Error when running application in WebGPU

[dsiea]

Hi Community,

I'm encountering an issue while trying to create a project for WebGPU. For WebGL, the example works perfectly, but when switching to WebGPU, I get the following error: panicked at library/std/src/sys/sync/condvar/no_threads.rs:19:9: condvar wait not supported
This error occurs during the request_adapter stage.

wasm-pack build --target web --debug

Has anyone else faced this problem or knows how to resolve it? Any help would be greatly appreciated.

I have attached the project archive

Thank you in advance!

github.zip
indexhtml.zip

[cwfitzgerald]

You can't use block_on on the web. The only reason it works on gl is that initialization of wgpu-core isn't actually asynchronous, so when running on non-webgpu the block_on doesn't actually need to wait.

[dsiea]

Thank you very much. I saw an example using block_on and decided that it was the right approach.

I added the following code, and the application started working with WebGPU. It might not be the best solution, but it’s a start.

#[cfg(target_arch = "wasm32")]
thread_local! {
    static RENDERER: std::cell::RefCell<Option<Renderer>> = std::cell::RefCell::new(None);
}

impl ApplicationHandler for App {
    fn resumed(&mut self, event_loop: &ActiveEventLoop) {
        let window_attributes = WindowAttributes::default()
            .with_title("WebGPU Test")
            .with_inner_size(PhysicalSize::new(800, 600));
        let window = event_loop.create_window(window_attributes).unwrap();

        #[cfg(target_arch = "wasm32")]
        {
            use winit::platform::web::WindowExtWebSys;
            // Setup canvas
            web_sys::window()
                .and_then(|win| win.document())
                .and_then(|doc| {
                    let dst = doc.get_element_by_id("wasm-example")?;
                    let canvas = web_sys::Element::from(window.canvas()?);
                    dst.append_child(&canvas).ok()?;
                    Some(())
                })
                .expect("Couldn't append canvas to document body.");

            let window = window;
            wasm_bindgen_futures::spawn_local(async move {
                match Renderer::new(window).await {
                    renderer => {
                        RENDERER.with(|cell| {
                            *cell.borrow_mut() = Some(renderer);
                        });
                    }
                }
            });
        }

        #[cfg(not(target_arch = "wasm32"))]
        {
            self.state = Some(pollster::block_on(Renderer::new(window)));
        }
    }
    
        fn window_event(
        &mut self,
        event_loop: &ActiveEventLoop,
        _window_id: winit::window::WindowId,
        event: WindowEvent,
    ) {
        #[cfg(target_arch = "wasm32")]
        if self.state.is_none() {
            // Try to get renderer from global state
            RENDERER.with(|cell| {
                if let Some(renderer) = cell.borrow_mut().take() {
                    self.state = Some(renderer);
                }
            });
        }
        // .... code
        }