Re: one desktop, two people, two keyboards and mice

[Peter Hutterer <peter hutterer who-t net>]

On Sun, Mar 22, 2020 at 07:08:51PM +0000, Richard Henwood via desktop-devel-list wrote:
> Hi All,
> I have a large monitor, and I would like to use my computer with my child.
> My vision is for me and my child to have our own keyboards and mice. I
> imagine working away on 'my side' of the screen, while they are working on
> their side. Occasionally, I will 'reach across' and help them with what
> they are working on.

As Niels already pointed out, multiseat is the word to look for here.
However, the most common documentation on multiseat you will find is for
separate sessions on the same host computer. The goal is to save on
hardware, not collaboration.

If you google for MPX or Multi-Pointer X, that provides what you need and
it's been supported in X since 2008 or so. Should be immediately available
via:

xinput create-master "somename"
xinput reattach "my usb mouse name" "somename pointer"
xinput reattach "my keyboard name" "somename keyboard"

You'll get the various device names from "xinput list", the master device
name is whatever you want it to be.

however... MPX is a very niche case and not used very often, which means
there will be bugs lurking. GTK3 supports it natively to some degree but
there are limitations because the whole interaction with the desktop
changes and becomes a lot more complicated - and for something that's that 
niche, surprisingly not everything got rewritten :)

The general rule is: while you're interacting in two different X clients,
things will probably work, but when you're interacting with the same one,
that client will get confused. Unfortunately that also applies to the window
manager - moving two windows at the same time won't work.

For Wayland compositors - I think setting the ID_SEAT property on the input
devices to 'seat1' (default is seat0) should be sufficient to get them into
a new wl_seat and thus all of the above. I haven't played with that in a
long time though but unlike X, Wayland supports this in the core protocol.
Even if it works, expect the same bugs and issues because of it's niche
functionality and the massive effort required to actually make this work.

Cheers,
   Peter
 
> I think libinput is part of the solution here. I added two mice it roughly
> worked but there are mice cursor artifacts. I guess that GNOME or possibly
> Wayland also needs some concept of multiple simultaneous inputs? I am on
> an Ubuntu 18.04 distro, so may be things have improved with more recent
> releases?
> So, in short, does anyone have any pointers or suggestions for me to
> follow-up with?
> best regards,Richard