parallel_query/
parallel_query.rs

1//! Illustrates parallel queries with `ParallelIterator`.
2
3use bevy::{ecs::batching::BatchingStrategy, prelude::*};
4use rand::{Rng, SeedableRng};
5use rand_chacha::ChaCha8Rng;
6
7#[derive(Component, Deref)]
8struct Velocity(Vec2);
9
10fn spawn_system(mut commands: Commands, asset_server: Res<AssetServer>) {
11    commands.spawn(Camera2d);
12    let texture = asset_server.load("branding/icon.png");
13
14    // We're seeding the PRNG here to make this example deterministic for testing purposes.
15    // This isn't strictly required in practical use unless you need your app to be deterministic.
16    let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
17    for z in 0..128 {
18        commands.spawn((
19            Sprite::from_image(texture.clone()),
20            Transform::from_scale(Vec3::splat(0.1))
21                .with_translation(Vec2::splat(0.0).extend(z as f32)),
22            Velocity(20.0 * Vec2::new(rng.r#gen::<f32>() - 0.5, rng.r#gen::<f32>() - 0.5)),
23        ));
24    }
25}
26
27// Move sprites according to their velocity
28fn move_system(mut sprites: Query<(&mut Transform, &Velocity)>) {
29    // Compute the new location of each sprite in parallel on the
30    // ComputeTaskPool
31    //
32    // This example is only for demonstrative purposes. Using a
33    // ParallelIterator for an inexpensive operation like addition on only 128
34    // elements will not typically be faster than just using a normal Iterator.
35    // See the ParallelIterator documentation for more information on when
36    // to use or not use ParallelIterator over a normal Iterator.
37    sprites
38        .par_iter_mut()
39        .for_each(|(mut transform, velocity)| {
40            transform.translation += velocity.extend(0.0);
41        });
42}
43
44// Bounce sprites outside the window
45fn bounce_system(window: Query<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
46    let Ok(window) = window.single() else {
47        return;
48    };
49    let width = window.width();
50    let height = window.height();
51    let left = width / -2.0;
52    let right = width / 2.0;
53    let bottom = height / -2.0;
54    let top = height / 2.0;
55    // The default batch size can also be overridden.
56    // In this case a batch size of 32 is chosen to limit the overhead of
57    // ParallelIterator, since negating a vector is very inexpensive.
58    sprites
59        .par_iter_mut()
60        .batching_strategy(BatchingStrategy::fixed(32))
61        .for_each(|(transform, mut v)| {
62            if !(left < transform.translation.x
63                && transform.translation.x < right
64                && bottom < transform.translation.y
65                && transform.translation.y < top)
66            {
67                // For simplicity, just reverse the velocity; don't use realistic bounces
68                v.0 = -v.0;
69            }
70        });
71}
72
73fn main() {
74    App::new()
75        .add_plugins(DefaultPlugins)
76        .add_systems(Startup, spawn_system)
77        .add_systems(Update, (move_system, bounce_system))
78        .run();
79}
parallel_query/parallel_query.rs

parallel_query/
parallel_query.rs
