Ability to make windows start centered

[PlanetTeamSpeakk]

It seems like it is not possible to make a window start in the center of the screen it launches on. I have found it's possible to set the position of the window before showing it, which, in combination with the size of the screen and of the window, can be used to make it start at the center, except it appears to be impossible to find out the size of the screen that the window will be shown on, hence it seems to be impossible to make it start centred.

Thus, I would like to request a feature to do this.

[ogoffart]

Thanks for the feature request.
This was discussed in #3859

[PlanetTeamSpeakk]

The linked discussion seems to have gotten about as far as I did. Afaik, it's not possible to get the monitor the window is on from winit to calculate the center with.

Also, the discussion mentions that there aren't many use cases for this, but I'd like to add that my personal use case is that my window is very small and having it open in the top left corner of my screen is very annoying. I have currently resorted to restoring the position from last session, but I'd still like for this feature to be added. A simple center_on_screen() function or something like that would be great.

[prof79]

I second that, MS XAML has WindowStartupLocation and other frameworks have their not-too-complicated ways (eg. https://wiki.qt.io/How_to_Center_a_Window_on_the_Screen, https://stackoverflow.com/questions/17908584/how-to-set-the-gtk-window-to-the-center-of-screen).

Especially small windows on big screens are a problem. With smaller windows I need to drag them in the middle because that's where my comfortable focus point for interaction is, regarding eye/head movement.

[prof79]

That was a tough act taking several hours, at least an idea of how this might be done. The dynamic AppWindow structure and winit API changes in-between didn't make things any easier.

https://github.com/prof79/slint-center-window

[ogoffart]

@prof79 Thanks for sharing the example.

Btw, since this might be a common use case, I was thinking maybe we could add an enum in the WindowPosition enum to have it centered. https://slint.dev/docs/rust/slint/enum.WindowPosition
Too bad it isn't non_exhaustive