The `get_child_at_index()` API model comes from AT-SPI, and it's not an
efficient design, especially when coupled with large widgets.
Replace `get_child_at_index()` with `get_first_accessible_child()` and
`get_next_accessible_sibling()`.
That allows efficiently retrieving all the children, simplifies the
implementation of GtkAccessible in GtkWidget and closely resembeles the
GtkWidget API.
Getting the last child and previous sibling for iterating backwards is
not a part of the interface at the moment, but they can be added at a
later date.
Note that this change required tracking the next stack page in
GtkStackPage.
Those property features don't seem to be in use anywhere.
They are redundant since the docs cover the same information
and more. They also created unnecessary translation work.
Closes#4904
Simplify getting the accessible role when checking if an accessible
implementation should present itself; this avoids going through
GtkAccessible twice to get the same data.
Since GtkATContexts are now lazily realized, we need to go through the
GtkAccessible's implementation to access the :accessible-role property,
in case there are fallbacks.
The ARIA spec is clear on this: when an element has the
HIDDEN state, it should not be presented in the accessible
tree.
This change is incomplete, we also need to emit child-added/
removed signals when the state changes, but that needs to
wait for the child added infrastructure to land.
platform change is called from gtk_widget_set_focusable
which is likely to be called early on in init(). We don't
want to create an AT context that early if we can help
it, e.g. since it makes it impossible to override the
accessible-role with a construct property.
As a companion to go with the platform_change api,
add a gtk_accessible_get_platform_state() function
that can be used by backends to get the platform
state.
This is in preparation for making entries inherit
their focus states from the text widget within.
Similar to gtk_widget_should_layout(), add a
gtk_accessible_should_present() function that backends can
use to determine whether an accessible should be presented
or not.
Ways to make a widget not presented in a11y:
- hide the widget
- set its role to NONE
- make it have a NULL AT context
We will use this in future to hide the GtkText inside
an entry, since the Text implementation will be done
by the wrapper.
Add an enum for 'platform changes' to the at context
change notification mechanism. This will let us pass
along things that ARIA considers 'platform state' such
as focus or editability. The difference between the
platform state and other ARIA states is that we don't
keep the platform state separately in the at context
- backends are expected to just query the widgets.
This is just about avoiding notify listeners for
change notification.
In some cases we explicitly want to unset an accessible attribute; for
instance, an accessible property is gated on a widget property, and if
the widget property gets unset, the accessible property should be reset.
We're currently overloading NULL to mean both "this value is undefined,
and should be reset to its default" and "the value collection failed".
Let's do error reporting right, by using GError to mean "the collection
failed, for this specific reason"; then, we can use a NULL return value
to signal that the accessible attribute should be reset to its default
value.
This is only relevant for pointer-sized attribute values: strings,
references, and reference lists; numeric, boolean, tristate, and token
values either cannot be undefined, or have a specific "undefined" value.
Some widgets have different roles after they are constructed, so we need
to allow changing the role defined by the class. We should still avoid
setting a role after the GtkATContext has been created.
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.
It's pointless, we can use an explicit value of `-1` everywhere.
Additionally, it complicates all code that uses the state enumeration as
an array index, since now we need to guard against a negative offset.
