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javax.media.j3d
Class Behavior

java.lang.Object
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  +--javax.media.j3d.SceneGraphObject
        |
        +--javax.media.j3d.Node
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              +--javax.media.j3d.Leaf
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                    +--javax.media.j3d.Behavior
Direct Known Subclasses:
Billboard, Interpolator, LOD
public abstract class Behavior
extends Leaf

Behavior is an abstract class that contains the framework for all behavioral components in Java 3D. It contains a scheduling region and two methods: An initialization method, called once when the behavior becomes "live," and a processStimulus method called whenever appropriate by the Java 3D behavior scheduler. The Behavior object also contains the state information needed by its initialize * and processStimulus methods.

The scheduling region defines a spatial volume that serves to enable the scheduling of Behavior nodes. A Behavior node is active (can receive stimuli) whenever a ViewPlatform's activation volume intersects a Behavior object's scheduling region. Only active behaviors can receive stimuli.

The initialize method allows a Behavior object to initialize its internal state and specify its initial wakeup condition(s). Java 3D invokes a behavior's initialize code when the behavior's containing BranchGroup node is added to the virtual universe. Java 3D does not invoke the initialize method in a new thread. Thus, for Java 3D to regain control, the initialize method must not execute an infinite loop; it must return. Furthermore, a wakeup condition must be set or else the behavior's processStimulus method is never executed.

The processStimulus method receives and processes a behavior's ongoing messages. The Java 3D behavior scheduler invokes a Behavior node's processStimulus method when a ViewPlatform's activation volume intersects a Behavior object's scheduling region and all of that behavior's wakeup criteria are satisfied. The processStimulus method performs its computations and actions (possibly including the registration of state change information that could cause Java 3D to wake other Behavior objects), establishes its next wakeup condition, and finally exits.

Code Structure

When the Java 3D behavior scheduler invokes a Behavior object's processStimulus method, that method may perform any computation it wishes. Usually, it will change its internal state and specify its new wakeup conditions. Most probably, it will manipulate scene graph elements. However, the behavior code can only change those aspects of a scene graph element permitted by the capabilities associated with that scene graph element. A scene graph's capabilities restrict behavioral manipulation to those manipulations explicitly allowed.

The application must provide the Behavior object with references to those scene graph elements that the Behavior object will manipulate. The application provides those references as arguments to the behavior's constructor when it creates the Behavior object. Alternatively, the Behavior object itself can obtain access to the relevant scene graph elements either when Java 3D invokes its initialize method or each time Java 3D invokes its processStimulus method.

Behavior methods have a very rigid structure. Java 3D assumes that they always run to completion (if needed, they can spawn threads). Each method's basic structure consists of the following:

WakeupCondition Object

A WakeupCondition object is an abstract class specialized to fourteen different WakeupCriterion objects and to four combining objects containing multiple WakeupCriterion objects. A Behavior node provides the Java 3D behavior scheduler with a WakeupCondition object. When that object's WakeupCondition has been satisfied, the behavior scheduler hands that same WakeupCondition back to the Behavior via an enumeration.

WakeupCriterion Object

Java 3D provides a rich set of wakeup criteria that Behavior objects can use in specifying a complex WakeupCondition. These wakeup criteria can cause Java 3D's behavior scheduler to invoke a behavior's processStimulus method whenever

A Behavior object constructs a WakeupCriterion by constructing the appropriate criterion object. The Behavior object must provide the appropriate arguments (usually a reference to some scene graph object and possibly a region of interest). Thus, to specify a WakeupOnViewPlatformEntry, a behavior would specify the region that will cause the behavior to execute if a ViewPlatform enters it.

See Also:
WakeupCondition

Fields inherited from class javax.media.j3d.Node
ALLOW_AUTO_COMPUTE_BOUNDS_READ, ALLOW_AUTO_COMPUTE_BOUNDS_WRITE, ALLOW_BOUNDS_READ, ALLOW_BOUNDS_WRITE, ALLOW_COLLIDABLE_READ, ALLOW_COLLIDABLE_WRITE, ALLOW_LOCAL_TO_VWORLD_READ, ALLOW_PICKABLE_READ, ALLOW_PICKABLE_WRITE, ENABLE_COLLISION_REPORTING, ENABLE_PICK_REPORTING
 
Constructor Summary
Behavior()
          Constructs a Behavior node with default parameters.
 
Method Summary
 boolean getEnable()
          Retrieves the state of the Behavior enable flag.
 BoundingLeaf getSchedulingBoundingLeaf()
          Retrieves the Behavior node's scheduling bounding leaf.
 Bounds getSchedulingBounds()
          Retrieves the Behavior node's scheduling bounds.
protected  View getView()
          Returns the primary view associated with this behavior.
abstract  void initialize()
          Initialize this behavior.
 void postId(int postId)
          Post the specified Id.
abstract  void processStimulus(java.util.Enumeration criteria)
          Process a stimulus meant for this behavior.
 void setEnable(boolean state)
          Enables or disables this Behavior.
 void setSchedulingBoundingLeaf(BoundingLeaf region)
          Set the Behavior's scheduling region to the specified bounding leaf.
 void setSchedulingBounds(Bounds region)
          Set the Behavior's scheduling region to the specified bounds.
 void updateNodeReferences(NodeReferenceTable referenceTable)
          Callback used to allow a node to check if any scene graph objects referenced by that node have been duplicated via a call to cloneTree.
protected  void wakeupOn(WakeupCondition criteria)
          Defines this behavior's wakeup criteria.
 
