mirror of
https://github.com/bevyengine/bevy
synced 2025-02-16 14:08:32 +00:00
bbb9849506
it's a followup of #1550 I think calling explicit methods/values instead of default makes the code easier to read: "what is `Quat::default()`" vs "Oh, it's `Quat::IDENTITY`" `Transform::identity()` and `GlobalTransform::identity()` can also be consts and I replaced the calls to their `default()` impl with `identity()`
45 lines
1.4 KiB
Rust
45 lines
1.4 KiB
Rust
use bevy::prelude::*;
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use rand::Rng;
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// This example illustrates how to react to component change
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fn main() {
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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(change_component.system())
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.add_system(change_detection.system())
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.add_system(flags_monitoring.system())
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.run();
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}
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#[derive(Debug)]
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struct MyComponent(f64);
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fn setup(mut commands: Commands) {
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commands.spawn((MyComponent(0.),));
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commands.spawn((Transform::identity(),));
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}
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fn change_component(time: Res<Time>, mut query: Query<(Entity, &mut MyComponent)>) {
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for (entity, mut component) in query.iter_mut() {
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if rand::thread_rng().gen_bool(0.1) {
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info!("changing component {:?}", entity);
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component.0 = time.seconds_since_startup();
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}
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}
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}
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// There are query filters for `Changed<T>`, `Added<T>` and `Mutated<T>`
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// Only entities matching the filters will be in the query
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fn change_detection(query: Query<(Entity, &MyComponent), Changed<MyComponent>>) {
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for (entity, component) in query.iter() {
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info!("{:?} changed: {:?}", entity, component,);
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}
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}
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// By looking at flags, the query is not filtered but the information is available
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fn flags_monitoring(query: Query<(Entity, Option<&MyComponent>, Option<Flags<MyComponent>>)>) {
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for (entity, component, flags) in query.iter() {
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info!("{:?}: {:?} -> {:?}", entity, component, flags,);
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}
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}
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