.sections[0].style.color = UNHOVERED_TEXT_COLOR;
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

fn update_radio_buttons_colors(
    mut event_reader: EventReader<ButtonActivatedEvent>,
    button_query: Query<(Entity, &Constraint, &Interaction)>,
    mut color_query: Query<&mut BackgroundColor>,
    mut text_query: Query<&mut Text>,
    children_query: Query<&Children>,
) {
    for &ButtonActivatedEvent(button_id) in event_reader.read() {
        let (_, target_constraint, _) = button_query.get(button_id).unwrap();
        for (id, constraint, interaction) in button_query.iter() {
            if target_constraint == constraint {
                let (border_color, inner_color, text_color) = if id == button_id {
                    (ACTIVE_BORDER_COLOR, ACTIVE_INNER_COLOR, ACTIVE_TEXT_COLOR)
                } else {
                    (
                        INACTIVE_BORDER_COLOR,
                        INACTIVE_INNER_COLOR,
                        if matches!(interaction, Interaction::Hovered) {
                            HOVERED_TEXT_COLOR
                        } else {
                            UNHOVERED_TEXT_COLOR
                        },
                    )
                };

                color_query.get_mut(id).unwrap().0 = border_color;
                if let Ok(children) = children_query.get(id) {
                    for &child in children {
                        color_query.get_mut(child).unwrap().0 = inner_color;
                        if let Ok(grand_children) = children_query.get(child) {
                            for &grandchild in grand_children {
                                if let Ok(mut text) = text_query.get_mut(grandchild) {
                                    text.sections[0].style.color = text_color;
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

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

See also

• get_many_mut to get mutable query items.
• many for the panicking version.

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

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 WorldQuery>::Item<'_>, QueryEntityError>

Returns the query item for the given Entity.

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

Example

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

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/ecs/removal_detection.rs (line 57)

fn react_on_removal(mut removed: RemovedComponents<MyComponent>, mut query: Query<&mut Sprite>) {
    // `RemovedComponents<T>::read()` returns an iterator with the `Entity`s that had their
    // `Component` `T` (in this case `MyComponent`) removed at some point earlier during the frame.
    for entity in removed.read() {
        if let Ok(mut sprite) = query.get_mut(entity) {
            sprite.color.set_r(0.0);
        }
    }
}

examples/3d/update_gltf_scene.rs (line 67)

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 * time.elapsed_seconds().sin() / 20.,
                    0.,
                    time.elapsed_seconds().cos() / 20.,
                );
                offset += 0.5;
            }
        }
    }
}

examples/ui/ui_texture_slice.rs (line 21)

fn button_system(
    mut interaction_query: Query<(&Interaction, &Children), (Changed<Interaction>, With<Button>)>,
    mut text_query: Query<&mut Text>,
) {
    for (interaction, children) in &mut interaction_query {
        let mut text = text_query.get_mut(children[0]).unwrap();
        match *interaction {
            Interaction::Pressed => {
                text.sections[0].value = "Press".to_string();
            }
            Interaction::Hovered => {
                text.sections[0].value = "Hover".to_string();
            }
            Interaction::None => {
                text.sections[0].value = "Button".to_string();
            }
        }
    }
}

examples/3d/split_screen.rs (line 240)

fn button_system(
    interaction_query: Query<
        (&Interaction, &TargetCamera, &RotateCamera),
        (Changed<Interaction>, With<Button>),
    >,
    mut camera_query: Query<&mut Transform, With<Camera>>,
) {
    for (interaction, target_camera, RotateCamera(direction)) in &interaction_query {
        if let Interaction::Pressed = *interaction {
            // Since TargetCamera propagates to the children, we can use it to find
            // which side of the screen the button is on.
            if let Ok(mut camera_transform) = camera_query.get_mut(target_camera.entity()) {
                let angle = match direction {
                    Direction::Left => -0.1,
                    Direction::Right => 0.1,
                };
                camera_transform.rotate_around(Vec3::ZERO, Quat::from_axis_angle(Vec3::Y, angle));
            }
        }
    }
}

examples/ui/display_and_visibility.rs (line 443)

fn buttons_handler<T>(
    mut left_panel_query: Query<&mut <Target<T> as TargetUpdate>::TargetComponent>,
    mut visibility_button_query: Query<(&Target<T>, &Interaction, &Children), Changed<Interaction>>,
    mut text_query: Query<&mut Text>,
) where
    T: Send + Sync,
    Target<T>: TargetUpdate + Component,
{
    for (target, interaction, children) in visibility_button_query.iter_mut() {
        if matches!(interaction, Interaction::Pressed) {
            let mut target_value = left_panel_query.get_mut(target.id).unwrap();
            for &child in children {
                if let Ok(mut text) = text_query.get_mut(child) {
                    text.sections[0].value = target.update_target(target_value.as_mut());
                    text.sections[0].style.color = if text.sections[0].value.contains("None")
                        || text.sections[0].value.contains("Hidden")
                    {
                        Color::rgb(1.0, 0.7, 0.7)
                    } else {
                        Color::WHITE
                    };
                }
            }
        }
    }
}

