[layout] Add LayoutManager::layout-changed signal

If a sub-class of LayoutManager wishes to implement a parametrized
layout policy it also needs a way to notify the container using the
layout manager that the layout has changed. We cannot do it directly
and automatically from the LayoutManager because a) it has no back
link to the actor that it is using it and b) it can be attached to
multiple actors.

This is a job for <cue raising dramatic music> signals!

By adding ClutterLayoutManager::layout-changed (and its relative
emitted function) we can notify actors using the layout manager that
the layout parameters have been changed, and thus they should queue
a relayout.

clutter/clutter-layout-manager.c

@@ -1,8 +1,42 @@
+/*
+ * Clutter.
+ *
+ * An OpenGL based 'interactive canvas' library.
+ *
+ * Copyright (C) 2009  Intel Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author:
+ *   Emmanuele Bassi <ebassi@linux.intel.com>
+ */
+
 /**
  * SECTION:clutter-layout-manager
  * @short_description: Layout managers base class
  *
- * #ClutterLayoutManager is FIXME
+ * #ClutterLayoutManager is a base abstract class for layout managers. A
+ * layout manager implements the layouting policy for a composite or a
+ * container actor: it controls the preferred size of the actor to which
+ * it has been paired, and it controls the allocation of its children.
+ *
+ * Any composite or container #ClutterActor subclass can delegate the
+ * layouting of its children to a #ClutterLayoutManager. Clutter provides
+ * a generic container using #ClutterLayoutManager called #ClutterBox.
+ *
+ * Clutter provides some simple #ClutterLayoutManager sub-classes, like
+ * #ClutterFixedLayout and #ClutterBinLayout.
  *
  * #ClutterLayoutManager is available since Clutter 1.2
  */
@@ -23,10 +57,19 @@
                    G_OBJECT_TYPE_NAME (_obj),                           \
                    (method));                           } G_STMT_END
 
+enum
+{
+  LAYOUT_CHANGED,
+
+  LAST_SIGNAL
+};
+
 G_DEFINE_ABSTRACT_TYPE (ClutterLayoutManager,
                         clutter_layout_manager,
                         G_TYPE_INITIALLY_UNOWNED);
 
+static guint manager_signals[LAST_SIGNAL] = { 0, };
+
 static void
 layout_manager_real_get_preferred_width (ClutterLayoutManager *manager,
                                          ClutterContainer     *container,
@@ -74,6 +117,45 @@ clutter_layout_manager_class_init (ClutterLayoutManagerClass *klass)
   klass->get_preferred_width = layout_manager_real_get_preferred_width;
   klass->get_preferred_height = layout_manager_real_get_preferred_height;
   klass->allocate = layout_manager_real_allocate;
+
+  /**
+   * ClutterLayoutManager::layout-changed:
+   * @manager: the #ClutterLayoutManager that emitted the signal
+   *
+   * The ::layout-changed signal is emitted each time a layout manager
+   * has been changed. Every #ClutterActor using the @manager instance
+   * as a layout manager should connect a handler to the ::layout-changed
+   * signal and queue a relayout on themselves:
+   *
+   * |[
+   *   static void layout_changed (ClutterLayoutManager *manager,
+   *                               ClutterActor         *self)
+   *   {
+   *     clutter_actor_queue_relayout (self);
+   *   }
+   *   ...
+   *     self->manager = g_object_ref_sink (manager);
+   *     g_signal_connect (self->manager, "layout-changed",
+   *                       G_CALLBACK (layout_changed),
+   *                       self);
+   * ]|
+   *
+   * Sub-classes of #ClutterLayoutManager that implement a layout that
+   * can be controlled or changed using parameters should emit the
+   * ::layout-changed signal whenever one of the parameters changes,
+   * by using clutter_layout_manager_layout_changed().
+   *
+   * Since: 1.2
+   */
+  manager_signals[LAYOUT_CHANGED] =
+    g_signal_new (I_("layout-changed"),
+                  G_TYPE_FROM_CLASS (klass),
+                  G_SIGNAL_RUN_LAST,
+                  G_STRUCT_OFFSET (ClutterLayoutManagerClass,
+                                   layout_changed),
+                  NULL, NULL,
+                  clutter_marshal_VOID__VOID,
+                  G_TYPE_NONE, 0);
 }
 
