mirror of
https://github.com/bevyengine/bevy
synced 2024-09-20 14:32:06 +00:00
65252bb87a
Examples inconsistently use either `TAU`, `PI`, `FRAC_PI_2` or `FRAC_PI_4`. Often in odd ways and without `use`ing the constants, making it difficult to parse. * Use `PI` to specify angles. * General code-quality improvements. * Fix borked `hierarchy` example. Co-authored-by: devil-ira <justthecooldude@gmail.com>
91 lines
3 KiB
Rust
91 lines
3 KiB
Rust
//! Generic types allow us to reuse logic across many related systems,
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//! allowing us to specialize our function's behavior based on which type (or types) are passed in.
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//!
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//! This is commonly useful for working on related components or resources,
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//! where we want to have unique types for querying purposes but want them all to work the same way.
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//! This is particularly powerful when combined with user-defined traits to add more functionality to these related types.
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//! Remember to insert a specialized copy of the system into the schedule for each type that you want to operate on!
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//!
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//! For more advice on working with generic types in Rust, check out <https://doc.rust-lang.org/book/ch10-01-syntax.html>
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//! or <https://doc.rust-lang.org/rust-by-example/generics.html>
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use bevy::prelude::*;
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#[derive(Debug, Clone, Eq, PartialEq, Hash)]
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enum AppState {
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MainMenu,
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InGame,
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}
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#[derive(Component)]
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struct TextToPrint(String);
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#[derive(Component, Deref, DerefMut)]
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struct PrinterTick(Timer);
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#[derive(Component)]
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struct MenuClose;
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#[derive(Component)]
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struct LevelUnload;
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_state(AppState::MainMenu)
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.add_startup_system(setup_system)
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.add_system(print_text_system)
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.add_system_set(
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SystemSet::on_update(AppState::MainMenu).with_system(transition_to_in_game_system),
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)
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// add the cleanup systems
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.add_system_set(
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// Pass in the types your system should operate on using the ::<T> (turbofish) syntax
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SystemSet::on_exit(AppState::MainMenu).with_system(cleanup_system::<MenuClose>),
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)
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.add_system_set(
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SystemSet::on_exit(AppState::InGame).with_system(cleanup_system::<LevelUnload>),
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)
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.run();
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}
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fn setup_system(mut commands: Commands) {
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commands
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.spawn()
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.insert(PrinterTick(Timer::from_seconds(1.0, true)))
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.insert(TextToPrint(
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"I will print until you press space.".to_string(),
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))
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.insert(MenuClose);
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commands
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.spawn()
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.insert(PrinterTick(Timer::from_seconds(1.0, true)))
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.insert(TextToPrint("I will always print".to_string()))
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.insert(LevelUnload);
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}
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fn print_text_system(time: Res<Time>, mut query: Query<(&mut PrinterTick, &TextToPrint)>) {
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for (mut timer, text) in &mut query {
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if timer.tick(time.delta()).just_finished() {
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info!("{}", text.0);
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}
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}
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}
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fn transition_to_in_game_system(
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mut state: ResMut<State<AppState>>,
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keyboard_input: Res<Input<KeyCode>>,
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) {
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if keyboard_input.pressed(KeyCode::Space) {
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state.set(AppState::InGame).unwrap();
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}
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}
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// Type arguments on functions come after the function name, but before ordinary arguments.
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// Here, the `Component` trait is a trait bound on T, our generic type
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fn cleanup_system<T: Component>(mut commands: Commands, query: Query<Entity, With<T>>) {
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for e in &query {
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commands.entity(e).despawn_recursive();
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}
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}
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