Bevy 0.11 - How to have two systems running in different fixed time steps ?

[didibear]

In the Bevy Examples here, it shows how to have systems running in the same fixed time step:

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(FixedUpdate, fixed_update)
        .insert_resource(FixedTime::new_from_secs(0.5)) 
        // ^ How to add system with another fixed time step ?
        .run();
}

But I cannot find the way to setup two systems running in different time steps.

In bevy 0.9, it was possible using the FixedTimestep system criteria in a SystemSet as shown in the Bevy Cheat Book here:

use bevy::time::FixedTimestep;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_system_set(
            SystemSet::new()
                // This prints out "hello world" once every second
                .with_run_criteria(FixedTimestep::step(1.0))
                .with_system(slow_timestep)
        )
        .add_system_set(
            SystemSet::new()
                // This prints out "goodbye world" twice every second
                .with_run_criteria(FixedTimestep::step(0.5))
                .with_system(fast_timestep)
        )
        .run();
}

fn slow_timestep() {
    println!("hello world");
}

fn fast_timestep() {
    println!("goodbye world");
}

What is the way to do that in bevy 0.11 ?

[alice-i-cecile]

Generally speaking, you really only want one fixed timestep: this should be used for synchronizing all of your logic for physics and networking stability.

If you just want to run your system every x seconds use a on_timer run condition instead.

If I'm wrong and you really, really want two copies of the looping logic, dig into the source code and cannabilize what we've done with the outer schedule: it should all be user reproducible.

[didibear]

Thanks ! on_timer is exactly what I was looking for to have game logic based on time.
For example on a snake game:

.add_systems(
    Update,
    (
        update_positions.run_if(on_timer(Duration::from_millis(100))),
        spawn_food.run_if(on_timer(Duration::from_secs(3))),
    )
)

[alice-i-cecile]

Yep, that's precisely the pattern I'd use it for :)