desktop window: Add is-desktop AtkObject attribute

Screen readers need to distinguish between the desktop window and normal
windows, to be able to provide nicer speech synthesis.

This can be done by simply adding an "is-desktop" attribute to the
underlying AtkObject.

This is here done by introducing a thin caja_desktop_window_accessible_class
class which is based on GtkWindowAccessible and just appends the
attribute.

Closes: #999

src/caja-desktop-window.c

@@ -37,6 +37,41 @@
 #include <gio/gio.h>
 #include <glib/gi18n.h>    
 
+/* Tell screen readers that this is a desktop window */
+
+G_DEFINE_TYPE (CajaDesktopWindowAccessible, caja_desktop_window_accessible,
+               GTK_TYPE_WINDOW_ACCESSIBLE);
+
+static AtkAttributeSet *
+desktop_get_attributes (AtkObject *accessible)
+{
+    AtkAttributeSet *attributes;
+    AtkAttribute *is_desktop;
+
+    attributes = ATK_OBJECT_CLASS (caja_desktop_window_accessible_parent_class)->get_attributes (accessible);
+
+    is_desktop = g_malloc (sizeof (AtkAttribute));
+    is_desktop->name = g_strdup ("is-desktop");
+    is_desktop->value = g_strdup ("true");
+
+    attributes = g_slist_append (attributes, is_desktop);
+
+    return attributes;
+}
+
+static void
+caja_desktop_window_accessible_init (CajaDesktopWindowAccessible *window)
+{
+}
+
+static void
+caja_desktop_window_accessible_class_init (CajaDesktopWindowAccessibleClass *klass)
+{
+    AtkObjectClass *aclass = ATK_OBJECT_CLASS (klass);
+
+    aclass->get_attributes = desktop_get_attributes;
+}
+
 struct CajaDesktopWindowDetails
 {
     gulong size_changed_id;
@@ -289,6 +324,8 @@ caja_desktop_window_class_init (CajaDesktopWindowClass *klass)
     wclass->map = map;
     wclass->draw = draw;
 
+    gtk_widget_class_set_accessible_type (wclass, CAJA_TYPE_DESKTOP_WINDOW_ACCESSIBLE);
+
     nclass->window_type = CAJA_WINDOW_DESKTOP;
     nclass->get_title = real_get_title;
     nclass->get_icon = real_get_icon;

src/caja-desktop-window.h

@@ -32,6 +32,8 @@
 #include "caja-application.h"
 #include "caja-spatial-window.h"
 
+#include <gtk/gtk-a11y.h>
+
 #define CAJA_TYPE_DESKTOP_WINDOW caja_desktop_window_get_type()
 #define CAJA_DESKTOP_WINDOW(obj) \
   (G_TYPE_CHECK_INSTANCE_CAST ((obj), CAJA_TYPE_DESKTOP_WINDOW, CajaDesktopWindow))
@@ -64,4 +66,16 @@ CajaDesktopWindow *caja_desktop_window_new                 (CajaApplication *app
 void                   caja_desktop_window_update_directory    (CajaDesktopWindow *window);
 gboolean               caja_desktop_window_loaded              (CajaDesktopWindow *window);
 
+#define CAJA_TYPE_DESKTOP_WINDOW_ACCESSIBLE caja_desktop_window_accessible_get_type()
+
+typedef struct
+{
+  GtkWindowAccessible parent_spot;
+} CajaDesktopWindowAccessible;
+
+typedef struct
+{
+  GtkWindowAccessibleClass parent_spot;
+} CajaDesktopWindowAccessibleClass;
+
 #endif /* CAJA_DESKTOP_WINDOW_H */