bevy/examples/systems.rs

use bevy::prelude::*;

/// Illustrates the different ways you can declare systems
fn main() {
    App::build()
        .add_default_plugins()
        .add_event::<MyEvent>()
        .add_startup_system(setup)
        .add_system_init(system_b)
        .add_system(System::for_each("system_a", system_a))
        .run();
}

struct MyEvent(usize);

// resources
struct A(usize);

// components
struct X(usize);
struct Y(usize);

// add our resources and entities
fn setup(world: &mut World, resources: &mut Resources) {
    resources.insert(A(0));
    world.insert((), vec![(X(0), Y(1)), (X(2), Y(3))]);
}

fn system_a((x, y): (Ref<X>, RefMut<Y>)) {

}

// fn system_a(x: Ref<X>, mut y: RefMut<Y>) {

// }
// fn system_a((my_events, a): &mut (Resource<Events<MyEvent>>, Resource<A>), (x, mut y): (Ref<X>, RefMut<Y>)) {

// }

fn system_b(resources: &mut Resources) -> Box<dyn Schedulable> {
    let mut my_event_reader = resources.get_event_reader::<MyEvent>();
    SystemBuilder::new("example")
        .read_resource::<Events<MyEvent>>()
        .write_resource::<A>()
        .with_query(<(Read<X>, Write<Y>)>::query())
        .build(move |_command_buffer, world, (my_events, ref mut a), query| {
            for event in my_event_reader.iter(&my_events) {
                a.0 += event.0;
                println!("modified resource A with event: {}", event.0);
            }
            for (x, mut y) in query.iter_mut(world) {
                y.0 += 1;
                println!("processed entity: {} {}", x.0, y.0);
            }
        })
}