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Given a starting value and an ending value, QuickTime is able to figure out, for any moment in the duration of the animation, what the appropriate value between those two values should be. This process is called tweening, and the track that contains the information needed to do the tweening is called a .

QuickTime provides support for either simple linear interpolations of data or more complex tweening operations and operations. For instance, the various types of path tweens allow us to derive values based on the shape of an arbitrary curve defined by a vector path. And the list tween derives values from a list of atoms in an atom container, which can result in a series of discrete steps of non–continuous values. Anyway, QTPlugin currently supports only linear interpolations of numerical or graphical data.

The QTPlugin provides the developers with the Tween Framework to add tween–based animation to their applications. The Tween Framework, which is a set of classes, handles all the tasks necessary to provide tweening by using either or auto–running .

The QTPlgTween abstract class is part of the Tween Framework and defines the basic properties shared by any object that provides data for tweening.







The class has not constructor at all (you can always use the Realbasic common constructor syntax, of course, but you will obtain an usless object). Its destructor, will be implicitly invoked every time one of its derived classes will be destroyed.

specifies the index that identifies the current tween. This value is set automatically when appropriate
specifies the type of the tween in use. The type of data you can use to setup the tween depends on the value of this
specifies the offset and duration of the tweening operation. If you want the tweening operation to begin at some time after the start of a media sample or presentation, you can specify a non–0 value for the property of the object. This value should be expressed in the time scale appropriate for the destination (i.e. if the target is a this value should be secified in the media’s time scale). Similarly, to modify the duration of a tweening operation you can set the property of the object to a non–0 value
specifies the starting and ending values used during the tweening operation. The type of this data is determined by the and will be discussed in detail in the documentation regarding the QTPlgTween’s derived classes