fn text_hover(
    mut button_query: Query<(&Interaction, &mut BackgroundColor, &Children), Changed<Interaction>>,
    mut text_query: Query<&mut Text>,
) {
    for (interaction, mut background_color, children) in button_query.iter_mut() {
        match interaction {
            Interaction::Hovered => {
                *background_color = BackgroundColor(Color::BLACK.with_a(0.6));
                for &child in children {
                    if let Ok(mut text) = text_query.get_mut(child) {
                        // Bypass change detection to avoid recomputation of the text when only changing the color
                        text.bypass_change_detection().sections[0].style.color = Color::YELLOW;
                    }
                }
            }
            _ => {
                *background_color = BackgroundColor(Color::BLACK.with_a(0.5));
                for &child in children {
                    if let Ok(mut text) = text_query.get_mut(child) {
                        text.bypass_change_detection().sections[0].style.color =
                            if text.sections[0].value.contains("None")
                                || text.sections[0].value.contains("Hidden")
                            {
                                HIDDEN_COLOR
                            } else {
                                Color::WHITE
                            };
                    }
                }
            }
        }
    }
}

examples/ui/button.rs (line 33)

fn button_system(
    mut interaction_query: Query<
        (
            &Interaction,
            &mut BackgroundColor,
            &mut BorderColor,
            &Children,
        ),
        (Changed<Interaction>, With<Button>),
    >,
    mut text_query: Query<&mut Text>,
) {
    for (interaction, mut color, mut border_color, children) in &mut interaction_query {
        let mut text = text_query.get_mut(children[0]).unwrap();
        match *interaction {
            Interaction::Pressed => {
                text.sections[0].value = "Press".to_string();
                *color = PRESSED_BUTTON.into();
                border_color.0 = Color::RED;
            }
            Interaction::Hovered => {
                text.sections[0].value = "Hover".to_string();
                *color = HOVERED_BUTTON.into();
                border_color.0 = Color::WHITE;
            }
            Interaction::None => {
                text.sections[0].value = "Button".to_string();
                *color = NORMAL_BUTTON.into();
                border_color.0 = Color::BLACK;
            }
        }
    }
}

Additional examples can be found in:

• examples/animation/gltf_skinned_mesh.rs
• examples/games/contributors.rs
• examples/ecs/hierarchy.rs
• examples/games/alien_cake_addict.rs
• examples/ui/size_constraints.rs

pub fn get_many_mut<const N: usize>( &mut self, entities: [Entity; N] ) -> Result<[<D as WorldQuery>::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.

See also

• get_many to get read-only query items.
• many_mut for the panicking version.

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

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 WorldQuery>::Item<'_>, QueryEntityError>

Returns the query item for the given Entity.

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

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 get_component<T>( &self, entity: Entity ) -> Result<&T, QueryComponentError>

where T: Component,

👎Deprecated since 0.13.0: Please use get and select for the exact component based on the structure of the exact query as required.

Returns a shared reference to the component T of the given Entity.

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

Example

Here, get_component is used to retrieve the Character component 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_component::<Character>(selection.entity) {
        println!("{}", selected_character.name);
    }
}

See also

• component a panicking version of this function.
• get_component_mut to get a mutable reference of a component.

pub fn get_component_mut<T>( &mut self, entity: Entity ) -> Result<Mut<'_, T>, QueryComponentError>

where T: Component,

👎Deprecated since 0.13.0: Please use get_mut and select for the exact component based on the structure of the exact query as required.

Returns a mutable reference to the component T of the given entity.

In case of a nonexisting entity, mismatched component or missing write access, a QueryComponentError is returned instead.

Example

Here, get_component_mut is used to retrieve the Health component 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_component_mut::<Health>(poisoned.character_id) {
        health.0 -= 1;
    }
}

See also

• component_mut a panicking version of this function.
• get_component to get a shared reference of a component.

pub fn component<T>(&self, entity: Entity) -> &T

where T: Component,

👎Deprecated since 0.13.0: Please use get and select for the exact component based on the structure of the exact query as required.

Returns a shared reference to the component T of the given Entity.

Panics

Panics in case of a nonexisting entity or mismatched component.

See also

• get_component a non-panicking version of this function.
• component_mut to get a mutable reference of a component.

pub fn component_mut<T>(&mut self, entity: Entity) -> Mut<'_, T>

where T: Component,

👎Deprecated since 0.13.0: Please use get_mut and select for the exact component based on the structure of the exact query as required.

Returns a mutable reference to the component T of the given entity.

Panics

Panics in case of a nonexisting entity, mismatched component or missing write access.

See also

• get_component_mut a non-panicking version of this function.
• component to get a shared reference of a component.

pub unsafe fn get_component_unchecked_mut<T>( &self, entity: Entity ) -> Result<Mut<'_, T>, QueryComponentError>

where T: Component,

👎Deprecated since 0.13.0: Please use get_unchecked and select for the exact component based on the structure of the exact query as required.

Returns a mutable reference to the component T of the given entity.

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

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_component_mut for the safe version.

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

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

Panics

This method panics if the number of query items is not exactly one.

