Best way to determine user's screensize?

[2QdxY4RzWzUUiLuE at potatochowder.com]

On 2020-10-30 at 20:47:50 -0400,
songbird <songbird at anthive.com> wrote:

> Chris Angelico wrote:
> ...
> > I add my voice to those who detest applications that think they know
> > best and decide that they own the entire screen. It is incredibly
> > annoying.
> 
>   do you object to a window being put in the approximate
> center of the screen?

At times, yes.  At my last place of employment, I had a lot of screen
real estate.  It's very annoying to be working in a corner of it and
have some kind of modal dialog pop up way over there in the middle of
the screen.  In a dual screen setup when the screens are the same, "the
center of the screen" spans two physical screens.  If the screens are
different, then a window "in the center of the screen" might not even be
fully visible (e.g., two 1920x1080 screens, one portrait and one
landscape, positioned to form an "L").