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https://github.com/bevyengine/bevy
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dcc03724a5
# Objective NOTE: This depends on #7267 and should not be merged until #7267 is merged. If you are reviewing this before that is merged, I highly recommend viewing the Base Sets commit instead of trying to find my changes amongst those from #7267. "Default sets" as described by the [Stageless RFC](https://github.com/bevyengine/rfcs/pull/45) have some [unfortunate consequences](https://github.com/bevyengine/bevy/discussions/7365). ## Solution This adds "base sets" as a variant of `SystemSet`: A set is a "base set" if `SystemSet::is_base` returns `true`. Typically this will be opted-in to using the `SystemSet` derive: ```rust #[derive(SystemSet, Clone, Hash, Debug, PartialEq, Eq)] #[system_set(base)] enum MyBaseSet { A, B, } ``` **Base sets are exclusive**: a system can belong to at most one "base set". Adding a system to more than one will result in an error. When possible we fail immediately during system-config-time with a nice file + line number. For the more nested graph-ey cases, this will fail at the final schedule build. **Base sets cannot belong to other sets**: this is where the word "base" comes from Systems and Sets can only be added to base sets using `in_base_set`. Calling `in_set` with a base set will fail. As will calling `in_base_set` with a normal set. ```rust app.add_system(foo.in_base_set(MyBaseSet::A)) // X must be a normal set ... base sets cannot be added to base sets .configure_set(X.in_base_set(MyBaseSet::A)) ``` Base sets can still be configured like normal sets: ```rust app.add_system(MyBaseSet::B.after(MyBaseSet::Ap)) ``` The primary use case for base sets is enabling a "default base set": ```rust schedule.set_default_base_set(CoreSet::Update) // this will belong to CoreSet::Update by default .add_system(foo) // this will override the default base set with PostUpdate .add_system(bar.in_base_set(CoreSet::PostUpdate)) ``` This allows us to build apis that work by default in the standard Bevy style. This is a rough analog to the "default stage" model, but it use the new "stageless sets" model instead, with all of the ordering flexibility (including exclusive systems) that it provides. --- ## Changelog - Added "base sets" and ported CoreSet to use them. ## Migration Guide TODO
61 lines
2.2 KiB
Rust
61 lines
2.2 KiB
Rust
//! This example shows how you can know when a `Component` has been removed, so you can react to it.
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use bevy::prelude::*;
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fn main() {
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// Information regarding removed `Component`s is discarded at the end of each frame, so you need
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// to react to the removal before the frame is over.
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//
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// Also, `Components` are removed via a `Command`, which are not applied immediately.
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// So you need to react to the removal at some stage after `apply_system_buffers` has run,
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// and the Component` is removed.
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//
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// With these constraints in mind we make sure to place the system that removes a `Component` in
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// `CoreSet::Update', and the system that reacts on the removal in `CoreSet::PostUpdate`.
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App::new()
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.add_plugins(DefaultPlugins)
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.add_startup_system(setup)
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.add_system(remove_component)
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.add_system(react_on_removal.in_base_set(CoreSet::PostUpdate))
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.run();
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}
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// This `Struct` is just used for convenience in this example. This is the `Component` we'll be
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// giving to the `Entity` so we have a `Component` to remove in `remove_component()`.
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#[derive(Component)]
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struct MyComponent;
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fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
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commands.spawn(Camera2dBundle::default());
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commands.spawn((
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SpriteBundle {
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texture: asset_server.load("branding/icon.png"),
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..default()
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},
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// Add the `Component`.
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MyComponent,
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));
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}
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fn remove_component(
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time: Res<Time>,
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mut commands: Commands,
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query: Query<Entity, With<MyComponent>>,
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) {
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// After two seconds have passed the `Component` is removed.
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if time.elapsed_seconds() > 2.0 {
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if let Some(entity) = query.iter().next() {
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commands.entity(entity).remove::<MyComponent>();
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}
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}
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}
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fn react_on_removal(mut removed: RemovedComponents<MyComponent>, mut query: Query<&mut Sprite>) {
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// `RemovedComponents<T>::iter()` returns an iterator with the `Entity`s that had their
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// `Component` `T` (in this case `MyComponent`) removed at some point earlier during the frame.
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for entity in &mut removed {
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if let Ok(mut sprite) = query.get_mut(entity) {
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sprite.color.set_r(0.0);
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}
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}
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}
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