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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 QTPlgNumericalTween class is part of the Tween Framework and allows you to perform interpolation of numerical data. The type of the interpolated results depends on the object instantiated; note that the spin tween returns instead of numbers







The QTPlgNumericalTween class constructors are called when you create a new instance of the class, while the ˜QTPlgNumericalTween 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.


The class provides you with the following initializer methods:
(typeSelector as integer)
This is the default constructor. You specify the you want to instantiate by setting the typeSelector with one of the defined by the class
(other as QTPlgNumericalTween)
This is the copy constructor. The properties of the object to be copied will be used to initialize the new class instance properties

specifies the starting and ending values used during the tweening operation. This class accepts class instances as data sources. The initial value is specified by the property while the ending value is specified by the property. The type of the result of the tweening operation is determined by the value of the used during the class instantiation. If the actual object defines a spin tween, the property represents the initial rotation amount and the property the total number of rotations


the result of the numerical interpolation is a short integer
the result of the numerical interpolation is a long integer
the result of the numerical interpolation is a float
the result of the numerical interpolation is a double
the result of the numerical interpolation is a fixed long integer
the result of the numerical interpolation is a