root: Add focus

Add a getter and a setter for the focus widget.
The default implementations do nothing.

gtk/gtkroot.c

@@ -21,6 +21,8 @@
 
 #include "gtkrootprivate.h"
 #include "gdk/gdk-private.h"
+#include "gtkprivate.h"
+#include "gtkintl.h"
 
 /**
  * SECTION:gtkroot
@@ -65,6 +67,13 @@ gtk_root_default_init (GtkRootInterface *iface)
   iface->get_display = gtk_root_default_get_display;
   iface->get_renderer = gtk_root_default_get_renderer;
   iface->get_surface_transform = gtk_root_default_get_surface_transform;
+
+  g_object_interface_install_property (iface,
+      g_param_spec_object ("focus-widget",
+                           P_("Focus widget"),
+                           P_("The focus widget"),
+                           GTK_TYPE_WIDGET,
+                           GTK_PARAM_READWRITE|G_PARAM_EXPLICIT_NOTIFY));
 }
 
 GdkDisplay *
@@ -124,3 +133,63 @@ gtk_root_get_for_surface (GdkSurface *surface)
 
   return NULL;
 }
+
+/**
+ * gtk_root_set_focus:
+ * @self: a #GtkRoot
+ * @focus: (allow-none): widget to be the new focus widget, or %NULL
+ *    to unset the focus widget
+ *
+ * If @focus is not the current focus widget, and is focusable, sets
+ * it as the focus widget for the root. If @focus is %NULL, unsets
+ * the focus widget for the root.
+ *
+ * To set the focus to a particular widget in the root, it is usually
+ * more convenient to use gtk_widget_grab_focus() instead of this function.
+ */
+void
+gtk_root_set_focus (GtkRoot   *self,
+                    GtkWidget *focus)
+{
+  g_return_if_fail (GTK_IS_ROOT (self));
+  g_return_if_fail (focus == NULL || GTK_IS_WIDGET (focus));
+
+  g_object_set (self, "focus-widget", focus, NULL);
+}
+
+/**
+ * gtk_root_get_focus:
+ * @self: a #GtkRoot
+ *
+ * Retrieves the current focused widget within the root.
+ *
+ * Note that this is the widget that would have the focus
+ * if the root is active; if the root is not focused then
+ * `gtk_widget_has_focus (widget)` will be %FALSE for the
+ * widget.
+ *
+ * Returns: (nullable) (transfer none): the currently focused widget,
+ *    or %NULL if there is none.
+ */
+GtkWidget *
+gtk_root_get_focus (GtkRoot *self)
+{
+  GtkWidget *focus;
+
+  g_return_val_if_fail (GTK_IS_ROOT (self), NULL);
+
+  g_object_get (self, "focus-widget", &focus, NULL);
+
+  if (focus)
+    g_object_unref (focus);
+
+  return focus;
+}
+
+guint
+gtk_root_install_properties (GObjectClass *object_class,
+                             guint         first_prop)
+{
+  g_object_class_override_property (object_class, first_prop + GTK_ROOT_PROP_FOCUS_WIDGET, "focus-widget");
+  return GTK_ROOT_NUM_PROPERTIES;
+}

gtk/gtkroot.h

@@ -56,6 +56,12 @@ struct _GtkRootInterface
 GDK_AVAILABLE_IN_ALL
 GtkWidget * gtk_root_get_for_surface (GdkSurface *surface);
 
+GDK_AVAILABLE_IN_ALL
+void        gtk_root_set_focus (GtkRoot   *self,
+                                GtkWidget *focus);
+GDK_AVAILABLE_IN_ALL
+GtkWidget * gtk_root_get_focus (GtkRoot   *self);
+
 G_END_DECLS
 
 #endif /* __GTK_ROOT_H__ */

gtk/gtkrootprivate.h

@@ -11,6 +11,14 @@ GskRenderer *           gtk_root_get_renderer           (GtkRoot
 void                    gtk_root_get_surface_transform  (GtkRoot                *self,
                                                          int                    *x,
                                                          int                    *y);
+enum {
+  GTK_ROOT_PROP_FOCUS_WIDGET,
+  GTK_ROOT_NUM_PROPERTIES
+} GtkRootProperties;
+
+guint gtk_root_install_properties (GObjectClass *object_class,
+                                   guint         first_prop);
+
 G_END_DECLS
 
 #endif /* __GTK_ROOT_PRIVATE_H__ */