imcontext: Define a pango attribute for highlight

Define our own PangoAttribute type for IM Context
properties. Currently, the only defined property
is for marking the highlighted region.

gtk/gtkimcontext.c

@@ -1005,3 +1005,50 @@ gtk_im_context_set_property (GObject      *obj,
       break;
     }
 }
+
+
+static PangoAttribute *
+attr_preedit_properties_copy (const PangoAttribute *attr)
+{
+  const PangoAttrInt *int_attr = (PangoAttrInt *)attr;
+
+  return gtk_im_context_preedit_attr_new (int_attr->value);
+}
+
+static void
+attr_preedit_properties_destroy (PangoAttribute *attr)
+{
+  PangoAttrInt *iattr = (PangoAttrInt *)attr;
+
+  g_slice_free (PangoAttrInt, iattr);
+}
+
+static gboolean
+attr_preedit_properties_equal (const PangoAttribute *attr1,
+                               const PangoAttribute *attr2)
+{
+  const PangoAttrInt *int_attr1 = (const PangoAttrInt *)attr1;
+  const PangoAttrInt *int_attr2 = (const PangoAttrInt *)attr2;
+
+  return (int_attr1->value == int_attr2->value);
+}
+
+PangoAttribute *
+gtk_im_context_preedit_attr_new (GtkIMContextPreeditProperties value)
+{
+  PangoAttrInt *result = g_slice_new (PangoAttrInt);
+    static PangoAttrClass klass = {
+    0,
+    attr_preedit_properties_copy,
+    attr_preedit_properties_destroy,
+    attr_preedit_properties_equal
+  };
+
+  if (!klass.type)
+    klass.type = pango_attr_type_register ("GtkIMContextPreeditProperties");
+
+  pango_attribute_init (&result->attr, &klass);
+  result->value = value;
+
+  return (PangoAttribute *)result;
+}

gtk/gtkimcontext.h

@@ -168,6 +168,16 @@ gboolean gtk_im_context_delete_surrounding  (GtkIMContext       *context,
 					     int                 offset,
 					     int                 n_chars);
 
+
+typedef enum
+{
+  GTK_IM_CONTEXT_PREEDIT_CURSOR,
+} GtkIMContextPreeditProperties;
+
+GDK_AVAILABLE_IN_4_8
+PangoAttribute *        gtk_im_context_preedit_attr_new (GtkIMContextPreeditProperties value);
+
+
 G_END_DECLS
 
 #endif /* __GTK_IM_CONTEXT_H__ */