mutter/doc/reference/clutter/creating-your-own-behaviours.sgml

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<chapter id="creating-your-own-behaviours">
<chapterinfo>
<author>
<firstname>Matthew</firstname>
<surname>Allum</surname>
<affiliation>
<address>
<email>mallum@openedhand.com</email>
</address>
</affiliation>
</author>
</chapterinfo>
<title>Creating You Own Behaviours</title>
<para>
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.
</para>
<para>
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.
</para>
<example id="clutter-behaviour-alpha-notify-example">
<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,
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&lt;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);
}
}
</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>