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
62 lines
2.2 KiB
Rust
62 lines
2.2 KiB
Rust
//! This example shows how you can know when a `Component` has been removed, so you can react to it.
|
|
|
|
use bevy::prelude::*;
|
|
|
|
fn main() {
|
|
// Information regarding removed `Component`s is discarded at the end of each frame, so you need
|
|
// to react to the removal before the frame is over.
|
|
//
|
|
// Also, `Components` are removed via a `Command`, which are not applied immediately.
|
|
// So you need to react to the removal at some stage after `apply_system_buffers` has run,
|
|
// and the Component` is removed.
|
|
//
|
|
// With these constraints in mind we make sure to place the system that removes a `Component` in
|
|
// `CoreSet::Update', and the system that reacts on the removal in `CoreSet::PostUpdate`.
|
|
App::new()
|
|
.add_plugins(DefaultPlugins)
|
|
.add_startup_system(setup)
|
|
.add_system(remove_component)
|
|
.add_system(react_on_removal.in_base_set(CoreSet::PostUpdate))
|
|
.run();
|
|
}
|
|
|
|
// This `Struct` is just used for convenience in this example. This is the `Component` we'll be
|
|
// giving to the `Entity` so we have a `Component` to remove in `remove_component()`.
|
|
#[derive(Component)]
|
|
struct MyComponent;
|
|
|
|
fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
|
|
commands.spawn(Camera2dBundle::default());
|
|
commands.spawn((
|
|
SpriteBundle {
|
|
texture: asset_server.load("branding/icon.png"),
|
|
..default()
|
|
},
|
|
// Add the `Component`.
|
|
MyComponent,
|
|
));
|
|
}
|
|
|
|
fn remove_component(
|
|
time: Res<Time>,
|
|
mut commands: Commands,
|
|
query: Query<Entity, With<MyComponent>>,
|
|
) {
|
|
// After two seconds have passed the `Component` is removed.
|
|
if time.elapsed_seconds() > 2.0 {
|
|
if let Some(entity) = query.iter().next() {
|
|
commands.entity(entity).remove::<MyComponent>();
|
|
}
|
|
}
|
|
}
|
|
|
|
fn react_on_removal(mut removed: RemovedComponents<MyComponent>, mut query: Query<&mut Sprite>) {
|
|
// `RemovedComponents<T>::iter()` returns an iterator with the `Entity`s that had their
|
|
// `Component` `T` (in this case `MyComponent`) removed at some point earlier during the frame.
|
|
for entity in &mut removed {
|
|
if let Ok(mut sprite) = query.get_mut(entity) {
|
|
sprite.color.set_r(0.0);
|
|
}
|
|
}
|
|
}
|