Bevy spatial queries

When to use

Load this when a design needs line of sight, a volume overlap, a ground probe, or a mouse pick. Screen-to-2D-world mapping that does not hit a collider is a camera helper, not a physics query.

ECS shape

• Components own a probe radius or a facing marker. Positions come from GlobalTransform.
• Camera pick: Camera::viewport_to_world_2d with GlobalTransform maps a cursor to a 2D world point. That is a camera map, then a distance test against sprites. See bevy-camera-systems.
• Systems read transforms after movement. Chain the probe after the system that writes Transform when both run in the same schedule.

Probe choice

Need	Bevy path
Collider cast or sweep	bevy-physics-2d or bevy-physics-3d. This skill measures distance and facing with Transform.
Pointer in the 2D world	viewport_to_world_2d, then the nearest entity inside a radius.
Exclude the caster	Skip the probe Entity when comparing distances.
View cone	Dot the view forward with the direction to the target and compare against a cosine threshold.

Scope

• Stock Bevy measures points, radii, and facing. Collider casts, sweeps, and normals stay on bevy-physics-2d and bevy-physics-3d.
• A probe never reports itself. Compare Entity before accepting a hit.
• Chain the probe after movement so it reads the transforms written this frame.

Examples

[dependencies]
bevy = "0.20"

Map the cursor into the world, then keep the closest marker inside the pick radius.

#[derive(Component)]
struct Pickable;

use bevy::window::PrimaryWindow;

fn pick_nearest(
    windows: Query<&Window, With<PrimaryWindow>>,
    cameras: Query<(&Camera, &GlobalTransform), With<Camera2d>>,
    targets: Query<(Entity, &GlobalTransform), With<Pickable>>,
) {
    let Ok(window) = windows.single() else {
        return;
    };
    let Ok((camera, camera_tf)) = cameras.single() else {
        return;
    };
    let Some(cursor) = window.cursor_position() else {
        return;
    };
    let Ok(world) = camera.viewport_to_world_2d(camera_tf, cursor) else {
        return;
    };
    let mut best: Option<(Entity, f32)> = None;
    for (entity, transform) in &targets {
        let point = transform.translation().truncate();
        let distance = point.distance(world);
        if distance > 24.0 {
            continue;
        }
        if best.is_none_or(|(_, so_far)| distance < so_far) {
            best = Some((entity, distance));
        }
    }
    let _hit = best.map(|(entity, _)| entity);
}

A radius probe lists other entities inside its range and skips its own entity.

#[derive(Component)]
struct Probe {
    radius: f32,
}

#[derive(Component)]
struct Body;

fn overlaps(
    probes: Query<(Entity, &GlobalTransform, &Probe)>,
    bodies: Query<(Entity, &GlobalTransform), With<Body>>,
) {
    for (probe_entity, probe_tf, probe) in &probes {
        for (body, body_tf) in &bodies {
            if body == probe_entity {
                continue;
            }
            let distance = probe_tf.translation().distance(body_tf.translation());
            if distance <= probe.radius {
                let _hit = body;
            }
        }
    }
}

Facing uses the view forward and a cosine limit. Movement writes Transform first. The sight test reads Transform in the next chained system, because GlobalTransform updates only after propagation.

#[derive(Component)]
struct Watcher {
    cos_limit: f32,
}

#[derive(Component)]
struct Mark;

fn advance(mut watchers: Query<&mut Transform, With<Watcher>>) {
    for mut transform in &mut watchers {
        transform.translation.x += 1.0;
    }
}

fn can_see(
    watchers: Query<(&Transform, &Watcher)>,
    marks: Query<&Transform, (With<Mark>, Without<Watcher>)>,
) {
    for (watcher_tf, watcher) in &watchers {
        let origin = watcher_tf.translation;
        let forward = watcher_tf.forward().as_vec3();
        for mark_tf in &marks {
            let to = mark_tf.translation - origin;
            let length = to.length();
            if length <= f32::EPSILON {
                continue;
            }
            let facing = forward.dot(to / length);
            if facing >= watcher.cos_limit {
                let _seen = true;
            }
        }
    }
}

pub struct SpatialPlugin;

impl Plugin for SpatialPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Update, (advance, can_see).chain());
    }
}

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	Component	One system via Query	Update or FixedMain
One value for the whole app	Resource	One system	Startup to insert, then the schedule that reads it
Spawn	Commands	The spawning system	Startup for the initial world; later schedules for runtime spawn
Order that must not race	.chain()	The chained systems only	Same schedule
Plugin boundary	Plugin	build registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	Component + Query	A field stored outside the world
App-wide config or clock	Resource	Copy the value onto every entity
Stable simulation step	FixedMain and the Fixed clock	Tie simulation to raw frame Update
Startup spawn	Commands in Startup	Spawn from a render system
Same-frame facing	advance then can_see with .chain() on Transform	Reading GlobalTransform in the system that just wrote Transform
Collider cast	bevy-physics-2d or bevy-physics-3d	An invented ray or mask API
Cross-system notice that is not shared state	Message or observer slot in bevy-events-messaging	A new event type invented in this file
An API outside the documented set	Check the official documentation	A made-up crate or API

Load references/ecs-ownership.md for the ownership table.

NEVER

• Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.

• Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• Do not read GlobalTransform in the same system that just wrote Transform. WHY: propagation has not run, so the global pose is still last frame.

• No Avian, Rapier, or any other named physics crate as the chosen solver. WHY: collider casts stay on the physics skills; this skill uses transforms.

• No invented intersect_ray or mask APIs. WHY: stock Bevy here is distance, radius, and a dot product.

Reference

Official links stay on unversioned latest pages. The library pin on bevy-master stays 0.20.0. No stock spatial-query module is used here.

Official Documentation

• Assets - Official asset catalog. No query plugin was selected.
• Examples - Example tree on the latest branch.
• ECS - Systems, Query, and .chain().
• Quick Start: plugins - add_plugins without a chosen physics crate. viewport_to_world_2d is a camera map; details live on bevy-camera-systems.

Related Skills

Prerequisites

• bevy-master - ECS ownership.
• bevy-camera-systems - Viewport to 2D world, without a hit test.

Complements

• bevy-physics-2d - 2D physics and solver choice.
• bevy-physics-3d - 3D physics and solver choice.
• godot-raycasting-queries - Godot package for cast queries.

Downstream / consumers

• bevy-ai-navigation - Sensors that need a cast.

Master

• bevy-master - Bevy router.