Re: Which toplevel window is on top?

[Richard Shann <richard rshann plus com>]

On Sun, 2015-12-20 at 19:22 +0000, Emmanuele Bassi wrote:
> Hi;
>
> On 20 December 2015 at 18:01, Richard Shann <richard rshann plus com> wrote:
> > I would like to know which of the top-level windows in my application is
> > on top. Is there a way of doing this? I see that
>
> You can only see if your window has focus or contains the pointer —
> i.e. it's the one that the user is interacting with at this very
> moment. That usually implies that the window is at the top of the
> stack maintained by the window manager. You could also check if the
> "always-on-top" bit is set, but obviously that does not guarantee that
> the user is interacting with the window.
>
> Any other information about the window stack is maintained by the
> window manager itself, and you'll have to ask that component, using
> window manager and platform specific API, if an API is even exposed.
>
> > ------------------------------------------------------------------------
> > GdkEventVisibility has been deprecated since version 3.12 and should not
> > be used in newly-written code.
> >
> > Modern composited windowing systems with pervasive transparency make it
> > impossible to track the visibility of a window reliably, so this event
> > can not be guaranteed to provide useful information.
> > -------------------------------------------------------------------------
> > but is there an alternative for my (simpler) question?
>
> There is, sadly, nothing "simple" about your question. It truly
> depends on the platform, and on top of that, it depends on how your
> windows are managed.
>
> For instance, in a tiled window management policy, windows are not
> stacked — hence, there is no conventional "on top". Compositing window
> managers on X11, such as Mutter or Compiz, may re-arrange the windows
> as displayed to the user, even if the user cannot interact with them
> outside of the existing stacking order; again, "on top" is not
> something that can be conveyed to an API, when your windows are in
> "exposé" or laid out on the faces of a 3D solid. Finally, on Wayland,
> each surface has no knowledge of anything outside its own coordinate
> space; there is no way to access the windows stacking, and for all
> intent and purposes, your window manager may put the application's
> window on Mars.
>
> The only reliable way thing you can know is if the user is currently
> interacting with a window you're presenting, via pointer, touch, or
> keyboard events; either because the pointer or a finger entered the
> window, or because the window has key focus. GTK+ provides you with
> events to let you know when any of those things happens.

Thank you for your clear and comprehensive explanation. I think I will
need to provide an option to move all the windows inside a single
application window, or two if there are two screens.

Richard