Example

fn player_system(query: Query<&Position, With<Player>>) {
    let player_position = query.single();
    // do something with player_position
}

See also

• get_single for the non-panicking version.
• single_mut to get the mutable query item.

Examples found in repository

examples/ecs/iter_combinations.rs (line 159)

fn look_at_star(
    mut camera: Query<&mut Transform, (With<Camera>, Without<Star>)>,
    star: Query<&Transform, With<Star>>,
) {
    let mut camera = camera.single_mut();
    let star = star.single();
    let new_rotation = camera
        .looking_at(star.translation, Vec3::Y)
        .rotation
        .lerp(camera.rotation, 0.1);
    camera.rotation = new_rotation;
}

examples/window/screenshot.rs (line 25)

fn screenshot_on_spacebar(
    input: Res<ButtonInput<KeyCode>>,
    main_window: Query<Entity, With<PrimaryWindow>>,
    mut screenshot_manager: ResMut<ScreenshotManager>,
    mut counter: Local<u32>,
) {
    if input.just_pressed(KeyCode::Space) {
        let path = format!("./screenshot-{}.png", *counter);
        *counter += 1;
        screenshot_manager
            .save_screenshot_to_disk(main_window.single(), path)
            .unwrap();
    }
}

examples/2d/2d_viewport_to_world.rs (line 18)

fn draw_cursor(
    camera_query: Query<(&Camera, &GlobalTransform)>,
    windows: Query<&Window>,
    mut gizmos: Gizmos,
) {
    let (camera, camera_transform) = camera_query.single();

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

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

    gizmos.circle_2d(point, 10., Color::WHITE);
}

examples/stress_tests/bevymark.rs (line 159)

fn scheduled_spawner(
    mut commands: Commands,
    args: Res<Args>,
    windows: Query<&Window>,
    mut scheduled: ResMut<BirdScheduled>,
    mut counter: ResMut<BevyCounter>,
    bird_resources: ResMut<BirdResources>,
) {
    let window = windows.single();

    if scheduled.waves > 0 {
        let bird_resources = bird_resources.into_inner();
        spawn_birds(
            &mut commands,
            args.into_inner(),
            &window.resolution,
            &mut counter,
            scheduled.per_wave,
            bird_resources,
            None,
            scheduled.waves - 1,
        );

        scheduled.waves -= 1;
    }
}

#[derive(Resource)]
struct BirdResources {
    textures: Vec<Handle<Image>>,
    materials: Vec<Handle<ColorMaterial>>,
    quad: Mesh2dHandle,
    color_rng: StdRng,
    material_rng: StdRng,
    velocity_rng: StdRng,
    transform_rng: StdRng,
}

#[derive(Component)]
struct StatsText;

#[allow(clippy::too_many_arguments)]
fn setup(
    mut commands: Commands,
    args: Res<Args>,
    asset_server: Res<AssetServer>,
    mut meshes: ResMut<Assets<Mesh>>,
    material_assets: ResMut<Assets<ColorMaterial>>,
    images: ResMut<Assets<Image>>,
    windows: Query<&Window>,
    counter: ResMut<BevyCounter>,
) {
    warn!(include_str!("warning_string.txt"));

    let args = args.into_inner();
    let images = images.into_inner();

    let mut textures = Vec::with_capacity(args.material_texture_count.max(1));
    if matches!(args.mode, Mode::Sprite) || args.material_texture_count > 0 {
        textures.push(asset_server.load("branding/icon.png"));
    }
    init_textures(&mut textures, args, images);

    let material_assets = material_assets.into_inner();
    let materials = init_materials(args, &textures, material_assets);

    let mut bird_resources = BirdResources {
        textures,
        materials,
        quad: meshes
            .add(Rectangle::from_size(Vec2::splat(BIRD_TEXTURE_SIZE as f32)))
            .into(),
        color_rng: StdRng::seed_from_u64(42),
        material_rng: StdRng::seed_from_u64(42),
        velocity_rng: StdRng::seed_from_u64(42),
        transform_rng: StdRng::seed_from_u64(42),
    };

    let text_section = move |color, value: &str| {
        TextSection::new(
            value,
            TextStyle {
                font_size: 40.0,
                color,
                ..default()
            },
        )
    };

    commands.spawn(Camera2dBundle::default());
    commands
        .spawn(NodeBundle {
            style: Style {
                position_type: PositionType::Absolute,
                padding: UiRect::all(Val::Px(5.0)),
                ..default()
            },
            z_index: ZIndex::Global(i32::MAX),
            background_color: Color::BLACK.with_a(0.75).into(),
            ..default()
        })
        .with_children(|c| {
            c.spawn((
                TextBundle::from_sections([
                    text_section(Color::GREEN, "Bird Count: "),
                    text_section(Color::CYAN, ""),
                    text_section(Color::GREEN, "\nFPS (raw): "),
                    text_section(Color::CYAN, ""),
                    text_section(Color::GREEN, "\nFPS (SMA): "),
                    text_section(Color::CYAN, ""),
                    text_section(Color::GREEN, "\nFPS (EMA): "),
                    text_section(Color::CYAN, ""),
                ]),
                StatsText,
            ));
        });

    let mut scheduled = BirdScheduled {
        per_wave: args.per_wave,
        waves: args.waves,
    };

    if args.benchmark {
        let counter = counter.into_inner();
        for wave in (0..scheduled.waves).rev() {
            spawn_birds(
                &mut commands,
                args,
                &windows.single().resolution,
                counter,
                scheduled.per_wave,
                &mut bird_resources,
                Some(wave),
                wave,
            );
        }
        scheduled.waves = 0;
    }
    commands.insert_resource(bird_resources);
    commands.insert_resource(scheduled);
}

