DESCRIPTION

The Clutter::Alpha class binds together a Clutter::Timeline and a function. At each frame of the timeline, the Alpha object will call the given function, which will receive the value of the frame and must return a value between -1.0 and 2.0.

This is an example of a simple alpha function that increments linearly:

  sub linear {
      my ($alpha) = shift;

      return $alpha->get_timeline()->get_progress();
  }

A slightly more useful example:

  use Math::Trig;

  sub sine {
      my ($alpha) = @_;

      return sin($alpha->get_timeline()->get_progress() * pi);
  }

Instead of using real functions you can use a logical id for common easing functions, like: Clutter::LINEAR, Clutter::EASE_IN_CUBIC, Clutter::EASE_OUT_BOUNCE, etc. See Clutter::AnimationMode.

Alphas are used by Clutter::Behaviours and Clutter::Animationss to create implicit animations. By changing the alpha function inside a Clutter::Alpha object it's possible to change the progress of the animation.