How to center a window when showing it | C++

[Evicia]

I'm trying to center a window when showing it,
I get the window size and then calculate the window position coordinates based on the screen size.

auto CenterPosition(slint::Window &window) const -> void
{
    const int screen_width = GetSystemMetrics(SM_CXSCREEN);
    const int screen_height = GetSystemMetrics(SM_CYSCREEN);
    auto size = window.size();  // 800*600
    slint::PhysicalPosition pos;
    pos.x = (screen_width - size.width) / 2;
    pos.y = (screen_height - size.height) / 2;
    window.set_position(pos);
}

But on Windows, calling size() on a window before it's displayed always returns 800*600, not its actual size. Calling size() on the window after it's displayed and centering it doesn't look pretty.

Is there any other way to center a window?

I will be grateful for help.

P.S I apologize for my auto-English.

[Abrahamiaan]

I am not sure but maybe you can just do something like

window.set_size({800, 600}) // if you want it to have constant size, just change to its actual size
CenterPosition(window);
window.show();

Or

window.show();
std::thread(&window {
std::this_thread::sleep_for(std::chrono::milliseconds(50)); // Just waiting the window to be opened
CenterPosition(window); // then only center it
}).detach();

Ping me if you need any help

[Evicia]

I see what you mean, thank you very much.

[Abrahamiaan]

If it works, please mark it as an answer. Thanks