#[allow(clippy::too_many_arguments)]
fn mouse_handler(
    mut commands: Commands,
    args: Res<Args>,
    time: Res<Time>,
    mouse_button_input: Res<ButtonInput<MouseButton>>,
    windows: Query<&Window>,
    bird_resources: ResMut<BirdResources>,
    mut counter: ResMut<BevyCounter>,
    mut rng: Local<Option<StdRng>>,
    mut wave: Local<usize>,
) {
    if rng.is_none() {
        *rng = Some(StdRng::seed_from_u64(42));
    }
    let rng = rng.as_mut().unwrap();
    let window = windows.single();

    if mouse_button_input.just_released(MouseButton::Left) {
        counter.color = Color::rgb_linear(rng.gen(), rng.gen(), rng.gen());
    }

    if mouse_button_input.pressed(MouseButton::Left) {
        let spawn_count = (BIRDS_PER_SECOND as f64 * time.delta_seconds_f64()) as usize;
        spawn_birds(
            &mut commands,
            args.into_inner(),
            &window.resolution,
            &mut counter,
            spawn_count,
            bird_resources.into_inner(),
            None,
            *wave,
        );
        *wave += 1;
    }
}

fn bird_velocity_transform(
    half_extents: Vec2,
    mut translation: Vec3,
    velocity_rng: &mut StdRng,
    waves: Option<usize>,
    dt: f32,
) -> (Transform, Vec3) {
    let mut velocity = Vec3::new(MAX_VELOCITY * (velocity_rng.gen::<f32>() - 0.5), 0., 0.);

    if let Some(waves) = waves {
        // Step the movement and handle collisions as if the wave had been spawned at fixed time intervals
        // and with dt-spaced frames of simulation
        for _ in 0..(waves * (FIXED_TIMESTEP / dt).round() as usize) {
            step_movement(&mut translation, &mut velocity, dt);
            handle_collision(half_extents, &translation, &mut velocity);
        }
    }
    (
        Transform::from_translation(translation).with_scale(Vec3::splat(BIRD_SCALE)),
        velocity,
    )
}

const FIXED_DELTA_TIME: f32 = 1.0 / 60.0;

#[allow(clippy::too_many_arguments)]
fn spawn_birds(
    commands: &mut Commands,
    args: &Args,
    primary_window_resolution: &WindowResolution,
    counter: &mut BevyCounter,
    spawn_count: usize,
    bird_resources: &mut BirdResources,
    waves_to_simulate: Option<usize>,
    wave: usize,
) {
    let bird_x = (primary_window_resolution.width() / -2.) + HALF_BIRD_SIZE;
    let bird_y = (primary_window_resolution.height() / 2.) - HALF_BIRD_SIZE;

    let half_extents = 0.5
        * Vec2::new(
            primary_window_resolution.width(),
            primary_window_resolution.height(),
        );

    let color = counter.color;
    let current_count = counter.count;

    match args.mode {
        Mode::Sprite => {
            let batch = (0..spawn_count)
                .map(|count| {
                    let bird_z = if args.ordered_z {
                        (current_count + count) as f32 * 0.00001
                    } else {
                        bird_resources.transform_rng.gen::<f32>()
                    };

                    let (transform, velocity) = bird_velocity_transform(
                        half_extents,
                        Vec3::new(bird_x, bird_y, bird_z),
                        &mut bird_resources.velocity_rng,
                        waves_to_simulate,
                        FIXED_DELTA_TIME,
                    );

                    let color = if args.vary_per_instance {
                        Color::rgb_linear(
                            bird_resources.color_rng.gen(),
                            bird_resources.color_rng.gen(),
                            bird_resources.color_rng.gen(),
                        )
                    } else {
                        color
                    };
                    (
                        SpriteBundle {
                            texture: bird_resources
                                .textures
                                .choose(&mut bird_resources.material_rng)
                                .unwrap()
                                .clone(),
                            transform,
                            sprite: Sprite { color, ..default() },
                            ..default()
                        },
                        Bird { velocity },
                    )
                })
                .collect::<Vec<_>>();
            commands.spawn_batch(batch);
        }
        Mode::Mesh2d => {
            let batch = (0..spawn_count)
                .map(|count| {
                    let bird_z = if args.ordered_z {
                        (current_count + count) as f32 * 0.00001
                    } else {
                        bird_resources.transform_rng.gen::<f32>()
                    };

                    let (transform, velocity) = bird_velocity_transform(
                        half_extents,
                        Vec3::new(bird_x, bird_y, bird_z),
                        &mut bird_resources.velocity_rng,
                        waves_to_simulate,
                        FIXED_DELTA_TIME,
                    );

