constraint: Add ::update_allocation()

The Constraint should plug directly into the allocation mechanism, and
modify the allocation of the actor to which they are applied to. This is
similar to the mechanism used by the Effect class to modify the paint
sequence of an actor.

clutter/clutter-actor.c

@@ -1724,9 +1724,9 @@ clutter_actor_real_allocate (ClutterActor           *self,
   ClutterActorPrivate *priv = self->priv;
   gboolean x1_changed, y1_changed, x2_changed, y2_changed;
   gboolean flags_changed;
-  ClutterActorBox old = { 0, };
+  ClutterActorBox old_alloc = { 0, };
 
-  clutter_actor_store_old_geometry (self, &old);
+  clutter_actor_store_old_geometry (self, &old_alloc);
 
   x1_changed = priv->allocation.x1 != box->x1;
   y1_changed = priv->allocation.y1 != box->y1;
@@ -1749,11 +1749,11 @@ clutter_actor_real_allocate (ClutterActor           *self,
        * that wish to track the allocation flags
        */
       g_signal_emit (self, actor_signals[ALLOCATION_CHANGED], 0,
-                     box,
+                     &priv->allocation,
                      flags);
     }
 
-  clutter_actor_notify_if_geometry_changed (self, &old);
+  clutter_actor_notify_if_geometry_changed (self, &old_alloc);
 
   g_object_thaw_notify (G_OBJECT (self));
 }
@@ -4059,7 +4059,7 @@ clutter_actor_class_init (ClutterActorClass *klass)
   /**
    * ClutterActor:constraints:
    *
-   * Adds a #ClutterConstaint to the actor
+   * Adds a #ClutterConstraint to the actor
    *
    * Since: 1.4
    */
@@ -5279,6 +5279,7 @@ clutter_actor_allocate (ClutterActor           *self,
 {
   ClutterActorPrivate *priv;
   ClutterActorClass *klass;
+  ClutterActorBox alloc;
   gboolean child_moved;
 
   g_return_if_fail (CLUTTER_IS_ACTOR (self));
@@ -5292,8 +5293,22 @@ clutter_actor_allocate (ClutterActor           *self,
 
   priv = self->priv;
 
-  child_moved = (box->x1 != priv->allocation.x1 ||
-                 box->y1 != priv->allocation.y1);
+  alloc = *box;
+
+  if (priv->constraints != NULL)
+    {
+      const GList *constraints, *l;
+
+      constraints = _clutter_meta_group_peek_metas (priv->constraints);
+      for (l = constraints; l != NULL; l = l->next)
+        {
+          ClutterConstraint *constraint = l->data;
+          _clutter_constraint_update_allocation (constraint, self, &alloc);
+        }
+    }
+
+  child_moved = (alloc.x1 != priv->allocation.x1 ||
+                 alloc.y1 != priv->allocation.y1);
 
   /* If we get an allocation "out of the blue"
    * (we did not queue relayout), then we want to
@@ -5311,8 +5326,8 @@ clutter_actor_allocate (ClutterActor           *self,
   if (!priv->needs_allocation &&
       !(flags & CLUTTER_ABSOLUTE_ORIGIN_CHANGED) &&
       !child_moved &&
-      box->x2 == priv->allocation.x2 &&
-      box->y2 == priv->allocation.y2)
+      alloc.x2 == priv->allocation.x2 &&
+      alloc.y2 == priv->allocation.y2)
     {
       CLUTTER_NOTE (LAYOUT, "No allocation needed");
       return;
@@ -5330,7 +5345,7 @@ clutter_actor_allocate (ClutterActor           *self,
   CLUTTER_SET_PRIVATE_FLAGS (self, CLUTTER_IN_RELAYOUT);
 
   klass = CLUTTER_ACTOR_GET_CLASS (self);
-  klass->allocate (self, box, flags);
+  klass->allocate (self, &alloc, flags);
 
   CLUTTER_UNSET_PRIVATE_FLAGS (self, CLUTTER_IN_RELAYOUT);
 }

clutter/clutter-constraint.c

@@ -8,8 +8,10 @@
  * position or size.
  *
  * A #ClutterConstraint sub-class should contain the logic for modifying
- * the position or size of the #ClutterActor to which it is applied, using
- * the various signals and properties of #ClutterActor itself.
+ * the position or size of the #ClutterActor to which it is applied, by
+ * updating the actor's allocation. Each #ClutterConstraint can change the
+ * allocation of the actor to which they are applied by overriding the
+ * <function>update_allocation()</function> virtual function.
  *
  * #ClutterConstraint is available since Clutter 1.4
  */
@@ -20,18 +22,41 @@
 
 #include "clutter-constraint.h"
 
+#include "clutter-actor.h"
 #include "clutter-actor-meta-private.h"
 
 G_DEFINE_ABSTRACT_TYPE (ClutterConstraint,
                         clutter_constraint,
                         CLUTTER_TYPE_ACTOR_META);
 
+static void
+constraint_update_allocation (ClutterConstraint *constraint,
+                              ClutterActor      *actor,
+                              ClutterActorBox   *allocation)
+{
+}
+
 static void
 clutter_constraint_class_init (ClutterConstraintClass *klass)
 {
+  klass->update_allocation = constraint_update_allocation;
 }
 
 static void
 clutter_constraint_init (ClutterConstraint *self)
 {
 }
+
+void
+_clutter_constraint_update_allocation (ClutterConstraint *constraint,
+                                       ClutterActor      *actor,
+                                       ClutterActorBox   *allocation)
+{
+  g_return_if_fail (CLUTTER_IS_CONSTRAINT (constraint));
+  g_return_if_fail (CLUTTER_IS_ACTOR (actor));
+  g_return_if_fail (allocation != NULL);
+
+  CLUTTER_CONSTRAINT_GET_CLASS (constraint)->update_allocation (constraint,
+                                                                actor,
+                                                                allocation);
+}

clutter/clutter-constraint.h

@@ -69,6 +69,10 @@ struct _ClutterConstraintClass
   /*< private >*/
   ClutterActorMetaClass parent_class;
 
+  void (* update_allocation) (ClutterConstraint *constraint,
+                              ClutterActor      *actor,
+                              ClutterActorBox   *allocation);
+
   /*< private >*/
   void (* _clutter_constraint1) (void);
   void (* _clutter_constraint2) (void);

clutter/clutter-private.h

@@ -383,6 +383,10 @@ gint32 _clutter_backend_get_units_serial (ClutterBackend *backend);
 gboolean _clutter_effect_pre_paint  (ClutterEffect *effect);
 void     _clutter_effect_post_paint (ClutterEffect *effect);
 
+void _clutter_constraint_update_allocation (ClutterConstraint *constraint,
+                                            ClutterActor      *actor,
+                                            ClutterActorBox   *allocation);
+
 GType _clutter_layout_manager_get_child_meta_type (ClutterLayoutManager *manager);
 
 void     _clutter_event_set_platform_data (ClutterEvent       *event,