[UBUNTU] Resizing windows with no decorations does not immediately update window contents

[hampuslidin]

Description
When running a modified version of the standalone/02_hello_window example, which disables window decorations and calls winit::window::Window::drag_resize_window on left click, the window content is not updated immediately when the window is resized. Instead, it updates once you stop resizing for a fraction of a second. The attached video shows the issue while running on Ubuntu 24.04.2 LTS using an NVIDIA GeForce RTX™ 4060 Ti graphics card.

Repro steps
Example code:

use std::sync::Arc;

use winit::{
    application::ApplicationHandler,
    event::{WindowEvent, MouseButton},
    event_loop::{ActiveEventLoop, ControlFlow, EventLoop},
    window::{Window, WindowId, ResizeDirection},
};

struct State {
    window: Arc<Window>,
    device: wgpu::Device,
    queue: wgpu::Queue,
    size: winit::dpi::PhysicalSize<u32>,
    surface: wgpu::Surface<'static>,
    surface_format: wgpu::TextureFormat,
}

impl State {
    async fn new(window: Arc<Window>) -> State {
        let instance = wgpu::Instance::new(&wgpu::InstanceDescriptor::default());
        let adapter = instance
            .request_adapter(&wgpu::RequestAdapterOptions::default())
            .await
            .unwrap();
        let (device, queue) = adapter
            .request_device(&wgpu::DeviceDescriptor::default())
            .await
            .unwrap();

        let size = window.inner_size();

        let surface = instance.create_surface(window.clone()).unwrap();
        let cap = surface.get_capabilities(&adapter);
        let surface_format = cap.formats[0];

        let state = State {
            window,
            device,
            queue,
            size,
            surface,
            surface_format,
        };

        // Configure surface for the first time
        state.configure_surface();

        state
    }

    fn get_window(&self) -> &Window {
        &self.window
    }

    fn configure_surface(&self) {
        let surface_config = wgpu::SurfaceConfiguration {
            usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
            format: self.surface_format,
            // Request compatibility with the sRGB-format texture view we‘re going to create later.
            view_formats: vec![self.surface_format.add_srgb_suffix()],
            alpha_mode: wgpu::CompositeAlphaMode::Auto,
            width: self.size.width,
            height: self.size.height,
            desired_maximum_frame_latency: 2,
            present_mode: wgpu::PresentMode::AutoVsync,
        };
        self.surface.configure(&self.device, &surface_config);
    }

    fn resize(&mut self, new_size: winit::dpi::PhysicalSize<u32>) {
        self.size = new_size;

        // reconfigure the surface
        self.configure_surface();
    }

    fn render(&mut self) {
        // Create texture view
        let surface_texture = self
            .surface
            .get_current_texture()
            .expect("failed to acquire next swapchain texture");
        let texture_view = surface_texture
            .texture
            .create_view(&wgpu::TextureViewDescriptor {
                // Without add_srgb_suffix() the image we will be working with
                // might not be "gamma correct".
                format: Some(self.surface_format.add_srgb_suffix()),
                ..Default::default()
            });

        // Renders a GREEN screen
        let mut encoder = self.device.create_command_encoder(&Default::default());
        // Create the renderpass which will clear the screen.
        let renderpass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
            label: None,
            color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                view: &texture_view,
                depth_slice: None,
                resolve_target: None,
                ops: wgpu::Operations {
                    load: wgpu::LoadOp::Clear(wgpu::Color::GREEN),
                    store: wgpu::StoreOp::Store,
                },
            })],
            depth_stencil_attachment: None,
            timestamp_writes: None,
            occlusion_query_set: None,
        });

        // If you wanted to call any drawing commands, they would go here.

        // End the renderpass.
        drop(renderpass);

        // Submit the command in the queue to execute
        self.queue.submit([encoder.finish()]);
        self.window.pre_present_notify();
        surface_texture.present();
    }
}

#[derive(Default)]
struct App {
    state: Option<State>,
}

impl ApplicationHandler for App {
    fn resumed(&mut self, event_loop: &ActiveEventLoop) {
        // Create window object
        let window = Arc::new(
            event_loop
                .create_window(Window::default_attributes().with_decorations(false))
                .unwrap(),
        );

        let state = pollster::block_on(State::new(window.clone()));
        self.state = Some(state);

        window.request_redraw();
    }

    fn window_event(&mut self, event_loop: &ActiveEventLoop, _id: WindowId, event: WindowEvent) {
        let state = self.state.as_mut().unwrap();
        match event {
            WindowEvent::CloseRequested => {
                println!("The close button was pressed; stopping");
                event_loop.exit();
            }
            WindowEvent::RedrawRequested => {
                state.render();
                // Emits a new redraw requested event.
                state.get_window().request_redraw();
            }
            WindowEvent::Resized(size) => {
                // Reconfigures the size of the surface. We do not re-render
                // here as this event is always followed up by redraw request.
                state.resize(size);
            }
            WindowEvent::MouseInput {
                button: MouseButton::Left,
                ..
            } => {
                state.get_window().drag_resize_window(ResizeDirection::East).unwrap();
            }
            _ => (),
        }
    }
}

fn main() {
    // wgpu uses `log` for all of our logging, so we initialize a logger with the `env_logger` crate.
    //
    // To change the log level, set the `RUST_LOG` environment variable. See the `env_logger`
    // documentation for more information.
    env_logger::init();

    let event_loop = EventLoop::new().unwrap();

    // When the current loop iteration finishes, immediately begin a new
    // iteration regardless of whether or not new events are available to
    // process. Preferred for applications that want to render as fast as
    // possible, like games.
    event_loop.set_control_flow(ControlFlow::Poll);

    // When the current loop iteration finishes, suspend the thread until
    // another event arrives. Helps keeping CPU utilization low if nothing
    // is happening, which is preferred if the application might be idling in
    // the background.
    // event_loop.set_control_flow(ControlFlow::Wait);

    let mut app = App::default();
    event_loop.run_app(&mut app).unwrap();
}

Expected vs observed behavior
The window content should render the same on window resize regardless of whether decorations are disabled or not.

Extra materials
https://github.com/user-attachments/assets/d07f408e-5fbe-4d77-983d-ec337ee35303

Platform
wgpu version: trunk (3f96ba29804acf7710098ed1c2b352f8b8d07dc7)
OS: Ubuntu 24.04.2 LTS
GPU: NVIDIA GeForce RTX™ 4060 Ti

[kokosha]

A pull request from winit that may be related (rust-windowing/winit#2515). There is also a small example inside on how to use winit on X11 without decorations, that maybe can fix the problem.