                    let material =
                        if args.vary_per_instance || args.material_texture_count > args.waves {
                            bird_resources
                                .materials
                                .choose(&mut bird_resources.material_rng)
                                .unwrap()
                                .clone()
                        } else {
                            bird_resources.materials[wave % bird_resources.materials.len()].clone()
                        };
                    (
                        MaterialMesh2dBundle {
                            mesh: bird_resources.quad.clone(),
                            material,
                            transform,
                            ..default()
                        },
                        Bird { velocity },
                    )
                })
                .collect::<Vec<_>>();
            commands.spawn_batch(batch);
        }
    }

    counter.count += spawn_count;
    counter.color = Color::rgb_linear(
        bird_resources.color_rng.gen(),
        bird_resources.color_rng.gen(),
        bird_resources.color_rng.gen(),
    );
}

fn step_movement(translation: &mut Vec3, velocity: &mut Vec3, dt: f32) {
    translation.x += velocity.x * dt;
    translation.y += velocity.y * dt;
    velocity.y += GRAVITY * dt;
}

fn movement_system(
    args: Res<Args>,
    time: Res<Time>,
    mut bird_query: Query<(&mut Bird, &mut Transform)>,
) {
    let dt = if args.benchmark {
        FIXED_DELTA_TIME
    } else {
        time.delta_seconds()
    };
    for (mut bird, mut transform) in &mut bird_query {
        step_movement(&mut transform.translation, &mut bird.velocity, dt);
    }
}

fn handle_collision(half_extents: Vec2, translation: &Vec3, velocity: &mut Vec3) {
    if (velocity.x > 0. && translation.x + HALF_BIRD_SIZE > half_extents.x)
        || (velocity.x <= 0. && translation.x - HALF_BIRD_SIZE < -half_extents.x)
    {
        velocity.x = -velocity.x;
    }
    let velocity_y = velocity.y;
    if velocity_y < 0. && translation.y - HALF_BIRD_SIZE < -half_extents.y {
        velocity.y = -velocity_y;
    }
    if translation.y + HALF_BIRD_SIZE > half_extents.y && velocity_y > 0.0 {
        velocity.y = 0.0;
    }
}
fn collision_system(windows: Query<&Window>, mut bird_query: Query<(&mut Bird, &Transform)>) {
    let window = windows.single();

    let half_extents = 0.5 * Vec2::new(window.width(), window.height());

    for (mut bird, transform) in &mut bird_query {
        handle_collision(half_extents, &transform.translation, &mut bird.velocity);
    }
}

examples/ui/relative_cursor_position.rs (line 76)

fn relative_cursor_position_system(
    relative_cursor_position_query: Query<&RelativeCursorPosition>,
    mut output_query: Query<&mut Text>,
) {
    let relative_cursor_position = relative_cursor_position_query.single();

    let mut output = output_query.single_mut();

    output.sections[0].value =
        if let Some(relative_cursor_position) = relative_cursor_position.normalized {
            format!(
                "({:.1}, {:.1})",
                relative_cursor_position.x, relative_cursor_position.y
            )
        } else {
            "unknown".to_string()
        };

    output.sections[0].style.color = if relative_cursor_position.mouse_over() {
        Color::rgb(0.1, 0.9, 0.1)
    } else {
        Color::rgb(0.9, 0.1, 0.1)
    };
}

examples/input/text_input.rs (line 186)

fn listen_keyboard_input_events(
    mut commands: Commands,
    mut events: EventReader<KeyboardInput>,
    mut edit_text: Query<(Entity, &mut Text), (Without<Node>, Without<Bubble>)>,
) {
    for event in events.read() {
        match event.key_code {
            KeyCode::Enter => {
                let (entity, text) = edit_text.single();
                commands.entity(entity).insert(Bubble {
                    timer: Timer::from_seconds(5.0, TimerMode::Once),
                });

                commands.spawn(Text2dBundle {
                    text: Text::from_section("".to_string(), text.sections[0].style.clone()),
                    ..default()
                });
            }
            KeyCode::Backspace => {
                edit_text.single_mut().1.sections[0].value.pop();
            }
            _ => continue,
        }
    }
}

Additional examples can be found in:

• examples/2d/rotation.rs
• examples/ecs/parallel_query.rs
• examples/3d/3d_viewport_to_world.rs
• examples/shader/shader_prepass.rs
• examples/3d/tonemapping.rs
• examples/games/contributors.rs
• examples/3d/ssao.rs
• examples/3d/anti_aliasing.rs

pub fn get_single( &self ) -> Result<<<D as QueryData>::ReadOnly as WorldQuery>::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.get_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

• get_single_mut to get the mutable query item.
• single for the panicking version.

