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parallel_query.rs
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parallel_query.rs
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use bevy::{prelude::*, tasks::prelude::*};
use rand::random;
struct Velocity(Vec2);
fn spawn_system(
mut commands: Commands,
asset_server: Res<AssetServer>,
mut materials: ResMut<Assets<ColorMaterial>>,
) {
commands.spawn(OrthographicCameraBundle::new_2d());
let texture_handle = asset_server.load("branding/icon.png");
let material = materials.add(texture_handle.into());
for _ in 0..128 {
commands
.spawn(SpriteBundle {
material: material.clone(),
transform: Transform::from_scale(Vec3::splat(0.1)),
..Default::default()
})
.with(Velocity(
20.0 * Vec2::new(random::<f32>() - 0.5, random::<f32>() - 0.5),
));
}
}
// Move sprites according to their velocity
fn move_system(pool: Res<ComputeTaskPool>, mut sprites: Query<(&mut Transform, &Velocity)>) {
// Compute the new location of each sprite in parallel on the
// ComputeTaskPool using batches of 32 sprites
//
// This example is only for demonstrative purposes. Using a
// ParallelIterator for an inexpensive operation like addition on only 128
// elements will not typically be faster than just using a normal Iterator.
// See the ParallelIterator documentation for more information on when
// to use or not use ParallelIterator over a normal Iterator.
sprites.par_for_each_mut(&pool, 32, |(mut transform, velocity)| {
transform.translation += velocity.0.extend(0.0);
});
}
// Bounce sprites outside the window
fn bounce_system(
pool: Res<ComputeTaskPool>,
windows: Res<Windows>,
mut sprites: Query<(&Transform, &mut Velocity)>,
) {
let window = windows.get_primary().expect("No primary window.");
let width = window.width();
let height = window.height();
let left = width / -2.0;
let right = width / 2.0;
let bottom = height / -2.0;
let top = height / 2.0;
sprites
// Batch size of 32 is chosen to limit the overhead of
// ParallelIterator, since negating a vector is very inexpensive.
.par_for_each_mut(&pool, 32, |(transform, mut v)| {
if !(left < transform.translation.x
&& transform.translation.x < right
&& bottom < transform.translation.y
&& transform.translation.y < top)
{
// For simplicity, just reverse the velocity; don't use realistic bounces
v.0 = -v.0;
}
});
}
fn main() {
App::build()
.add_plugins(DefaultPlugins)
.add_startup_system(spawn_system.system())
.add_system(move_system.system())
.add_system(bounce_system.system())
.run();
}