68 lines
2.3 KiB
XML
68 lines
2.3 KiB
XML
<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">
|
|
<title>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>
|