Windows: High CPU Usage when not visible

[Kyryh]

Describe the bug
When not visible (by sending the egui::ViewportCommand::Visible(false) command) a simple egui application will use ~16% CPU on my CPU while using 0% otherwise

To Reproduce
Steps to reproduce the behavior:

1. Take the following egui application:

use eframe::egui;

fn main() -> Result<(), eframe::Error> {
    let options = eframe::NativeOptions {
        viewport: egui::ViewportBuilder::default().with_inner_size([320.0, 240.0]),
        ..Default::default()
    };

    eframe::run_simple_native("My egui App", options, move |ctx, _frame| {
        egui::CentralPanel::default().show(ctx, |ui| {
            ui.heading("My egui Application");
            if ui.button("Make invisible").clicked() {
                ctx.send_viewport_cmd(egui::ViewportCommand::Visible(false));
            }
        });
    })
}

2. Run it
3. Observe CPU usage while open, if the mouse cursor is not in the window or the window is minimized it will drop to 0
4. Press the button to make the window invisible
5. CPU usage will go up a lot

Expected behavior
CPU usage should stay low, similar to when it's minimized

Screenshots

Normally

When invisible

Desktop

• OS: Windows 11 26H1 (28000.1340)
• Version: eframe 0.33.3, also tested on latest master (bfaf1b4)

Additional context

• Issue persists even if the window is made invisible with WindowsAndMessaging::ShowWindow
• CPU usage resumes to be lower when the window is visible again
• Most of the issue's wording is taken directly from Windows: High CPU Usage when minimized #3982 since the issue is very similar (but not quite the same issue)
• Issue seems to be present with both the wgpu and glow backends

[Kamitai6]

I found a workaround for this issue on my environment.
The fix is to also check is_visible() in addition to is_minimized().

wgpu_integration.rs:

if let Some(window) = window
    && (window.is_minimized() == Some(true) || window.is_visible() == Some(false))
{
    // On Mac, a minimized Window uses up all CPU:
    // https://github.com/emilk/egui/issues/325
    profiling::scope!("minimized_sleep");
    std::thread::sleep(std::time::Duration::from_millis(10));
}

glow_integration.rs:

if window.is_minimized() == Some(true) || window.is_visible() == Some(false) {
    // On Mac, a minimized Window uses up all CPU:
    // https://github.com/emilk/egui/issues/325
    profiling::scope!("minimized_sleep");
    std::thread::sleep(std::time::Duration::from_millis(10));
}

I don't have time to submit a PR myself, but feel free to use this if anyone wants to pick it up.