Re: Custom widgets in ATK

[Eric Williams <ericwill redhat com>]

This was very helpful, thank you for pointing me in the right direction.

Eric

On 08/22/2017 04:25 AM, Alejandro Piñeiro wrote:
> On 14/08/17 23:11, Eric Williams wrote:
> > Hello,
>
> Hi,
>
> a quick answer for your email below. Sorry for not answering before, I
> have just came back from holidays.
>
> > 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);
> > }
>
> ATK Factories are not the way to go anymore to extend already existing
> accessible objects/containers, now that most moder ATK implementations
> are not modules anymore. In fact, now I then I'm tempted to mark them as
> deprecated on ATK itself. The only reason I didn't do that is that there
> are still plenty of implementations using them, without no plans to port
> that code (AFAIK).
>
> > 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?
>
> On GTK3, the accessible implementation is public. We needed to ask that
> when they stopped to use factories, so apps/toolkits providing custom
> widgets could extend them. The poster boy at that moment was Evince. You
> mention that you have a custom container, so I hope that you are just
> extending GtkContainer. If that is the case this code could be used as
> an example:
>
> https://git.gnome.org/browse/evince/tree/libview/ev-view-accessible.c#n71
>
> I hope this helps.
>
> BR