Wayland compositors and accessibility

Simon Ser contact at emersion.fr
Mon Apr 15 19:23:51 UTC 2019

On Wednesday, April 3, 2019 4:00 PM, Samuel Thibault <samuel.thibault at ens-lyon.org> wrote:
> Olivier Fourdan, le mer. 03 avril 2019 14:39:29 +0200, a ecrit:
> > > What we currently have in Wayland is support for AccessX, directly
> > > implemented in mutter. The rest of accessibility features are currently
> > > mostly broken.
> >
> > Well, instead of "mostly broken", I'd say it's a WIP on the GNOME
> > side. To recap the state of the accessibility features in GNOME:
> Some of these cover what I mentioned indeed, but that does not cover the
> Orca needs for instance, and is GNOME-only. I'd really not push for a
> GNOME-only solution that would only leave disabled people with one
> choice of desktop, and not be able to use other people's computer which
> may not be running GNOME.

Do you have a list of accessibility features you'd like to have and a
description of what they do, how they look like?

> > -   For at-spi on Wayland, there is no global coordinates and no plan
> >     to add them. So for being able to generate pointer events without
> >     global coordinates and keyboard events without XTest for a replacement
> >     of dogtail which would work with GNOME on Wayland, there is ponytail:
> >
> >
> > https://gitlab.gnome.org/ofourdan/gnome-ponytail-daemon
> I am aware of this, but I thought this was mostly considered as a hack
> only for testing and not for production use?
> Apparently RecordWindow and Introspect are mutter/gnome-shell-specific,
> are they supposed to be implemented by other compositors as well?
> > > We could think
> > > of moving the implementation to a shared library that compositors
> > > would use, with the same principle as libinput. Such library could
> > > implement all accessibility features that a compositor should implement
> > > itself.
> >
> > Yet, I think this is quite different from what libinput does.
> Sure, the kind of processing is different. I just mean that such a
> library could be shared by compositors just like libinput is shared by
> compositors.
> > These features are very deeply rooted in the event loop of the
> > compositor, in the case of mutter, this is clutter.
> > Reason for this is because it need to be able to delay, replace or
> > inject both pointer (mousekeys) and keyboard events (slowkeys,
> > stickykeys, bouncekeys).
> Sure, that's what I mentioned above.
> > It also interfere with xkb state for modifiers (stickykeys). I reckon
> > moving the logic out of the compositor is certainly doable, but would
> > not necessarily make the code much simpler for other compositors...
> It seems to me that the current AccessX code is already quite involved
> compared to the interface it would require. And there is more that we
> would like to add for other accessibility features.
> > > It could also provide interfaces for plugging accessibility
> > > features implemented in separate processus (e.g. screen reader). To
> > > avoid keyloggers and such, such interface needs to be available only to
> > > trusted accessibility processes.
> >
> > That does not need to be Wayland protocols though, these could be DBUS.
> Sure.

A few things to keep in mind:

- If your feature needs to be strongly tied to Wayland (e.g. it needs
  to display a surface), Wayland protocols would probably be better
- Some compositors don't have D-Bus interfaces (e.g. KDE, Sway).

> > But I guess we need to define what a "trusted accessibility processes"
> > is and how the compositor can enforce that.
> Yes. AIUI there were already some discussions about this on
> wayland-devel?

There were some discussions about security, yes. As of now the
consensus mostly is: if the compositor starts the client, then it can
provide access to privileged interfaces.

> > > About the screen reader shortcuts, one issue we have with the current
> > > implementation is that for each keyboard event the toolkit has to wait
> > > for the screen reader to tell whether it ate the event or not. That
> > > makes all keyboard events get delayed. This should probably be replaced
> > > by a registration mechanism: the screen reader tells which shortcuts it
> > > is interested in, and only the events for them are captured and provided
> > > to the screen reader, asynchronously.
> > > Opinions on the whole thing?
> >
> > If the screenreader issue is just about keyboard shortcuts, then a
> > DBUS interface would be doable.
> There are also other use cases mentioned on the wiki page: e.g. virtual
> keyboard needing to inject keypresses, screen reader needing key events
> notification and mouse notification.
> But really, my main concern is that a mutter/gnome-shell-only solution
> is really not a proper solution, we need to define something that other
> compositors can easily implement too.


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