[Question] How to limit FPS?

[alexmozaidze]

I want to test wether delta time in my game works as expected and want to test the game on different fps, but there's no function to do that, can you add one, please? It's not even necessary for it to work on all platforms, just desktop would be nice, for debugging and stuff.

[buxx]

Hello @alexmozaidze , do https://docs.rs/macroquad/latest/macroquad/time/index.html is useful for you ?

[alexmozaidze]

Time module is useful for counting fps but not for limiting it.

[buxx]

My personal usage of this module is to make a sleep according to previous frame duration. By targeting my desired fps.

[alexmozaidze]

I don't know how to do that, I couldn't get any examples on the internet to work. Can you show an example of how to do that?

[buxx]

There is an example :

let minimum_frame_time = 1. / 60.; // 60 FPS
let frame_time = get_frame_time();
println!("Frame time: {}ms", frame_time * 1000.);
if frame_time < minimum_frame_time {
    let time_to_sleep = (minimum_frame_time - frame_time) * 1000.;
    println!("Sleep for {}ms", time_to_sleep);
    std::thread::sleep(std::time::Duration::from_millis(time_to_sleep as u64));
}

But this is not wasm compatible :( (std::thread cannot be used with wasm).

Anyone know how to make a sleep with wasm ?

[buxx]

I asked some information about sleep and wasm. There is the response I got :

---

You can't create a synchronous one, but to make an async one do this:

1. In your Javascript code declare this function:

export function js_sleep(ms) {
    let id;
    const promise = new Promise(resolve => id = setTimeout(resolve, ms));
    return [promise, id];
}
export function clear_timeout(x) {
    clearTimeout(x)
}

2. Write this Rust glue code:

#[wasm_bindgen(module = "/path/to/the/module.js")]
extern "C" {
    fn js_sleep(millis: u32) -> js_sys::Array;
    fn clear_timeout(id: i32);
}

pub async fn sleep(time: Duration) {
    let millis = u32::try_from(time.as_millis()).unwrap_or(u32::MAX);
    let tuple = js_sleep(millis);
    let promise = Promise::from(tuple.get(0));
    let id = tuple.get(1).as_f64().unwrap() as i32;
    struct Sleep {
        future: JsFuture,
        id: i32,
    }
    impl Future for Sleep {
        type Output = ();
        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
            Pin::new(&mut self.future).poll(cx).map(|res| { res.unwrap(); })
        }
    }
    impl Drop for Sleep {
        fn drop(&mut self) {
            clear_timeout(self.id);
        }
    }
    Sleep {
        future: JsFuture::from(promise),
        id,
    }
    .await
}

From then on you should be able to call sleep in Rust

[alexmozaidze]

With all that info, I now realize that having a function to limit fps is pretty limiting since it would take away the control from the developer. I'll change the title so it's easier to find by others. Thank you for helping me!

[DaLynX]

Hi, I am trying to achieve this but am still missing some bits like where to put this js code and how to regenerate a fully working gl.js file. Would you have some advice for that?

Also, don't you think this could be integrated in macroquad? Some developers like me 🙃 would be interested in having a sleep function.

[buxx]

I'm interested too. I tried by adding a sleep function (like in previous example) but I failed. @not-fl3 I have a question : Use a async_std::task::sleep could be a solution ?

[DaLynX]

It seems that's not supported in wasm yet: async-rs/async-std#220

[not-fl3]

Hi, I am trying to achieve this but am still missing some bits like where to put this js code and how to regenerate a fully working gl.js file. Would you have some advice for that?

Also, don't you think this could be integrated in macroquad? Some developers like me upside_down_face would be interested in having a sleep function.

There is no way to limit FPS on wasm, unfortunately: browser will send requestAnimationFrame frames as fast as it feels so, and there is not much we can do about it.

The only workaround: you can skip frames in your update logic, something like

if time_passed < desired frame_time {
  next_frame().await;
}

[DaLynX]

Right, I was trying to use thread::sleep so of course it didn't work but using macroquad::time::get_time() in an if block for my update code works fine. Thanks for pointing me to the right direction!

[des54321]

@not-fl3

Is there a reason macroquad doesn't seem to give a way to change the fps above 60?

[brettchalupa]

Curious about the question above ☝️

In theory, I don't see any reason why target_fps or max_fps couldn't be configured