Matthew
Allum
mallum@openedhand.com
Creating You Own Behaviours
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 compute
modifications to any actors the behaviour is applied to.
Implementing the alpha-notify virtual function<title>
<para>This example demonstrates a behaviour that produces a vertical
'wipe' like affect by modifying the actors clip region</para>
<programlisting>
static void
clutter_behaviour_foo_alpha_notify (ClutterBehaviour *behaviour,
gdouble factor)
{
ClutterActor *actor
gint i, n;
n = clutter_behaviour_get_n_actors (behaviour);
/* Change clip height of each applied actor. Note that it is
* usually better to use clutter_behaviour_actors_foreach()
* to avoid iterating multiple times
*/
for (i = 0; i < n; i++)
{
gfloat 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);
}
}
</programlisting>
</example>
<para>If the new behaviour is meant to set an initial state on the
actors to which its applied to, then the ClutterBehaviour::applied
signal class handler should be overridden.</para>
</chapter>