Comment # 2 on bug 1042529 from Stefan Hundhammer

We could use the window title as a handle to identify different main windows.

Based on that, we would need to use QSettings (which is quite trivial) to store
and retrieve window position and size for each of those main windows.

http://doc.qt.io/qt-5/qsettings.html

QSettings uses .ini file format, but in addition to the usual settings groups,
you can use paths for each key. We could normalize the window title (replace
all nonstandard characters that won't work for a key with "_", for example) and
use that as a path component for settings keys, e.g.

    /main_win/my_window_title/pos
    /main_win/my_window_title/size

There are very likely limitations that we would have to accept, such as all
those values getting invalid when the system language changes because the UI
only gets the translated window title (which would change in that case).

Restoring both position and size when opening a window is quite trivial.
Storing them would have to be done in that window's destructor which might
depend on the lifetime of that window being as long as that module runs (which
is always the case IMHO). When there are multiple main windows in the same
module, however, it might get somewhat inconsistent.

All in all I'd guess this is one day initial work and then one or two
additional days for fiddling with fringe cases we'd discover while testing it
for different modules and different desktop environments / window managers.

One caveat is that since YaST is always running as root, the settings would be
stored in root's home directory, i.e. they would be shared amont all users on
that machine that use YaST. For normal PCs, this is a non-issue, but for real
multi-user environments this might become somewhat annoying.