Adventures in calling Atspi from JavaScript

[Joseph Scheuhammer <clown alum mit edu>]

All,

I've been implementing a JavaScript object for use within GNOME Shell 
that tracks the keyboard focus and the caret. I am using 
GObjectIntrospection to communicate between JavaScript and AT-SPI. Some 
things are working, but others aren't. Descriptions of the problems are 
given below. If you see anything that sheds light on things, let me know.

1. Registering 'object:text-caret-moved' always results in an error.

The actual error is garbled, containing non-printable characters. Here 
is what I get:

> Window manager warning: Log level 16: Atspi: Adding match: Interface name
> 'org.a11y.atspi.Event.object' is invalid.

How it's registered. Note that 'this._atspiEventListener' is an 
Atspi.EventListener, or, in C, an AtspiEventListener:

registered = this._atspiEventListener.register_from_callback(
_atspiCaretCB, 'object:text-caret-moved'
);

- the returned value, 'registered', is 'true'.
- the callback, '_atspiCaretCB', is never called.
- I do the same thing for 'object:state-changed:focused' and 
'object:state-changed:selected', and that works fine.

2. Focus tracking doesn't work with St widgets.

Registering for 'object:state-changed:focused' and 
'object:state-changed:selected' works great with GTK widgets, and even 
within web pages with ARIA widgets. But, whenever a GNOME Shell widget 
is invoked, the system freezes for about 5 - 10 seconds. When the UI is 
responsive again, the event passed back, has no accessible component 
within it.

Examples of GNOME Shell widgets are the task switcher, adn the 
accessibility menu on the top right.

- the callback is passed an AT-SPI event (which is correct).
- the event.type is 'object:state-changed:focused' (which is correct).
- the event.source is non-null, but has no accessible name.
- calling get_component() on the event.source returns null. Thus, there 
is no way to get an extents rectangle for the focussed item.
- sometimes the following error message is output:

> Window manager warning: Log level 16: AT-SPI: Error in GetItems,
> sender=(null), error=Did not receive a reply. Possible causes 
include: the
> remote application did not send a reply, the message bus security policy
> blocked the reply, the reply timeout expired, or the network 
connection was
> broken.

3. Deregistering callbacks doesn't actually deregister.

Or, I don't understand what "deregister" means :-).

When deregister_from_callback() is called, the return value is 'true', 
suggesting that the event has been deregistered. However, the callback 
that was supplied during the prior register_from_callback() is still 
invoked. It's as if the system is saying, "Okay, you've been 
disconnected as requested", but nonetheless keeps calling back when the 
event occurs.

The way it's deregistered:
deregistered = this._atspiEventListener.deregister_from_callback(
_atspiFocusCB, 'object:state-changed:focused'
);

- the returned value, deregistered, is 'true'
- the callback, _atspiFocusCB, continues to be called.

Thanks for any suggestions.

--
;;;;joseph.


'A: After all, it isn't rocket science.'
'K: Right. It's merely computer science.'
             - J. D. Klaun -