[PATCH] Introduce keyboard grabbing protocol

[Jonas Ådahl]

On Tue, Aug 30, 2016 at 02:12:29PM +0200, Giulio Camuffo wrote:
> 2016-08-30 13:58 GMT+02:00 Olivier Fourdan <ofourdan at redhat.com>:
> > Hi Giulio,
> >
> >> i have a couple of comments below
> >
> > Thanks a lot for your quick reply!
> >
> >> 2016-08-30 11:54 GMT+02:00 Olivier Fourdan <ofourdan at redhat.com>:
> >> > [...]
> >>
> >> I can understand the Xwayland use, but not the VM one. If i'm using a
> >> VM i expect it to receive key events when focused, not otherwise. If
> >> the point of this is just to inhibit the compositor's shortcuts than i
> >> think the protocol should just do that, and not do an actual grab.
> >> Additionally, as a user i'm not sure i would want my shortcuts to stop
> >> working, ever...
> >
> > On X11, some VM viewer will grab the keyboard and pointer so that all input events are set to the window, with one special shortcut to release those grabs - Using the grab keyboard protocol drafted here would allow to do that in Wayland as well.
> 
> I know they do, but while i understand the use of mouse grabbing to
> avoid going outside the window, i don't understand the use of keyboard
> grabbing. If the window is focused it will receive key events, if it's
> not focused as a user i would be surprised to see it still receiving
> events. But that doesn't happen, because to focus another window you
> need first to break the grab (and i assume an implementation of your
> protocol would break the grab when a surface from another client is
> focused). So, I can't see what key events would the grab actually
> intercept, besides the compositor's shortcuts.

I think having a grab would mean one is focused. Though the point of
having a key grabbing protocol is simply to override the compositors
keybindings. A virtual machine will be very annoying to work with if
you can't have the VM or remote desktop client override those. For
example I want to Alt-Tab inside the VM or inside the remotely
controlled desktop; I wouldn't want to be forced to reconfigure all
remotely controlled desktops or virtual machines to use Ctrl-Tab.

For this we need a way to steal input normally meant for the compositor.
Maybe "keyboard grab" is the wrong thing to call such a protocol, since
it shouldn't grab anything when its not in focus, it should only
override compositor bindings while already having keyboard focus (would
the compositor and user allow it).

If we leave Xwayland out for a bit, are you saying this should be on a
per key combination override instead? If so, how would a remote desktop
client, or virtual machine viewer know what bindings to override? It
won't know a thing about that is on the other side. Or what is it that
you suggest?


Jonas

> 
> >
> > Besides, reducing the use of the keyboard grab to Xwayland only might be a tad restrictive.
> >
> >> [...]
> >>
> >> I don't think it makes sense to send errors for those, it seems like
> >> both cases are out of the client's direct control and as such the
> >> client cannot be sure to avoid them, so it should survive when they
> >> happen.
> >
> > Oh absolutely, good point!
> >
> > Cheers,
> > Olivier
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