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https://github.com/bevyengine/bevy
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81b53d15d4
Resolves #1253 #1562 This makes the Commands apis consistent with World apis. This moves to a "type state" pattern (like World) where the "current entity" is stored in an `EntityCommands` builder. In general this tends to cuts down on indentation and line count. It comes at the cost of needing to type `commands` more and adding more semicolons to terminate expressions. I also added `spawn_bundle` to Commands because this is a common enough operation that I think its worth providing a shorthand.
75 lines
2.9 KiB
Rust
75 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::build()
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.add_plugins(DefaultPlugins)
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.add_startup_system(setup.system())
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.add_system_to_stage(CoreStage::Update, remove_component.system())
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.add_system_to_stage(CoreStage::PostUpdate, react_on_removal.system())
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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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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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