c5e89894f4
# Objective Fixes #3183. Requiring a `&TaskPool` parameter is sort of meaningless if the only correct one is to use the one provided by `Res<ComputeTaskPool>` all the time. ## Solution Have `QueryState` save a clone of the `ComputeTaskPool` which is used for all `par_for_each` functions. ~~Adds a small overhead of the internal `Arc` clone as a part of the startup, but the ergonomics win should be well worth this hardly-noticable overhead.~~ Updated the docs to note that it will panic the task pool is not present as a resource. # Future Work If https://github.com/bevyengine/rfcs/pull/54 is approved, we can replace these resource lookups with a static function call instead to get the `ComputeTaskPool`. --- ## Changelog Removed: The `task_pool` parameter of `Query(State)::par_for_each(_mut)`. These calls will use the `World`'s `ComputeTaskPool` resource instead. ## Migration Guide The `task_pool` parameter for `Query(State)::par_for_each(_mut)` has been removed. Remove these parameters from all calls to these functions. Before: ```rust fn parallel_system( task_pool: Res<ComputeTaskPool>, query: Query<&MyComponent>, ) { query.par_for_each(&task_pool, 32, |comp| { ... }); } ``` After: ```rust fn parallel_system(query: Query<&MyComponent>) { query.par_for_each(32, |comp| { ... }); } ``` If using `Query(State)` outside of a system run by the scheduler, you may need to manually configure and initialize a `ComputeTaskPool` as a resource in the `World`.
72 lines
2.5 KiB
Rust
72 lines
2.5 KiB
Rust
//! Illustrates parallel queries with `ParallelIterator`.
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use bevy::prelude::*;
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use rand::random;
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#[derive(Component, Deref)]
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struct Velocity(Vec2);
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fn spawn_system(mut commands: Commands, asset_server: Res<AssetServer>) {
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commands.spawn_bundle(OrthographicCameraBundle::new_2d());
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let texture = asset_server.load("branding/icon.png");
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for _ in 0..128 {
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commands
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.spawn_bundle(SpriteBundle {
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texture: texture.clone(),
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transform: Transform::from_scale(Vec3::splat(0.1)),
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..default()
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})
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.insert(Velocity(
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20.0 * Vec2::new(random::<f32>() - 0.5, random::<f32>() - 0.5),
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));
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}
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}
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// Move sprites according to their velocity
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fn move_system(mut sprites: Query<(&mut Transform, &Velocity)>) {
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// Compute the new location of each sprite in parallel on the
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// ComputeTaskPool using batches of 32 sprites
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//
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// This example is only for demonstrative purposes. Using a
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// ParallelIterator for an inexpensive operation like addition on only 128
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// elements will not typically be faster than just using a normal Iterator.
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// See the ParallelIterator documentation for more information on when
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// to use or not use ParallelIterator over a normal Iterator.
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sprites.par_for_each_mut(32, |(mut transform, velocity)| {
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transform.translation += velocity.extend(0.0);
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});
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}
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// Bounce sprites outside the window
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fn bounce_system(windows: Res<Windows>, mut sprites: Query<(&Transform, &mut Velocity)>) {
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let window = windows.primary();
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let width = window.width();
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let height = window.height();
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let left = width / -2.0;
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let right = width / 2.0;
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let bottom = height / -2.0;
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let top = height / 2.0;
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sprites
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// Batch size of 32 is chosen to limit the overhead of
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// ParallelIterator, since negating a vector is very inexpensive.
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.par_for_each_mut(32, |(transform, mut v)| {
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if !(left < transform.translation.x
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&& transform.translation.x < right
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&& bottom < transform.translation.y
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&& transform.translation.y < top)
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{
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// For simplicity, just reverse the velocity; don't use realistic bounces
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v.0 = -v.0;
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}
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});
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}
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_startup_system(spawn_system)
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.add_system(move_system)
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.add_system(bounce_system)
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.run();
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}
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