Examples found in repository

examples/audio/audio_control.rs (line 27)

fn update_speed(music_controller: Query<&AudioSink, With<MyMusic>>, time: Res<Time>) {
    if let Ok(sink) = music_controller.get_single() {
        sink.set_speed(((time.elapsed_seconds() / 5.0).sin() + 1.0).max(0.1));
    }
}

fn pause(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    music_controller: Query<&AudioSink, With<MyMusic>>,
) {
    if keyboard_input.just_pressed(KeyCode::Space) {
        if let Ok(sink) = music_controller.get_single() {
            sink.toggle();
        }
    }
}

fn volume(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    music_controller: Query<&AudioSink, With<MyMusic>>,
) {
    if let Ok(sink) = music_controller.get_single() {
        if keyboard_input.just_pressed(KeyCode::Equal) {
            sink.set_volume(sink.volume() + 0.1);
        } else if keyboard_input.just_pressed(KeyCode::Minus) {
            sink.set_volume(sink.volume() - 0.1);
        }
    }
}

examples/3d/pbr.rs (line 144)

fn environment_map_load_finish(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    environment_maps: Query<&EnvironmentMapLight>,
    label_query: Query<Entity, With<EnvironmentMapLabel>>,
) {
    if let Ok(environment_map) = environment_maps.get_single() {
        if asset_server.load_state(&environment_map.diffuse_map) == LoadState::Loaded
            && asset_server.load_state(&environment_map.specular_map) == LoadState::Loaded
        {
            if let Ok(label_entity) = label_query.get_single() {
                commands.entity(label_entity).despawn();
            }
        }
    }
}

examples/3d/tonemapping.rs (line 308)

fn drag_drop_image(
    image_mat: Query<&Handle<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.get_single() {
                commands.entity(text_entity).despawn();
            }
        }
    }
}

examples/3d/generate_custom_mesh.rs (line 93)

fn input_handler(
    keyboard_input: Res<ButtonInput<KeyCode>>,
    mesh_query: Query<&Handle<Mesh>, With<CustomUV>>,
    mut meshes: ResMut<Assets<Mesh>>,
    mut query: Query<&mut Transform, With<CustomUV>>,
    time: Res<Time>,
) {
    if keyboard_input.just_pressed(KeyCode::Space) {
        let mesh_handle = mesh_query.get_single().expect("Query not successful");
        let mesh = meshes.get_mut(mesh_handle).unwrap();
        toggle_texture(mesh);
    }
    if keyboard_input.pressed(KeyCode::KeyX) {
        for mut transform in &mut query {
            transform.rotate_x(time.delta_seconds() / 1.2);
        }
    }
    if keyboard_input.pressed(KeyCode::KeyY) {
        for mut transform in &mut query {
            transform.rotate_y(time.delta_seconds() / 1.2);
        }
    }
    if keyboard_input.pressed(KeyCode::KeyZ) {
        for mut transform in &mut query {
            transform.rotate_z(time.delta_seconds() / 1.2);
        }
    }
    if keyboard_input.pressed(KeyCode::KeyR) {
        for mut transform in &mut query {
            transform.look_to(Vec3::NEG_Z, Vec3::Y);
        }
    }
}

pub fn single_mut(&mut self) -> <D as WorldQuery>::Item<'_>

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

Panics

This method panics if the number of query item is not exactly one.

Example

fn regenerate_player_health_system(mut query: Query<&mut Health, With<Player>>) {
    let mut health = query.single_mut();
    health.0 += 1;
}

See also

• get_single_mut for the non-panicking version.
• single to get the read-only query item.

Examples found in repository

examples/games/alien_cake_addict.rs (line 372)

fn scoreboard_system(game: Res<Game>, mut query: Query<&mut Text>) {
    let mut text = query.single_mut();
    text.sections[0].value = format!("Sugar Rush: {}", game.score);
}

examples/window/scale_factor_override.rs (line 70)

fn display_override(mut windows: Query<&mut Window>) {
    let mut window = windows.single_mut();

    window.title = format!(
        "Scale override: {:?}",
        window.resolution.scale_factor_override()
    );
}

/// This system toggles scale factor overrides when enter is pressed
fn toggle_override(input: Res<ButtonInput<KeyCode>>, mut windows: Query<&mut Window>) {
    let mut window = windows.single_mut();

    if input.just_pressed(KeyCode::Enter) {
        let scale_factor_override = window.resolution.scale_factor_override();
        window
            .resolution
            .set_scale_factor_override(scale_factor_override.xor(Some(1.0)));
    }
}

/// This system changes the scale factor override when up or down is pressed
fn change_scale_factor(input: Res<ButtonInput<KeyCode>>, mut windows: Query<&mut Window>) {
    let mut window = windows.single_mut();
    let scale_factor_override = window.resolution.scale_factor_override();
    if input.just_pressed(KeyCode::ArrowUp) {
        window
            .resolution
            .set_scale_factor_override(scale_factor_override.map(|n| n + 1.0));
    } else if input.just_pressed(KeyCode::ArrowDown) {
        window
            .resolution
            .set_scale_factor_override(scale_factor_override.map(|n| (n - 1.0).max(1.0)));
    }
}

examples/3d/3d_gizmos.rs (line 79)

fn rotate_camera(mut query: Query<&mut Transform, With<Camera>>, time: Res<Time>) {
    let mut transform = query.single_mut();

