[Kde-accessibility] Questions regarding AT-SPI and ATK
Gunnar Schmi Dt
gunnar at schmi-dt.de
Tue Jul 29 21:57:49 CEST 2003
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The KDE Accessibility Project is currently elaborating on what is the best way
to add AT-SPI support to Qt and KDE. Clearly this will be done by using the
Qt Accessibility Architecture (which currently gets extended by Trolltech).
However, there are a number of questions that IMO need to get solved:
1. What are the exact events that are used in AT-SPI and ATK?
2. Is there a possibility to determine whether there is an assistive
3. Is there a possibility for applications to do mouse (and keyboard) grabs
without stealing the AT applications mouse clicks?
4. As far as I have heard AT-SPI supports custom interfaces if an application
wants to provide information that is not handled within the AT-SPI standard.
How exactly does this work?
5. What are the exact dependencies of the required party of the AT-SPI
I will give some more details (and some background) for these questions:
1. In order to extend their accessibility framework, the Trolltech developers
need to know which events are used in AT-SPI and ATK and which details are
used to describe these events. As far as I looked there is no documentation
about the event types in AT-SPI. In ATK the documentation for the events is
spread over all interfaces. So far I found the following events:
Key press, Key release, Children change, Focus change, Property change,
State change, Visible data change, Selection changed, Column deleted,
Column inserted, Column reordered, Model changed, Row deleted,
Row inserted, Row reordered, Text attributes changed, Text caret moved,
Text changed, Text selection changed
Is this list complete? Which information describing those events is included
in these events?
2. In some cases preparing the events can be expensive. Therefore the Qt
Accessibility Architecture contains a method that returns true if there are
AT clients, and false if there are no AT clients. Clearly the easiest
implementation for this method when bridging to AT-SPI is to always return
true if the application got registered with the broker. On the other hand it
might be worth to do a more sophisticated implementation. For that we need to
be able to ask the broker whether there are AT clients. In that case we also
have to make sure that it is save to turn the sending of the events off when
there is no AT client.
3. One of the KDE developers wrote a prove-of-concept application that uses
the current Qt Accessibility Architecture. This application is called
Klaviatura and serves for two purposes: It can be used to remotely control
the menu bars, tool bars and popup menus of KDE applications, and it contains
an on-screen keyboard. Technically Klaviatura consists of a plug-in for Qt
and an external application. Both parts communicate with each other via DCOP.
When writing this application the developer found that applications often make
mouse grabs when showing pop up menus. If then a mouse click was intended to
go to an assistive technology it will be used by the wrong application.
In Klaviatura this problem is solved as follows:
The plug-in intercepts the event handling in order to be able to process mouse
clicks before the application processes them. If the mouse click was directed
to a window of Klaviatura that mouse click is intercepted and sent to the
Klaviatura application (via DCOP). Otherwise the mouse click is not
intercepted (and therefore will be processed by the application).
There are multiple possibilities for solving this issue in AT-SPI:
- - Avoid popup menus (and other things that require mouse grabs). This is not a
good solution as it interferes with the current user interface design of many
applications. Not showing a popup menu means either less functionality or (in
the case that you need an assistive technology to activate an entry in the
popup menu) less usability.
- - Do the popup menus without mouse grabs. This is not a good solution as pop
up menus need mouse grabs in order to work properly.
- -Send all mouse clicks to the ATs first and ask for a permission to process
- -Send those mouse clicks that are not directed to an application window to the
ATs and ask for a permission to process them.
The last two possibilities sound acceptable to me. I am not sure which is the
better one. Many assistive technologies might not be interested in processing
all mouse clicks, but there might be some few ATs that need top process them
Solving this problem will be important as some KDE developers will otherwise
have objections against AT-SPI.
4. Some KDE developers have concerns that AT-SPI is not powerfull enough. In
order to convince them that we will be able to extend the protocol if
necessary we need support for custom interfaces.
5. In order to get an acceptable solution for KDE we have to evaluate the
dependencies of those parts of the GNOME Accessibility Architecture that will
be used within KDE. When looking at ATK and the broker I fear that both will
most likely have too much dependencies. However, as we currently do not have
a clear position of KDE to AT-SPI, so I cannot say which dependencies will be
OK and which have to be changed.
If what I heard is correct the ATK dependencies are due a dependency on GAIL
which was introduced in order to force the user to have a working
architecture once ATK is installed. This dependency on GAIL pulls a
dependency on GNOME into ATK and should be avoided if we decide to use ATK in
The broker currently requires GTK+2. From a KDE perspective this dependency is
too much. When looking from outside on the broker one would think that
dependencies to glib and ORBIT2 would be enough.
Also the CORBA dependency might turn out to become a problem for many KDE
In either case I hope that we will find a clear position of KDE on the KDE
Developers Conference at the end of August.
Gunnar Schmi Dt
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