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https://github.com/bevyengine/bevy
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07ed1d053e
This implements the most minimal variant of #1843 - a derive for marker trait. This is a prerequisite to more complicated features like statically defined storage type or opt-out component reflection. In order to make component struct's purpose explicit and avoid misuse, it must be annotated with `#[derive(Component)]` (manual impl is discouraged for compatibility). Right now this is just a marker trait, but in the future it might be expanded. Making this change early allows us to make further changes later without breaking backward compatibility for derive macro users. This already prevents a lot of issues, like using bundles in `insert` calls. Primitive types are no longer valid components as well. This can be easily worked around by adding newtype wrappers and deriving `Component` for them. One funny example of prevented bad code (from our own tests) is when an newtype struct or enum variant is used. Previously, it was possible to write `insert(Newtype)` instead of `insert(Newtype(value))`. That code compiled, because function pointers (in this case newtype struct constructor) implement `Send + Sync + 'static`, so we allowed them to be used as components. This is no longer the case and such invalid code will trigger a compile error. Co-authored-by: = <=> Co-authored-by: TheRawMeatball <therawmeatball@gmail.com> Co-authored-by: Carter Anderson <mcanders1@gmail.com>
76 lines
2.9 KiB
Rust
76 lines
2.9 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`. `Command`s are applied after a stage has
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// finished executing. So you need to react to the removal at some stage after the
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// `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` on
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// the `CoreStage::Update' stage, and the system that reacts on the removal on the
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// `CoreStage::PostUpdate` stage.
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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_to_stage(CoreStage::Update, remove_component)
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.add_system_to_stage(CoreStage::PostUpdate, react_on_removal)
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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(
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mut commands: Commands,
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asset_server: Res<AssetServer>,
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mut materials: ResMut<Assets<ColorMaterial>>,
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) {
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let texture = asset_server.load("branding/icon.png");
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commands.spawn_bundle(OrthographicCameraBundle::new_2d());
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commands
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.spawn_bundle(SpriteBundle {
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material: materials.add(texture.into()),
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..Default::default()
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})
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.insert(MyComponent); // Add the `Component`.
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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.seconds_since_startup() > 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(
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mut materials: ResMut<Assets<ColorMaterial>>,
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removed: RemovedComponents<MyComponent>,
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query: Query<(Entity, &Handle<ColorMaterial>)>,
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) {
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// Note: usually this isn't how you would handle a `Query`. In this example it makes things
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// a bit easier to read.
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let (query_entity, material) = query.iter().next().unwrap();
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// `RemovedComponents<T>::iter()` returns an interator 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 removed.iter() {
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// We compare the `Entity` that had its `MyComponent` `Component` removed with the `Entity`
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// in the current `Query`. If they match all red is removed from the material.
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if query_entity == entity {
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materials.get_mut(material).unwrap().color.set_r(0.0);
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}
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}
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}
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