69 lines
2.3 KiB
XML
69 lines
2.3 KiB
XML
<chapter id="creating-your-own-behaviours">
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<chapterinfo>
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<author>
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<firstname>Matthew</firstname>
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<surname>Allum</surname>
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<affiliation>
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<address>
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<email>mallum@openedhand.com</email>
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</address>
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</affiliation>
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</author>
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</chapterinfo>
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<title>Creating You Own Behaviours</title>
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<para>Clutter comes with a number of fairly generic prebuilt behaviour
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classes which provide a basis for transitions, animations and other
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visual effects. However even with the ability to combine a number of
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these behaviours sometimes they are not enough and a custom behaviour
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is needed to create a spcific animation.</para>
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<para>In order to implement a new #ClutterBehaviour subclass the usual
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machinery for subclassing a GObject should be used. The new subclass
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then just overides the #ClutterBehaviour::alpha_notify() method. This
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method is passed an alpha value which is then used to compute
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modifications to any actors the behaviour is applied to.</para>
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<example id="clutter-behaviour-alpha-notify-example">
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<title>Implementing the alpha-notify virtual function</title>
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<para>This example demonstrates a behaviour that produces a vertical
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'wipe' like affect by modifying the actors clip region</para>
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<programlisting>
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static void
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clutter_behaviour_foo_alpha_notify (ClutterBehaviour *behaviour,
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gdouble factor)
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{
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ClutterActor *actor
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gint i, n;
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n = clutter_behaviour_get_n_actors (behaviour);
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/* Change clip height of each applied actor. Note that it is
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* usually better to use clutter_behaviour_actors_foreach()
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* to avoid iterating multiple times
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*/
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for (i = 0; i < n; i++)
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{
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gfloat clip_height;
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actor = clutter_behaviour_get_nth_actor (behaviour, i);
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clip_height = clutter_actor_get_height (actor)
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- (clutter_actor_get_height (actor) * factor);
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clutter_actor_set_clip (actor,
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0,
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0,
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clutter_actor_get_width (actor),
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clip_height);
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}
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}
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</programlisting>
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</example>
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<para>If the new behaviour is meant to set an initial state on the
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actors to which its applied to, then the ClutterBehaviour::applied
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signal class handler should be overridden.</para>
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</chapter>
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