mesh_ray_cast/
mesh_ray_cast.rs

1//! Demonstrates how to use the [`MeshRayCast`] system parameter to chain multiple ray casts
2//! and bounce off of surfaces.
3
4use std::f32::consts::{FRAC_PI_2, PI};
5
6use bevy::{
7    color::palettes::css, core_pipeline::tonemapping::Tonemapping, math::vec3,
8    picking::backend::ray::RayMap, post_process::bloom::Bloom, prelude::*,
9};
10
11fn main() {
12    App::new()
13        .add_plugins(DefaultPlugins)
14        .add_systems(Startup, setup)
15        .add_systems(Update, bouncing_raycast)
16        .insert_resource(ClearColor(Color::BLACK))
17        .run();
18}
19
20const MAX_BOUNCES: usize = 64;
21const LASER_SPEED: f32 = 0.03;
22
23fn bouncing_raycast(
24    mut ray_cast: MeshRayCast,
25    mut gizmos: Gizmos,
26    time: Res<Time>,
27    // The ray map stores rays cast by the cursor
28    ray_map: Res<RayMap>,
29) {
30    // Cast an automatically moving ray and bounce it off of surfaces
31    let t = ops::cos((time.elapsed_secs() - 4.0).max(0.0) * LASER_SPEED) * PI;
32    let ray_pos = Vec3::new(ops::sin(t), ops::cos(3.0 * t) * 0.5, ops::cos(t)) * 0.5;
33    let ray_dir = Dir3::new(-ray_pos).unwrap();
34    let ray = Ray3d::new(ray_pos, ray_dir);
35    gizmos.sphere(ray_pos, 0.1, Color::WHITE);
36    bounce_ray(ray, &mut ray_cast, &mut gizmos, Color::from(css::RED));
37
38    // Cast a ray from the cursor and bounce it off of surfaces
39    for (_, ray) in ray_map.iter() {
40        bounce_ray(*ray, &mut ray_cast, &mut gizmos, Color::from(css::GREEN));
41    }
42}
43
44// Bounces a ray off of surfaces `MAX_BOUNCES` times.
45fn bounce_ray(mut ray: Ray3d, ray_cast: &mut MeshRayCast, gizmos: &mut Gizmos, color: Color) {
46    let mut intersections = Vec::with_capacity(MAX_BOUNCES + 1);
47    intersections.push((ray.origin, Color::srgb(30.0, 0.0, 0.0)));
48
49    for i in 0..MAX_BOUNCES {
50        // Cast the ray and get the first hit
51        let Some((_, hit)) = ray_cast
52            .cast_ray(ray, &MeshRayCastSettings::default())
53            .first()
54        else {
55            break;
56        };
57
58        // Draw the point of intersection and add it to the list
59        let brightness = 1.0 + 10.0 * (1.0 - i as f32 / MAX_BOUNCES as f32);
60        intersections.push((hit.point, Color::BLACK.mix(&color, brightness)));
61        gizmos.sphere(hit.point, 0.005, Color::BLACK.mix(&color, brightness * 2.0));
62
63        // Reflect the ray off of the surface
64        ray.direction = Dir3::new(ray.direction.reflect(hit.normal)).unwrap();
65        ray.origin = hit.point + ray.direction * 1e-6;
66    }
67    gizmos.linestrip_gradient(intersections);
68}
69
70// Set up a simple 3D scene
71fn setup(
72    mut commands: Commands,
73    mut meshes: ResMut<Assets<Mesh>>,
74    mut materials: ResMut<Assets<StandardMaterial>>,
75) {
76    // Make a box of planes facing inward so the laser gets trapped inside
77    let plane_mesh = meshes.add(Plane3d::default());
78    let plane_material = materials.add(Color::from(css::GRAY).with_alpha(0.01));
79    let create_plane = move |translation, rotation| {
80        (
81            Transform::from_translation(translation)
82                .with_rotation(Quat::from_scaled_axis(rotation)),
83            Mesh3d(plane_mesh.clone()),
84            MeshMaterial3d(plane_material.clone()),
85        )
86    };
87
88    commands.spawn(create_plane(vec3(0.0, 0.5, 0.0), Vec3::X * PI));
89    commands.spawn(create_plane(vec3(0.0, -0.5, 0.0), Vec3::ZERO));
90    commands.spawn(create_plane(vec3(0.5, 0.0, 0.0), Vec3::Z * FRAC_PI_2));
91    commands.spawn(create_plane(vec3(-0.5, 0.0, 0.0), Vec3::Z * -FRAC_PI_2));
92    commands.spawn(create_plane(vec3(0.0, 0.0, 0.5), Vec3::X * -FRAC_PI_2));
93    commands.spawn(create_plane(vec3(0.0, 0.0, -0.5), Vec3::X * FRAC_PI_2));
94
95    // Light
96    commands.spawn((
97        DirectionalLight::default(),
98        Transform::from_rotation(Quat::from_euler(EulerRot::XYZ, -0.1, 0.2, 0.0)),
99    ));
100
101    // Camera
102    commands.spawn((
103        Camera3d::default(),
104        Transform::from_xyz(1.5, 1.5, 1.5).looking_at(Vec3::ZERO, Vec3::Y),
105        Tonemapping::TonyMcMapface,
106        Bloom::default(),
107    ));
108}
mesh_ray_cast/mesh_ray_cast.rs

mesh_ray_cast/
mesh_ray_cast.rs
