a9a4b069b6
# Objective
- Improve reproducibility of examples
## Solution
- Use seeded rng when needed
- Use fixed z-ordering when needed
## Testing
```sh
steps=5;
echo "cpu_draw\nparallel_query\nanimated_fox\ntransparency_2d" > test
cargo run -p example-showcase -- run --stop-frame 250 --screenshot-frame 100 --fixed-frame-time 0.05 --example-list test --in-ci;
mv screenshots base;
for prefix in `seq 0 $steps`;
do
echo step $prefix;
cargo run -p example-showcase -- run --stop-frame 250 --screenshot-frame 100 --fixed-frame-time 0.05 --example-list test;
mv screenshots $prefix-screenshots;
done;
mv base screenshots
for prefix in `seq 0 $steps`;
do
echo check $prefix
for file in screenshots/*/*;
do
echo $file;
diff $file $prefix-$file;
done;
done;
```
77 lines
2.8 KiB
Rust
77 lines
2.8 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.gen::<f32>() - 0.5, rng.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: Single<&Window>, mut sprites: Query<(&Transform, &mut Velocity)>) {
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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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