 static void
@@ -180,3 +262,22 @@ clutter_layout_manager_allocate (ClutterLayoutManager   *manager,
   klass = CLUTTER_LAYOUT_MANAGER_GET_CLASS (manager);
   klass->allocate (manager, container, allocation, flags);
 }
+
+/**
+ * clutter_layout_manager_layout_changed:
+ * @manager: a #ClutterLayoutManager
+ *
+ * Emits the #ClutterLayoutManager::layout-changed signal on @manager
+ *
+ * This function should only be called by implementations of the
+ * #ClutterLayoutManager class
+ *
+ * Since: 1.2
+ */
+void
+clutter_layout_manager_layout_changed (ClutterLayoutManager *manager)
+{
+  g_return_if_fail (CLUTTER_IS_LAYOUT_MANAGER (manager));
+
+  g_signal_emit (manager, manager_signals[LAYOUT_CHANGED], 0);
+}

clutter/clutter-layout-manager.h

@@ -1,3 +1,27 @@
+/*
+ * Clutter.
+ *
+ * An OpenGL based 'interactive canvas' library.
+ *
+ * Copyright (C) 2009  Intel Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author:
+ *   Emmanuele Bassi <ebassi@linux.intel.com>
+ */
+
 #if !defined(__CLUTTER_H_INSIDE__) && !defined(CLUTTER_COMPILATION)
 #error "Only <clutter/clutter.h> can be included directly."
 #endif
@@ -30,11 +54,23 @@ typedef struct _ClutterLayoutManagerClass       ClutterLayoutManagerClass;
  */
 struct _ClutterLayoutManager
 {
+  /*< private >*/
   GInitiallyUnowned parent_instance;
 };
 
 /**
  * ClutterLayoutManagerClass:
+ * @get_preferred_width: virtual function; override to provide a preferred
+ *   width for the layout manager. See also the get_preferred_width()
+ *   virtual function in #ClutterActor
+ * @get_preferred_height: virtual function; override to provide a preferred
+ *   height for the layout manager. See also the get_preferred_height()
+ *   virtual function in #ClutterActor
+ * @allocate: virtual function; override to allocate the children of the
+ *   layout manager. See also the allocate() virtual function in
+ *   #ClutterActor
+ * @layout_changed: class handler for the #ClutterLayoutManager::layout-changed
+ *   signal
  *
  * The #ClutterLayoutManagerClass structure contains only private
  * data and should be accessed using the provided API
@@ -43,8 +79,10 @@ struct _ClutterLayoutManager
  */
 struct _ClutterLayoutManagerClass
 {
+  /*< private >*/
   GInitiallyUnownedClass parent_class;
 
+  /*< public >*/
   void (* get_preferred_width)  (ClutterLayoutManager   *manager,
                                  ClutterContainer       *container,
                                  gfloat                  for_height,
@@ -60,6 +98,10 @@ struct _ClutterLayoutManagerClass
                                  const ClutterActorBox  *allocation,
                                  ClutterAllocationFlags  flags);
 
+  void (* layout_changed)       (ClutterLayoutManager   *manager);
+
+  /*< private >*/
+  /* padding for future expansion */
   void (* _clutter_padding_1) (void);
   void (* _clutter_padding_2) (void);
   void (* _clutter_padding_3) (void);
@@ -87,6 +129,8 @@ void clutter_layout_manager_allocate             (ClutterLayoutManager   *manage
                                                   const ClutterActorBox  *allocation,
                                                   ClutterAllocationFlags  flags);
 
+void clutter_layout_manager_layout_changed       (ClutterLayoutManager   *manager);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_LAYOUT_MANAGER_H__ */