Custom widgets in ATK

[Eric Williams <ericwill redhat com>]

Hello,

I am an Eclipse SWT developer, working to improve accessibility support 
for SWT on Linux.

Some background: SWT is a cross-platform Java UI toolkit which runs 
using GTK on Linux. Most SWT widgets match up to GTK widgets -- these 
are accessible by default via GTK. However we implement a custom GTK 
container, called SwtFixed, for custom widgets. These custom widgets do 
not map up to native GTK widgets and are drawn manually. The role of 
these widgets vary: from text editing to custom combos, etc. The main 
text editor in Eclipse is a custom widget, which means that 
accessibility for these widgets is important.

The issue: at present time, Orca is unable to read these custom widgets. 
It works on GTK2 semi-reliably, but GTK3 is unusable. Orca either hangs, 
crashes, or fails to read events/information from the custom widgets.

We currently have an accessibility implementation in SWT that was 
created long before GTK3 was around. From what I gather, it has not been 
regularly maintained since ~2012. The existing implementation uses ATK 
to enable accessibility in areas that GTK cannot (i.e., for custom 
widgets). I am virtually certain that the problem lies in the 
accessibility implementation, as the custom container implementation is 
accessible by default through GTK. I have confirmed this via testing.

Here is some of the code to register a custom widget with ATK:

(I've removed some of the Java typing to make it easier to read)

widgetType = G_OBJECT_TYPE (widget);
registry = atk_get_default_registry ();
factory = atk_registry_get_factory (registry, widgetType);
if (ATK_IS_NO_OP_OBJECT_FACTORY(factory)) return;

factoryName = FACTORY_TYPENAME + getTypeName(widgetType);

if (g_type_from_name (factoryName) == 0) {
        /* register the factory */
        GTypeInfo typeInfo = new GTypeInfo ();
        typeInfo.base_init = GTypeInfo_base_init_factory.getAddress ();
        typeInfo.class_size = (short)AtkObjectFactoryClass_sizeof ();
        typeInfo.instance_size = (short)AtkObjectFactory_sizeof ();
        
        info = g_malloc (GTypeInfo.sizeof);
        memmove (info, typeInfo, GTypeInfo.sizeof);
        swtFactoryType = g_type_register_static
                (ATK_TYPE_OBJECT_FACTORY(), factoryName, info, 0);
        parentType = atk_object_factory_get_accessible_type(factory);
        atk_registry_set_factory_type (registry, widgetType,
                swtFactoryType);
}


Another thing: I tried investigating with Accerciser, but it hangs and 
gives me the following error message:

WARNING **: 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.

I would appreciate it if someone could point me in the right direction. 
Is the code provided correct? Is there something additional we need to 
be doing to register with ATK?


Thanks,

--
Eric Williams
Associate Software Engineer - Eclipse Team
Red Hat