[wgpu] Add depth stencil initialization to Painter

[lsh]

I was getting panics in the egui_demo_app when using a depth buffer. To add the depth buffer I had modified:

// egui_demo_app/src/main.rs
let options = eframe::NativeOptions {
    drag_and_drop_support: true,

    initial_window_size: Some([1280.0, 1024.0].into()),

    #[cfg(feature = "wgpu")]
    renderer: eframe::Renderer::Wgpu,
    depth_buffer: 1, // <-- enable depth buffer

    ..Default::default()
};

and

// egui_demo_app/src/apps/custom3d_wgpu.rs
// in create_render_pipeline
depth_stencil: Some(wgpu::DepthStencilState {
    format: wgpu::TextureFormat::Depth32Float,
    depth_write_enabled: true,
    depth_compare: wgpu::CompareFunction::Less,
    stencil: wgpu::StencilState::default(),
    bias: wgpu::DepthBiasState::default(),
}),

I realized that because the first frame can render before the window is set, it is possible for depth_buffer to exist, while depth_texture_view to be None. This check stopped the crash for me, but if there is an issue with this solution I would be happy to refactor.

[Wumpf]

putting this into paint_and_update_textures doesn't really make sense as we don't check for a configured surface every frame either. Also don't quite understand why you're doing map().iter().for_each on a single element - you can just map to the correct thing right away :).

Anyways, it would be best if set_window would do the same on Some(window) as on_window_resized does on self.surface_state.is_some().

I.e. best to put

            self.configure_surface(width_in_pixels, height_in_pixels);
            let device = &self.render_state.as_ref().unwrap().device;
            self.depth_texture_view = self.depth_format.map(|depth_format| {
                device
                    .create_texture(&wgpu::TextureDescriptor {
                        label: Some("egui_depth_texture"),
                        size: wgpu::Extent3d {
                            width: width_in_pixels,
                            height: height_in_pixels,
                            depth_or_array_layers: 1,
                        },
                        mip_level_count: 1,
                        sample_count: 1,
                        dimension: wgpu::TextureDimension::D2,
                        format: depth_format,
                        usage: wgpu::TextureUsages::RENDER_ATTACHMENT
                            | wgpu::TextureUsages::TEXTURE_BINDING,
                    })
                    .create_view(&wgpu::TextureViewDescriptor::default())
            });

into a function and call it at both locations. If that's unclear I can help out!

[lsh]

@Wumpf thanks for explaining! Also feel free to suggest a better name for the texture view generator than resize_and_generate_depth_texture_view.

[Wumpf]

looks great and thanks for contributing!

I added a change-log entry myself since I forgot to mention that earlier (: