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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 presentations.

The QTPlgTweenPlay class is part of the Tween Framework and allows you to run and inspect the result of a tweening operation without creating a .







The QTPlgTweenPlay class constructors are called when you create a new instance of the class, while the ˜QTPlgTweenPlay class destructor, is called automatically when the class is no more in use. Also, you can invoke the class destructor by setting the instance of the class to nil.

Once a new class instance is returned, it is good practice to check the class property to be sure that the new object can be used. A QTPlgTweenPlay presentation is valid if you have specified valid during its inizialization.


The class provides you with the following initializer methods:
(source as , [timeScale as integer])
This is the class initializer. You specify the starting and ending values of the tweening operation by using the source parameter; also, you will use the to indicate the duration of the presentation by setting the value of the class property. Finally you determines the time scale of the presentation by using the optional parameter timeScale; if you omit this parameter, a default value of 600 will be used

specifies the result of the current tweening operation at a given time. The type of object returned depends on the type of the tweened data. If the tween specify a and the aspected result is a number, the object returned is a instance with the and the properties set to the same value. On the other hand, if the result of the tweening operation is a graphical object this property is set with an appropriate QTPlugin graphics object. You can find more informations about the result of tweening consulting the section regarding the constant values to be used to specify different kind of tweens present in the documentation of every QTPlgTween derived class. The value of this property is updated every time a presentation is