Struggling with render pass lifetime

[Hperigo]

Hello, I'm trying to do a simple framework for experiments in webgpu, nothing super fancy but I'm struggling with render pass lifetime and the best way to architecture.

I'm taking the Framework from the wgpu examples folder as a start, but I'm stuck trying to do something like this:

RedrawRequested(_) => {	
   
		create encoder, render pass,... 
		 ui = create_dear_imgui_context ... 	

		example.render(state, ui, render_pass); //user code goes inside here 

		imgui_render(remder_pass)
		state.queue.submit(Some(encoder.finish()));	
}

where state is a struct containing the adapter, device, queue etc...

and inside the render function:

    fn render(&mut self, state: &wgpu_helper::State, render_pass: &mut RenderPass) {
        render_pass.set_bind_group(0, &self.bind_group, &[]);
        render_pass.set_pipeline(&self.pipeline);
        render_pass.set_index_buffer(self.index_buffer.slice(..), wgpu::IndexFormat::Uint16);
        render_pass.set_vertex_buffer(0, self.buffer.slice(..));
        render_pass.draw_indexed(0..6, 0, 0..1);
    }

but I get an error:

138 |     fn render(&mut self, state: &wgpu_helper::State, render_pass: &mut RenderPass) {
    |               -                                      ----------- has type `&mut RenderPass<'2>`
    |               |
    |               let's call the lifetime of this reference `'1`
139 |         render_pass.set_bind_group(0, &self.bind_group, &[]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`

The main reason for that would be to have the default render pass created as well dear imgui, so I wound't have to do this for every example.

I've been trying a couple of different things now and most of the time I run into some similar issue and TBH is very frustrating :/
here's the actual code:

 event_loop.run(move |event, _, control_flow| match event {
        winit::event::Event::RedrawRequested(_) => {
            let frame = match state.window_surface.get_current_texture() {
                Ok(frame) => frame,
                Err(_) => {
                    state.window_surface.configure(&state.device, &config);
                    state
                        .window_surface
                        .get_current_texture()
                        .expect("Failed to acquire next surface texture!")
                }
            };
            let view = frame.texture.create_view(&wgpu::TextureViewDescriptor {
                format: Some(surface_view_format),
                ..wgpu::TextureViewDescriptor::default()
            });

            let mut encoder = state
                .device
                .create_command_encoder(&wgpu::CommandEncoderDescriptor { label: None });

            {
                let mut rpass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                    label: None,
                    color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                        view: &view,
                        resolve_target: None,
                        ops: wgpu::Operations {
                            load: wgpu::LoadOp::Clear(wgpu::Color {
                                r: 0.1,
                                g: 0.2,
                                b: 0.3,
                                a: 1.0,
                            }),
                            store: true,
                        },
                    })],
                    depth_stencil_attachment: None,
                });

                example.render(&state, &mut rpass);
            }

            state.queue.submit(Some(encoder.finish()));

            frame.present();
        }
        winit::event::Event::MainEventsCleared => {
            window.request_redraw();
        }
        _ => {}
    });

anyway, any help is appreciated.

[cwfitzgerald]

Your signature should look like this:

fn render<'rpass>(&'rpass self, state: &State, rpass: &mut RenderPass<'rpass>)

This tells rust that data from within self can flow into the renderpass.

[Hperigo]

Thanks for the quick answer @cwfitzgerald but unfortunetly I get this error now:

   |
138 |     fn render<'rpass>(
    |               ------ lifetime `'rpass` defined here
...
141 |         render_pass: &'rpass mut RenderPass,
    |         ----------- has type `&mut RenderPass<'1>`
142 |     ) {
143 |         render_pass.set_bind_group(0, &self.bind_group, &[]);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'rpass` must outlive `'1`

[cwfitzgerald]

You put the lifetime in the wrong place

- &'rpass mut RenderPass,
+ &mut RenderPass<'rpass>

[Hperigo]

ohh, 🤦‍♂️

that worked! thanks for the help!