ray_casting3.rs

use bevy::prelude::*;
use bevy::window::PrimaryWindow;
use bevy_rapier3d::prelude::*;

fn main() {
    App::new()
        .insert_resource(ClearColor(Color::rgb(
            0xF9 as f32 / 255.0,
            0xF9 as f32 / 255.0,
            0xFF as f32 / 255.0,
        )))
        .add_plugins((
            DefaultPlugins,
            RapierPhysicsPlugin::<NoUserData>::default(),
            RapierDebugRenderPlugin::default(),
        ))
        .add_systems(Startup, (setup_graphics, setup_physics))
        .add_systems(Update, cast_ray)
        .run();
}

pub fn setup_graphics(mut commands: Commands) {
    commands.spawn(Camera3dBundle {
        transform: Transform::from_xyz(-30.0, 30.0, 100.0)
            .looking_at(Vec3::new(0.0, 10.0, 0.0), Vec3::Y),
        ..Default::default()
    });
}

pub fn setup_physics(mut commands: Commands) {
    /*
     * Ground
     */
    let ground_size = 200.1;
    let ground_height = 0.1;

    commands.spawn((
        TransformBundle::from(Transform::from_xyz(0.0, -ground_height, 0.0)),
        Collider::cuboid(ground_size, ground_height, ground_size),
    ));

    /*
     * Create the cubes
     */
    let num = 8;
    let rad = 1.0;

    let shift = rad * 2.0 + rad;
    let centerx = shift * (num / 2) as f32;
    let centery = shift / 2.0;
    let centerz = shift * (num / 2) as f32;

    let mut offset = -(num as f32) * (rad * 2.0 + rad) * 0.5;

    for j in 0usize..20 {
        for i in 0..num {
            for k in 0usize..num {
                let x = i as f32 * shift - centerx + offset;
                let y = j as f32 * shift + centery + 3.0;
                let z = k as f32 * shift - centerz + offset;

                // Build the rigid body.
                commands.spawn((
                    TransformBundle::from(Transform::from_xyz(x, y, z)),
                    RigidBody::Dynamic,
                    Collider::cuboid(rad, rad, rad),
                ));
            }
        }

        offset -= 0.05 * rad * (num as f32 - 1.0);
    }
}

pub fn cast_ray(
    mut commands: Commands,
    windows: Query<&Window, With<PrimaryWindow>>,
    rapier_context: Res<RapierContext>,
    cameras: Query<(&Camera, &GlobalTransform)>,
) {
    let window = windows.single();

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

    // We will color in read the colliders hovered by the mouse.
    for (camera, camera_transform) in &cameras {
        // First, compute a ray from the mouse position.
        let Some(ray) = camera.viewport_to_world(camera_transform, cursor_position) else {
            return;
        };

        // Then cast the ray.
        let hit = rapier_context
            .cast_ray(
                DEFAULT_WORLD_ID,
                ray.origin,
                *ray.direction,
                f32::MAX,
                true,
                QueryFilter::only_dynamic(),
            )
            .expect("Default world should exist.");

        if let Some((entity, _toi)) = hit {
            // Color in blue the entity we just hit.
            // Because of the query filter, only colliders attached to a dynamic body
            // will get an event.
            let color = Color::BLUE;
            commands.entity(entity).insert(ColliderDebugColor(color));
        }
    }
}