2ad5908e58
# Objective As discussed in #14275, Bevy is currently too prone to panic, and makes the easy / beginner-friendly way to do a large number of operations just to panic on failure. This is seriously frustrating in library code, but also slows down development, as many of the `Query::single` panics can actually safely be an early return (these panics are often due to a small ordering issue or a change in game state. More critically, in most "finished" products, panics are unacceptable: any unexpected failures should be handled elsewhere. That's where the new With the advent of good system error handling, we can now remove this. Note: I was instrumental in a) introducing this idea in the first place and b) pushing to make the panicking variant the default. The introduction of both `let else` statements in Rust and the fancy system error handling work in 0.16 have changed my mind on the right balance here. ## Solution 1. Make `Query::single` and `Query::single_mut` (and other random related methods) return a `Result`. 2. Handle all of Bevy's internal usage of these APIs. 3. Deprecate `Query::get_single` and friends, since we've moved their functionality to the nice names. 4. Add detailed advice on how to best handle these errors. Generally I like the diff here, although `get_single().unwrap()` in tests is a bit of a downgrade. ## Testing I've done a global search for `.single` to track down any missed deprecated usages. As to whether or not all the migrations were successful, that's what CI is for :) ## Future work ~~Rename `Query::get_single` and friends to `Query::single`!~~ ~~I've opted not to do this in this PR, and smear it across two releases in order to ease the migration. Successive deprecations are much easier to manage than the semantics and types shifting under your feet.~~ Cart has convinced me to change my mind on this; see https://github.com/bevyengine/bevy/pull/18082#discussion_r1974536085. ## Migration guide `Query::single`, `Query::single_mut` and their `QueryState` equivalents now return a `Result`. Generally, you'll want to: 1. Use Bevy 0.16's system error handling to return a `Result` using the `?` operator. 2. Use a `let else Ok(data)` block to early return if it's an expected failure. 3. Use `unwrap()` or `Ok` destructuring inside of tests. The old `Query::get_single` (etc) methods which did this have been deprecated.
80 lines
2.9 KiB
Rust
80 lines
2.9 KiB
Rust
//! Illustrates parallel queries with `ParallelIterator`.
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use bevy::{ecs::batching::BatchingStrategy, prelude::*};
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use rand::{Rng, SeedableRng};
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use rand_chacha::ChaCha8Rng;
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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(Camera2d);
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let texture = asset_server.load("branding/icon.png");
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// We're seeding the PRNG here to make this example deterministic for testing purposes.
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// This isn't strictly required in practical use unless you need your app to be deterministic.
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let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
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for z in 0..128 {
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commands.spawn((
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Sprite::from_image(texture.clone()),
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Transform::from_scale(Vec3::splat(0.1))
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.with_translation(Vec2::splat(0.0).extend(z as f32)),
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Velocity(20.0 * Vec2::new(rng.r#gen::<f32>() - 0.5, rng.r#gen::<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
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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
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.par_iter_mut()
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.for_each(|(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(window: Query<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
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let Ok(window) = window.single() else {
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return;
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};
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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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// The default batch size can also be overridden.
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// In this case a 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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sprites
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.par_iter_mut()
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.batching_strategy(BatchingStrategy::fixed(32))
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.for_each(|(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_systems(Startup, spawn_system)
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.add_systems(Update, (move_system, bounce_system))
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.run();
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}
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