    transform.rotate_around(Vec3::ZERO, Quat::from_rotation_y(time.delta_seconds() / 2.));
}

tests/window/resizing.rs (line 108)

fn sync_dimensions(dim: Res<Dimensions>, mut windows: Query<&mut Window>) {
    if dim.is_changed() {
        let mut window = windows.single_mut();
        window.resolution.set(dim.width as f32, dim.height as f32);
    }
}

tests/window/minimising.rs (line 23)

fn minimise_automatically(mut windows: Query<&mut Window>, mut frames: Local<u32>) {
    if *frames == 60 {
        let mut window = windows.single_mut();
        window.set_minimized(true);
    } else {
        *frames += 1;
    }
}

examples/stress_tests/many_lights.rs (line 136)

fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
    let mut camera_transform = camera_query.single_mut();
    let delta = time.delta_seconds() * 0.15;
    camera_transform.rotate_z(delta);
    camera_transform.rotate_x(delta);
}

Additional examples can be found in:

• examples/ui/window_fallthrough.rs
• examples/stress_tests/many_sprites.rs
• examples/shader/shader_material_screenspace_texture.rs
• examples/stress_tests/many_animated_sprites.rs
• examples/ecs/iter_combinations.rs
• examples/stress_tests/many_cubes.rs
• examples/2d/pixel_grid_snap.rs
• examples/3d/atmospheric_fog.rs
• examples/window/window_settings.rs
• examples/3d/spotlight.rs
• examples/input/text_input.rs
• examples/input/mouse_grab.rs
• examples/stress_tests/many_gizmos.rs
• examples/2d/bounding_2d.rs
• examples/window/window_resizing.rs
• examples/window/low_power.rs
• examples/audio/spatial_audio_3d.rs
• examples/audio/spatial_audio_2d.rs
• examples/stress_tests/bevymark.rs
• examples/ui/relative_cursor_position.rs
• examples/math/render_primitives.rs
• examples/3d/deterministic.rs
• examples/3d/shadow_biases.rs
• examples/games/game_menu.rs
• examples/games/breakout.rs
• examples/shader/shader_prepass.rs
• examples/3d/parallax_mapping.rs
• examples/3d/tonemapping.rs
• examples/games/contributors.rs
• examples/games/stepping.rs
• examples/3d/wireframe.rs
• examples/3d/lighting.rs
• examples/3d/split_screen.rs
• examples/2d/rotation.rs
• examples/3d/blend_modes.rs
• examples/3d/anti_aliasing.rs
• examples/ui/size_constraints.rs
• examples/3d/ssao.rs
• examples/3d/deferred_rendering.rs
• examples/3d/bloom_3d.rs
• examples/2d/bloom_2d.rs
• examples/3d/fog.rs
• examples/3d/transmission.rs

pub fn get_single_mut( &mut self ) -> Result<<D as WorldQuery>::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.get_single_mut().expect("Error: Could not find a single player.");
    health.0 += 1;
}

See also

• get_single to get the read-only query item.
• single_mut for the panicking version.

Examples found in repository

examples/3d/../helpers/camera_controller.rs (line 110)

fn run_camera_controller(
    time: Res<Time>,
    mut windows: Query<&mut Window>,
    mut mouse_events: EventReader<MouseMotion>,
    mouse_button_input: Res<ButtonInput<MouseButton>>,
    key_input: Res<ButtonInput<KeyCode>>,
    mut toggle_cursor_grab: Local<bool>,
    mut mouse_cursor_grab: Local<bool>,
    mut query: Query<(&mut Transform, &mut CameraController), With<Camera>>,
) {
    let dt = time.delta_seconds();

    if let Ok((mut transform, mut controller)) = query.get_single_mut() {
        if !controller.initialized {
            let (yaw, pitch, _roll) = transform.rotation.to_euler(EulerRot::YXZ);
            controller.yaw = yaw;
            controller.pitch = pitch;
            controller.initialized = true;
            info!("{}", *controller);
        }
        if !controller.enabled {
            mouse_events.clear();
            return;
        }

        // Handle key input
        let mut axis_input = Vec3::ZERO;
        if key_input.pressed(controller.key_forward) {
            axis_input.z += 1.0;
        }
        if key_input.pressed(controller.key_back) {
            axis_input.z -= 1.0;
        }
        if key_input.pressed(controller.key_right) {
            axis_input.x += 1.0;
        }
        if key_input.pressed(controller.key_left) {
            axis_input.x -= 1.0;
        }
        if key_input.pressed(controller.key_up) {
            axis_input.y += 1.0;
        }
        if key_input.pressed(controller.key_down) {
            axis_input.y -= 1.0;
        }

        let mut cursor_grab_change = false;
        if key_input.just_pressed(controller.keyboard_key_toggle_cursor_grab) {
            *toggle_cursor_grab = !*toggle_cursor_grab;
            cursor_grab_change = true;
        }
        if mouse_button_input.just_pressed(controller.mouse_key_cursor_grab) {
            *mouse_cursor_grab = true;
            cursor_grab_change = true;
        }
        if mouse_button_input.just_released(controller.mouse_key_cursor_grab) {
            *mouse_cursor_grab = false;
            cursor_grab_change = true;
        }
        let cursor_grab = *mouse_cursor_grab || *toggle_cursor_grab;

