Moss

hey there! for our first little post here, i wanted to talk about how the idle game loop works and how we’re bridging bevy with tauri to create Mosswood Idle.

why this stack

mostly for speed of development and keeping concerns separate:

• bevy gives me a clean ECS world for a fully headless simulation.
• tauri makes it easy to ship cross-platform desktop/mobile apps.
• react is quick for building menu-driven UIs.

if we’re being real, though, it’s also just comfort. i love working in bevy, and while i don’t love react, i’ve used it for a decade so i’m pretty quick with it.

and with that…

the world ticks when the client asks it to

the bevy world doesn’t run continuously. instead, every 250ms, the client calls a tauri command that:

1. advances the simulation by the given delta.

2. returns a snapshot of the updated world state as JSON.

a simplified example

#[tauri::command]
fn update(delta: f32, state: State<AppState>) -> Snapshot {
    let mut backend = state.backend.lock();
    
    backend.update(Duration::from_millis(delta));
    backend.snapshot()
}

impl Backend {
		fn update(&mut self, delta: Duration) -> {
				self.app.world_mut().resource_mut::<TimeUpdateStrategy>() =
            TimeUpdateStrategy::ManualDuration(delta);

        self.app.update();
		}
}

setInterval(() => {
  invoke("update", { delta: 0.25 }).then((snapshot) => {
    setWorldState(snapshot);
  });
}, 250);

the offline tick

as an idle game, we gotta have offline progression. we do this pretty simply:

• on startup, we calculate how long the game has been closed.
• we then run the bevy world with the total delta in 250ms chunks.
• every chunk runs the simulation in full.
• a summary is returned of all progress made during catch-up.

about interactivity

it’s all tauri commands!

the client invokes a command → the backend pushes an event into bevy → an action system processes it.

what’s next?

i plan on writing more of these little architecture logs. some ideas i have:

• how villagers + tasks work in ECS.
• the data-driven content system.
• how save versions and migrations work.

you can follow along with the development of Mosswood Idle by either subscribing here or giving a follow on bluesky.