Matthew Allum

mallum@openedhand.com

Clutter comes with a number of fairly generic prebuilt behaviour classes which provide a basis for transitions, animations and other visual effects. However even with the ability to combine a number of these behaviours sometimes they are not enough and a custom behaviour is needed to create a spcific animation. In order to implement a new #ClutterBehaviour subclass the usual machinery for subclassing a GObject should be used. The new subclass then just overides the ClutterBehaviour::alpha_notify() method. This method is passed an alpha_value which is then used to computer modifications to any actors the behaviour is applied to. This example demonstrates a behaviour that produces a vertical 'wipe' like affect by modifying the actors clip region static void clutter_behaviour_foo_alpha_notify (ClutterBehaviour *behaviour, guint32 alpha_value) { ClutterActor *actor gint i, n; gdouble factor; /* Normalise alpha value */ factor = (gdouble)alpha_value / CLUTTER_ALPHA_MAX_ALPHA; n = clutter_behaviour_get_n_actors (behaviour); /* Change clip height of each applied actor. Note usually better to use * clutter_behaviour_actors_foreach () for performance reasons. */ for (i=0; i<n; i++) { int clip_height; actor = clutter_behaviour_get_nth_actor (behaviour, i); clip_height = clutter_actor_get_height (actor) - (clutter_actor_get_height (actor) * factor); clutter_actor_set_clip (actor, 0, 0, clutter_actor_get_width (actor), clip_height); } }