Methods inherited from class javax.media.j3d.Node
cloneNode, cloneTree, cloneTree, cloneTree, cloneTree, cloneTree, cloneTree, duplicateNode, getBounds, getBoundsAutoCompute, getCollidable, getLocalToVworld, getLocalToVworld, getParent, getPickable, setBounds, setBoundsAutoCompute, setCollidable, setPickable
 
Methods inherited from class javax.media.j3d.SceneGraphObject
clearCapability, duplicateSceneGraphObject, getCapability, getUserData, isCompiled, isLive, setCapability, setUserData
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Behavior

public Behavior()
Constructs a Behavior node with default parameters. The default values are as follows:
Method Detail

initialize

public abstract void initialize()
Initialize this behavior. Classes that extend Behavior must provide their own initialize method.
NOTE: Applications should not call this method. It is called by the Java 3D behavior scheduler.

processStimulus

public abstract void processStimulus(java.util.Enumeration criteria)
Process a stimulus meant for this behavior. This method is invoked if the Behavior's wakeup criteria are satisfied and the ViewPlatform's activation region intersect with the Behavior's scheduling region. Classes that extend Behavior must provide their own processStimulus method.
NOTE: Applications should not call this method. It is called by the Java 3D behavior scheduler.
Parameters:
criteria - an enumeration of triggered wakeup criteria for this behavior

setSchedulingBounds

public void setSchedulingBounds(Bounds region)
Set the Behavior's scheduling region to the specified bounds. This is used when the scheduling bounding leaf is set to null.
Parameters:
region - the bounds that contains the Behavior's new scheduling region

getSchedulingBounds

public Bounds getSchedulingBounds()
Retrieves the Behavior node's scheduling bounds.
Returns:
this Behavior's scheduling bounds information

setSchedulingBoundingLeaf

public void setSchedulingBoundingLeaf(BoundingLeaf region)
Set the Behavior's scheduling region to the specified bounding leaf. When set to a value other than null, this overrides the scheduling bounds object.
Parameters:
region - the bounding leaf node used to specify the Behavior node's new scheduling region

getSchedulingBoundingLeaf

public BoundingLeaf getSchedulingBoundingLeaf()
Retrieves the Behavior node's scheduling bounding leaf.
Returns:
this Behavior's scheduling bounding leaf information

wakeupOn

protected void wakeupOn(WakeupCondition criteria)
Defines this behavior's wakeup criteria. This method may only be called from a Behavior object's initialize or processStimulus methods to (re)arm the next wakeup. It should be the last thing done by those methods.
Parameters:
criteria - the wakeup criteria for this behavior
Throws:
java.lang.IllegalStateException - if this method is called by a method other than initialize or processStimulus

postId

public void postId(int postId)
Post the specified Id. Behaviors use this method to cause sequential scheduling of other behavior object.
Parameters:
postId - the Id being posted

setEnable

public void setEnable(boolean state)
Enables or disables this Behavior. The default state is enabled.
Parameters:
state - true or false to enable or disable this Behavior

getEnable

public boolean getEnable()
Retrieves the state of the Behavior enable flag.
Returns:
the Behavior enable state

getView

protected View getView()
Returns the primary view associated with this behavior. This method is useful with certain types of behaviors (e.g., Billboard, LOD) that rely on per-View information and with behaviors in general in regards to scheduling (the distance from the view platform determines the active behaviors). The "primary" view is defined to be the first View attached to a live ViewPlatform, if there is more than one active View. So, for instance, Billboard behaviors would be oriented toward this primary view, in the case of multiple active views into the same scene graph.

updateNodeReferences

public void updateNodeReferences(NodeReferenceTable referenceTable)
Callback used to allow a node to check if any scene graph objects referenced by that node have been duplicated via a call to cloneTree. This method is called by cloneTree after all nodes in the sub-graph have been duplicated. The cloned Leaf node's method will be called and the Leaf node can then look up any object references by using the getNewObjectReference method found in the NodeReferenceTable object. If a match is found, a reference to the corresponding object in the newly cloned sub-graph is returned. If no corresponding reference is found, either a DanglingReferenceException is thrown or a reference to the original object is returned depending on the value of the allowDanglingReferences parameter passed in the cloneTree call.

NOTE: Applications should not call this method directly. It should only be called by the cloneTree method.

Overrides:
updateNodeReferences in class SceneGraphObject
Parameters:
referenceTable - a NodeReferenceTableObject that contains the getNewObjectReference method needed to search for new object instances.
See Also:
NodeReferenceTable, Node.cloneTree(), DanglingReferenceException
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