We can use the read-only property, together with the
accessible role, to determine whether to set editable
and read-only states for at-spi. This lets us avoid
directly poking at the widgets.
ATs look at not just the implemented interfaces, but
also the states to decide what to do. It turns out that
the EditableText interface is only used by accerciser
if the editable state is set. So set it.
It is error prone to keep the same conditions in sync
in two places. Instead, just assemble the list of interfaces
as we register objects, and use when GetInterfaces is called.
Apply the Value implementation to the widgets where
we had one in GTK 3: GtkLevelBar, GtkRange, GtkScaleButton,
GtkSpinButton, GtkPaned, GtkProgressBar. To make these
work, the widgets need to set the accessible value properties.
There is some open question here whether the interface
should be implemented on the outer or the inner widget
of the entry-text pairs. For now, our hand is forced,
since only GtkText provides access to the layout that
we need for implementing many of the interface methods.
This is a not-quite-complete implementation of the
Text interface for GtkLabel. The missing parts are
anything around extents and positions, as well as
the ScrollSubstring apis.
This translates relations as far as the match.
I'm not sure yet what we can do about the fact that
atspi expects relations to be bidirectional (ie have
label-for *and* labelled-by) while aria has only one
direction.
It turns out that accerciser depends on this undocumented
method that is not in the xml at all, otherwise interface
sections in the accerciser ui never get enabled.
When we create the first AT-SPI context we also need to register the
accessible root on the accessibility bus. The accessible root object is
the main entry point of an accessible application, and it holds the
global state to present to the ATs that connect to the bus.
Since we need to check at run time what kind of AT context to use, we
need a hook into the whole GDK backend machinery. The display connection
seems to be the best choice, in this case, as it allows us to determine
whether we're running on an X11 or Wayland system, and thus whether we
should create a GtkAtSpiContext.
This requires some surgery to fix the GtkATContext creation function, in
order to include a GdkDisplay instance.
Does not do anything, at the moment, but it's going to get filled out
soon.
The backend is selected depending on the platform being compiled in;
since we're using AT-SPI on X11 and Wayland, and we don't have other
accessibility implementations, we currently don't care about run time
selection, but we're going to have to deal with that.
And generate the code for the DBus interfaces.
We don't want the full object manager experience, here, because we're
going to have a single object responding to various interfaces and
remote method calls. For this reason, we're not using the gnome module
in Meson to call gdbus-codegen for us: we need to use the interface info
command line arguments, and those are not available from Meson.
To build a better world sometimes means having to tear the old one down.
-- Alexander Pierce, "Captain America: The Winter Soldier"
ATK served us well for nearly 20 years, but the world has changed, and
GTK has changed with it. Now ATK is mostly a hindrance towards improving
the accessibility stack:
- it maps to a very specific implementation, AT-SPI, which is Linux and
Unix specific
- it requires implementing the same functionality in three different
layers of the stack: AT-SPI, ATK, and GTK
- only GTK uses it; every other Linux and Unix toolkit and application
talks to AT-SPI directly, including assistive technologies
Sadly, we cannot incrementally port GTK to a new accessibility stack;
since ATK insulates us entirely from the underlying implementation, we
cannot replace it piecemeal. Instead, we're going to remove everything
and then incrementally build on a clean slate:
- add an "accessible" interface, implemented by GTK objects directly,
which describe the accessible role and state changes for every UI
element
- add an "assistive technology context" to proxy a native accessibility
API, and assign it to every widget
- implement the AT context depending on the platform
For more information, see: https://gitlab.gnome.org/GNOME/gtk/-/issues/2833
