fn main() -> Result<()> {
    let event_loop = EventLoop::new();
    // (1) Call Integration::new() in App::new().
    let mut app = App::new(&event_loop)?;

    event_loop.run(move |event, _, control_flow| {
        *control_flow = ControlFlow::Poll;
        // (2) Call integration.handle_event(&event).
        app.egui_integration.handle_event(&event);
        match event {
            Event::WindowEvent {
                event: WindowEvent::CloseRequested,
                ..
            } => *control_flow = ControlFlow::Exit,
            Event::WindowEvent {
                event: WindowEvent::Resized(_),
                ..
            } => {
                // (3) Call integration.recreate_swapchain(...) in app.recreate_swapchain().
                app.recreate_swapchain().unwrap();
            }
            Event::MainEventsCleared => app.window.request_redraw(),
            Event::RedrawRequested(_window_id) => {
                // (4) Call integration.begin_frame(), integration.end_frame(&mut window),
                // integration.context().tessellate(shapes), integration.paint(...)
                // in app.draw().
                app.draw().unwrap();
            }
            _ => (),
        }
    })
}
// (5) Call integration.destroy() when drop app.