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13.1 The BehaviorTest example

There are occasions when the built−in behaviors do not provide enough functionality to capture the logic of your application. By creating your own classes derived from Behavior, you can easily integrate your application logic into Java 3D’s behavior processing framework.


The BehaviorTest example application uses four behaviors: the built−in RotationInterpolator and three custom behaviors of varying complexity: ObjectSizeBehavior, ExplodeBehavior, and StretchBehavior. See figure 13.1.

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Figure 13.1 The BehaviorTest example application. StretchBehavior is used to modify the geometry of the Sphere after every frame, while ObjectSizeBehavior reports the Bounds for the object after every 20 frames


ObjectSizeBehavior is the simplest, and it calculates the smallest BoundingBox that encloses a Shape3D’s geometry. The BoundingBox is recalculated every 20 frames, and the size of the BoundingBox is written to standard output. Note that the basic anatomy of a behavior described in section

11.3 is adhered to here.


ExplodeBehavior is more complex. Given a Shape3D object, it explodes the object after a specified number of milliseconds by rendering the Shape3D as points and modifying the coordinates within the Shape3D’s GeometryArray. The transparency of the object is gradually increased so that the object fades into the background.


StretchBehavior is the most complex of the custom behaviors. It operates upon a specified GeometryArray and animates the vertices within the array as if they were weights attached by springs to the origin. StretchBehavior listens for key presses and increases the acceleration of each vertex when a key is pressed. The increased acceleration causes the vertices to move away from the origin, which causes an increase in the restraining force from the spring. The vertices oscillate back and forth, finally coming to rest at their original position.