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NPAPI:NativeAccessibility: Difference between revisions
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Since accessibility objects are living objects, they cannot be simply serialized over an IPC between the plugin process and the browser process. Instead, we utilize the AT-SPI registry to coalesce accessibiles from the two processes. Two corresponding objects are involved in this process in ATK, namely <tt>AtkPlug</tt> and <tt>AtkSocket</tt>. Together, they are used to connect accessibility hierarchies from different processes in a manner that is transparent to ATs. | Since accessibility objects are living objects, they cannot be simply serialized over an IPC between the plugin process and the browser process. Instead, we utilize the AT-SPI registry to coalesce accessibiles from the two processes. Two corresponding objects are involved in this process in ATK, namely <tt>AtkPlug</tt> and <tt>AtkSocket</tt>. Together, they are used to connect accessibility hierarchies from different processes in a manner that is transparent to ATs. | ||
In this example, the browser would create an <tt>AtkSocket</tt> object, and place it in the plugin's spot on the accessibility hierarchy. The plugin's out of process host would then call <tt>NPN_GetValue</tt> with <tt>NPNVNativeAccessibleAtkPlugId</tt> as the <tt>variable</tt> parameter. | In this example, the browser would create an <tt>AtkSocket</tt> object, and place it in the plugin's spot on the accessibility hierarchy in the main process. The plugin's out of process host would then call <tt>NPN_GetValue</tt> with <tt>NPNVNativeAccessibleAtkPlugId</tt> as the <tt>variable</tt> parameter. | ||
Compatible plugins would return the value of <tt>atk_plug_get_id()</tt> (a <tt>char*</tt>), or <tt>NULL</tt> indicating that they do not provide remote accessibility support. | Compatible plugins would return the value of <tt>atk_plug_get_id()</tt> (a <tt>char*</tt>), or <tt>NULL</tt> indicating that they do not provide remote accessibility support. | ||
A valid return value | A valid return value would be remoted to the main browser process, and used to attach the plug to the socket via <tt>atk_socket_embed()</tt>. The connection that is established via AT-SPI and atk-bridge in the background should be not only transparent to ATs, but seamless for the browser. | ||
Vendors are expected to use <tt>g_object_ref</tt> and <tt>g_object_unref</tt> as normal to manage the lifecycle of plugs and sockets. | |||
A detailed description of the mechanics of this API in the Linux accessibility stack is available on the [http://mail.gnome.org/archives/gnome-accessibility-devel/2009-September/msg00012.html gnome-accessibility-devel] mailing list. | A detailed description of the mechanics of this API in the Linux accessibility stack is available on the [http://mail.gnome.org/archives/gnome-accessibility-devel/2009-September/msg00012.html gnome-accessibility-devel] mailing list. | ||
''NOTE'': The proposed addition to ATK is not yet available, and slated for completion in Q1 2010. | ''NOTE'': The proposed addition to ATK is not yet available, and slated for completion in Q1 2010. | ||