        // Apply movement update
        if axis_input != Vec3::ZERO {
            let max_speed = if key_input.pressed(controller.key_run) {
                controller.run_speed
            } else {
                controller.walk_speed
            };
            controller.velocity = axis_input.normalize() * max_speed;
        } else {
            let friction = controller.friction.clamp(0.0, 1.0);
            controller.velocity *= 1.0 - friction;
            if controller.velocity.length_squared() < 1e-6 {
                controller.velocity = Vec3::ZERO;
            }
        }
        let forward = *transform.forward();
        let right = *transform.right();
        transform.translation += controller.velocity.x * dt * right
            + controller.velocity.y * dt * Vec3::Y
            + controller.velocity.z * dt * forward;

        // Handle cursor grab
        if cursor_grab_change {
            if cursor_grab {
                for mut window in &mut windows {
                    if !window.focused {
                        continue;
                    }

                    window.cursor.grab_mode = CursorGrabMode::Locked;
                    window.cursor.visible = false;
                }
            } else {
                for mut window in &mut windows {
                    window.cursor.grab_mode = CursorGrabMode::None;
                    window.cursor.visible = true;
                }
            }
        }

        // Handle mouse input
        let mut mouse_delta = Vec2::ZERO;
        if cursor_grab {
            for mouse_event in mouse_events.read() {
                mouse_delta += mouse_event.delta;
            }
        } else {
            mouse_events.clear();
        }

        if mouse_delta != Vec2::ZERO {
            // Apply look update
            controller.pitch = (controller.pitch
                - mouse_delta.y * RADIANS_PER_DOT * controller.sensitivity)
                .clamp(-PI / 2., PI / 2.);
            controller.yaw -= mouse_delta.x * RADIANS_PER_DOT * controller.sensitivity;
            transform.rotation =
                Quat::from_euler(EulerRot::ZYX, 0.0, controller.yaw, controller.pitch);
        }
    }
}

pub fn is_empty(&self) -> bool

Returns true if there are no query items.

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/games/stepping.rs (line 238)

fn update_ui(
    mut commands: Commands,
    state: Res<State>,
    stepping: Res<Stepping>,
    mut ui: Query<(Entity, &mut Text, &Visibility), With<SteppingUi>>,
) {
    if ui.is_empty() {
        return;
    }

    // ensure the UI is only visible when stepping is enabled
    let (ui, mut text, vis) = ui.single_mut();
    match (vis, stepping.is_enabled()) {
        (Visibility::Hidden, true) => {
            commands.entity(ui).insert(Visibility::Inherited);
        }
        (Visibility::Hidden, false) | (_, true) => (),
        (_, false) => {
            commands.entity(ui).insert(Visibility::Hidden);
        }
    }

    // if we're not stepping, there's nothing more to be done here.
    if !stepping.is_enabled() {
        return;
    }

    let (cursor_schedule, cursor_system) = match stepping.cursor() {
        // no cursor means stepping isn't enabled, so we're done here
        None => return,
        Some(c) => c,
    };

    for (schedule, system, text_index) in &state.systems {
        let mark = if &cursor_schedule == schedule && *system == cursor_system {
            "-> "
        } else {
            "   "
        };
        text.sections[*text_index].value = mark.to_string();
    }
}

examples/3d/irradiance_volumes.rs (line 567)

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::RED),
            extension: VoxelVisualizationExtension {
                irradiance_volume_info: VoxelVisualizationIrradianceVolumeInfo {
                    transform: VOXEL_TRANSFORM.inverse(),
                    inverse_transform: VOXEL_TRANSFORM,
                    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(MaterialMeshBundle {
                            mesh: example_assets.voxel_cube.clone(),
                            material: voxel_cube_material.clone(),
                            transform: Transform::from_scale(Vec3::splat(VOXEL_CUBE_SCALE))
                                .with_translation(pos),
                            ..default()
                        })
                        .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.

Example

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

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 Q

Example

fn reusable_function(lens: &mut QueryLens<&A>) {
    assert_eq!(lens.query().single().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 paramters.

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

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

Gets a QueryLens with the same accesses as the existing query

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

where D: ReadOnlyQueryData, F: QueryFilter,

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

Returns the query item for the given Entity, with the actual “inner” world lifetime.

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

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

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);
    }
}

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> 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<'w, 's, Q, F>

where Q: QueryData, F: QueryFilter,

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

Converts to this type from the input type.

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

where D: QueryData, F: QueryFilter,

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

where <D as QueryData>::ReadOnly: WorldQuery<Item<'w> = &'w Children>,

Returns an Iterator of Entitys over all of entitys descendants.

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

where <D as QueryData>::ReadOnly: WorldQuery<Item<'w> = &'w Parent>,

Returns an Iterator of Entitys over all of entitys ancestors.

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

where D: QueryData, F: QueryFilter,

type Item = <<D as QueryData>::ReadOnly as WorldQuery>::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 WorldQuery>::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<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.

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).

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 apply_deferred.

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

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