We cannot pass all the data we pass to the virtual function, because the
types are private, but the class and the signal are public API.
The signal is just a notification, so we can decouple the virtual
function (which stays the same, for internal types that implement the
ATContext API contract) from the signal.
If the ATContext state hasn't changed—for instance, if the accessible
attributes have been set to their default value, or have been set to the
same value—do not emit an accessible state change. State changes can be
arbitrarily expensive, so we want to ensure that they are meaningful.
Only GtkWidget should use GTK_ACCESSIBLE_ROLE_WIDGET as its default
accessible role; the default for GtkAccessible and GtkATContext should
be GTK_ACCESSIBLE_ROLE_NONE, meaning "an element whose implicit native
role semantics will not be mapped to the accessibility API", according
to the WAI-ARIA specification.
We want to test the accessibility API, as well as the implementation
inside each widget. For that, we should expose an API that lets us
verify that a GtkAccessible has a given role, as well as a given
property.
The API follows the pattern of other GTest API:
- a macro to assert that a condition is respected
- a function that prints out the error message in case of failure
While we have split the various attributes for convenience, there's no
reason why we should have specialised data types for the attributes
container object.
The ATContext type is meant to be used as the base class for
implementations of the assistive technology API—the actual mechanism
needed to communicate to components like the screen reader, or any other
AT.
Every time the widget state changes, the ATContext is meant to broadcast
the state change; and every time the AT queries the state of a UI
element, the ATContext is meant to provide that information.
We also have a "test" ATContext implementation, which is meant to be
used to write tests to verify that changes are propagated without
requiring a whole desktop session.
