Support Warning
WebGPU is currently only supported on Chrome starting with version 113, and only on desktop. If they don't work on your configuration, you can check the WebGL2 examples here.iter_combinations.rs:
//! Shows how to iterate over combinations of query results.
use bevy::{color::palettes::css::ORANGE_RED, math::FloatPow, prelude::*};
use rand::{Rng, SeedableRng};
use rand_chacha::ChaCha8Rng;
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.insert_resource(ClearColor(Color::BLACK))
.add_systems(Startup, generate_bodies)
.add_systems(FixedUpdate, (interact_bodies, integrate))
.add_systems(Update, look_at_star)
.run();
}
const GRAVITY_CONSTANT: f32 = 0.001;
const NUM_BODIES: usize = 100;
#[derive(Component, Default)]
struct Mass(f32);
#[derive(Component, Default)]
struct Acceleration(Vec3);
#[derive(Component, Default)]
struct LastPos(Vec3);
#[derive(Component)]
struct Star;
#[derive(Bundle, Default)]
struct BodyBundle {
mesh: Mesh3d,
material: MeshMaterial3d<StandardMaterial>,
mass: Mass,
last_pos: LastPos,
acceleration: Acceleration,
}
fn generate_bodies(
time: Res<Time<Fixed>>,
mut commands: Commands,
mut meshes: ResMut<Assets<Mesh>>,
mut materials: ResMut<Assets<StandardMaterial>>,
) {
let mesh = meshes.add(Sphere::new(1.0).mesh().ico(3).unwrap());
let color_range = 0.5..1.0;
let vel_range = -0.5..0.5;
// We're seeding the PRNG here to make this example deterministic for testing purposes.
// This isn't strictly required in practical use unless you need your app to be deterministic.
let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
for _ in 0..NUM_BODIES {
let radius: f32 = rng.gen_range(0.1..0.7);
let mass_value = FloatPow::cubed(radius) * 10.;
let position = Vec3::new(
rng.gen_range(-1.0..1.0),
rng.gen_range(-1.0..1.0),
rng.gen_range(-1.0..1.0),
)
.normalize()
* ops::cbrt(rng.gen_range(0.2f32..1.0))
* 15.;
commands.spawn((
BodyBundle {
mesh: Mesh3d(mesh.clone()),
material: MeshMaterial3d(materials.add(Color::srgb(
rng.gen_range(color_range.clone()),
rng.gen_range(color_range.clone()),
rng.gen_range(color_range.clone()),
))),
mass: Mass(mass_value),
acceleration: Acceleration(Vec3::ZERO),
last_pos: LastPos(
position
- Vec3::new(
rng.gen_range(vel_range.clone()),
rng.gen_range(vel_range.clone()),
rng.gen_range(vel_range.clone()),
) * time.timestep().as_secs_f32(),
),
},
Transform {
translation: position,
scale: Vec3::splat(radius),
..default()
},
));
}
// add bigger "star" body in the center
let star_radius = 1.;
commands
.spawn((
BodyBundle {
mesh: Mesh3d(meshes.add(Sphere::new(1.0).mesh().ico(5).unwrap())),
material: MeshMaterial3d(materials.add(StandardMaterial {
base_color: ORANGE_RED.into(),
emissive: LinearRgba::from(ORANGE_RED) * 2.,
..default()
})),
mass: Mass(500.0),
..default()
},
Transform::from_scale(Vec3::splat(star_radius)),
Star,
))
.with_child(PointLight {
color: Color::WHITE,
range: 100.0,
radius: star_radius,
..default()
});
commands.spawn((
Camera3d::default(),
Transform::from_xyz(0.0, 10.5, -30.0).looking_at(Vec3::ZERO, Vec3::Y),
));
}
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;
}
}
fn integrate(time: Res<Time>, mut query: Query<(&mut Acceleration, &mut Transform, &mut LastPos)>) {
let dt_sq = time.delta_secs() * time.delta_secs();
for (mut acceleration, mut transform, mut last_pos) in &mut query {
// verlet integration
// x(t+dt) = 2x(t) - x(t-dt) + a(t)dt^2 + O(dt^4)
let new_pos = transform.translation * 2.0 - last_pos.0 + acceleration.0 * dt_sq;
acceleration.0 = Vec3::ZERO;
last_pos.0 = transform.translation;
transform.translation = new_pos;
}
}
fn look_at_star(
mut camera: Single<&mut Transform, (With<Camera>, Without<Star>)>,
star: Single<&Transform, With<Star>>,
) {
let new_rotation = camera
.looking_at(star.translation, Vec3::Y)
.rotation
.lerp(camera.rotation, 0.1);
camera.rotation = new_rotation;
}