59 lines
1.9 KiB
Rust
59 lines
1.9 KiB
Rust
//! This example illustrates how to react to component change.
|
|
|
|
use bevy::{ecs::world::Ref, prelude::*};
|
|
use rand::Rng;
|
|
|
|
fn main() {
|
|
App::new()
|
|
.add_plugins(DefaultPlugins)
|
|
.add_systems(Startup, setup)
|
|
.add_systems(
|
|
Update,
|
|
(change_component, change_detection, tracker_monitoring),
|
|
)
|
|
.run();
|
|
}
|
|
|
|
#[derive(Component, PartialEq, Debug)]
|
|
struct MyComponent(f32);
|
|
|
|
fn setup(mut commands: Commands) {
|
|
commands.spawn(MyComponent(0.));
|
|
commands.spawn(Transform::IDENTITY);
|
|
}
|
|
|
|
fn change_component(time: Res<Time>, mut query: Query<(Entity, &mut MyComponent)>) {
|
|
for (entity, mut component) in &mut query {
|
|
if rand::thread_rng().gen_bool(0.1) {
|
|
info!("changing component {:?}", entity);
|
|
let new_component = MyComponent(time.elapsed_seconds().round());
|
|
// Change detection occurs on mutable dereference,
|
|
// and does not consider whether or not a value is actually equal.
|
|
// To avoid triggering change detection when nothing has actually changed,
|
|
// you can use the `set_if_neq` method on any component or resource that implements PartialEq
|
|
component.set_if_neq(new_component);
|
|
}
|
|
}
|
|
}
|
|
|
|
// There are query filters for `Changed<T>` and `Added<T>`
|
|
// Only entities matching the filters will be in the query
|
|
fn change_detection(query: Query<(Entity, &MyComponent), Changed<MyComponent>>) {
|
|
for (entity, component) in &query {
|
|
info!("{:?} changed: {:?}", entity, component,);
|
|
}
|
|
}
|
|
|
|
// By using `Ref`, the query is not filtered but the information is available
|
|
fn tracker_monitoring(query: Query<(Entity, Ref<MyComponent>)>) {
|
|
for (entity, component) in &query {
|
|
info!(
|
|
"{:?}: {:?} -> {{is_added: {}, is_changed: {}}}",
|
|
entity,
|
|
component,
|
|
component.is_added(),
|
|
component.is_changed()
|
|
);
|
|
}
|
|
}
|