Clutter provides several effects functions that can be used together with a timeline to change the properties of a single actor over time, using a simple numeric calculation. In many cases this is an easier way to implement animation. For instance, clutter_effect_fade() gradually changes the opacity of an actor or clutter_effect_rotate_x() gradually changes the rotation of an actor, calculating the opacity or rotation by calling the supplied alpha callback.

To use a clutter effect, you should first create a ClutterEffectTemplate, specifying your timeline object and a ClutterAlphaFunc callback. This callback will need to call clutter_alpha_get_timeline() so it can return a value based on the timeline's current frame number and total number of frames, using clutter_timeline_get_current_frame() and clutter_timeline_get_n_frames(). The result should be between 0 and CLUTTER_ALPHA_MAX, with the meaning of the result depending on the effect used. For instance, CLUTTER_ALPHA_MAX would be 100% opacity when using clutter_effect_fade(). Several built-in callbacks, such as CLUTTER_ALPHA_SINE, allow you to easily specify natural movement.

You should then provide this ClutterEffectTemplate to one of the clutter_effect functions, along with the actor and any extra parameters required by that function. Remember to unref the effect template after providing it to the effect function (which will take a reference). Unlike actors, these do not have "floating references".

To make it easier to use different timelines with different effects, you can use clutter_effect_template_set_timeline_clone() to cause the effect to clone (copy instead of just referencing) the timeline, allowing you to change the original timeline and supply it to a second effect, without influencing the first effect.

The effects API is actually a simplified API that wraps the ClutterBehaviour objects. However, the effect functions can only control one actor at a time and do not allow you to change the effects while the timeline is running. To do this you can use the behaviours directly, as described in the Behaviours section.

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