The progress function logical id - either a value from the #ClutterAnimationMode enumeration or a value returned by clutter_alpha_register_func().
If %CLUTTER_CUSTOM_MODE is used then the function set using clutter_alpha_set_closure() or clutter_alpha_set_func() will be used.
A #ClutterTimeline instance used to drive the alpha function.
The progress function logical id - either a value from the #ClutterAnimationMode enumeration or a value returned by clutter_alpha_register_func().
If %CLUTTER_CUSTOM_MODE is used then the function set using clutter_alpha_set_closure() or clutter_alpha_set_func() will be used.