[JAVA3D] RotPosPathInterpolator causes NullPointerException

[David Ben-Yaacov]

Arrg!  I've been having trouble with this for a couple of days now, and would like to 
get some help, if you please.

I've created a method which creates a RotPosPathInterpolator behavior node and adds it 
to the scene graph.  When calling the method with the first TransformGroup, lets call 
it TransformGroup A, it works as expected.  When calling the method with another 
TransformGroup, lets call it TransformGroupB, there are problems.  As soon as the 
RotPosPathInterpolator  for TransformGroupB, gets added to the scene graph, a 
NullPointerException is thrown within a Java3D thread, as follows:

// Stack trace
java.lang.NullPointerException
 at 
javax.media.j3d.TransformGroupRetained.updateChildLocalToVworld(TransformGroupRetained.java:969)
 at 
javax.media.j3d.TransformGroupRetained.updateChildLocalToVworld(TransformGroupRetained.java:961)
 at 
javax.media.j3d.TransformGroupRetained.processChildLocalToVworld(TransformGroupRetained.java:825)
 at 
javax.media.j3d.TransformStructure.processCurrentLocalToVworld(TransformStructure.java:306)
 at javax.media.j3d.TransformStructure.processMessages(TransformStructure.java:186)
 at javax.media.j3d.StructureUpdateThread.doWork(StructureUpdateThread.java:83)
 at javax.media.j3d.J3dThread.run(J3dThread.java:250)
// end of stack trace

Here's the thread name where the NullPointerException occurred:
System Thread [J3D-TransformStructureUpdateThread-1]

The RotPosPathInterpolator's purpose is to move a TransformGroup a certain direction 
and to rotate it around to a certain angle.

Strangely, maybe 5% of the time, the NullPointerException does not occur, and 
TransformGroupB gets moved/rotated as expected.


Thank you very much,

David B


Here is most of the code:
                // x, y, z, and angle
                double[] delta = new double [] { 8d, 0d, 0d, -1*Math.PI };
  Alpha alpha = new Alpha(-1, 4000);


  double deltaAngle = delta[3];
  // Lets move back for the first 1/4 second,
  // and then fully rotate around for the next
  // 3/4 of a second, and then finish
  // the move the next 2 seconds
  float[] knots = new float[] { 0f, .25f / 3f, .25f, 1.0f };
  AxisAngle4f axisAngle;

  Quat4f[] quats = new Quat4f[4];
  quats[0] = new Quat4f();
  axisAngle = new AxisAngle4f();
  axisAngle.set(0f, 0f, 1f, 0f);
  quats[0].set(axisAngle);

  quats[1] = new Quat4f();
  axisAngle = new AxisAngle4f();
  axisAngle.set(0f, 0f, 1f, (float) deltaAngle/2f);
  quats[1].set(axisAngle);

  quats[2] = new Quat4f();
  axisAngle = new AxisAngle4f();
  axisAngle.set(0f, 0f, 1f, (float) deltaAngle);
  quats[2].set(axisAngle);

  quats[3] = new Quat4f();
  axisAngle = new AxisAngle4f();
  axisAngle.set(0f, 0f, 1f, (float) deltaAngle);
  quats[3].set(axisAngle);

  // The x-axis is the axis of transform
  Transform3D positionalDelta = new Transform3D();
  AxisAngle4f ang = new AxisAngle4f(1f, 0f, 1f, 0f);
  positionalDelta.set(ang);

  // The intermediate positions
  Point3f[] positions = new Point3f[4];
  positions[0] = new Point3f(0, 0, 0);
  positions[1] =
   new Point3f(
    (float) delta[0] * .25f,
    (float) delta[1] * .25f,
    (float) delta[2] * .25f);
  positions[2] =
   new Point3f(
    (float) delta[0] * .5f,
    (float) delta[1] * .5f,
    (float) delta[2] * .5f);
  positions[3] =
   new Point3f((float) delta[0], (float) delta[1], (float) delta[2]);


   RotPosPathInterpolator rotPathInterpolator =
    new RotPosPathInterpolator(
     alpha,
      unitBridge.getTransformGroup(),
     positionalDelta,
     knots,
     quats,
     positions);

  BoundingSphere bounds =
   new BoundingSphere(new Point3d(0, 0, 0), Double.MAX_VALUE);
  rotPathInterpolator.setSchedulingBounds(bounds);
  BranchGroup aBranchGroup = new BranchGroup();
  aBranchGroup.addChild(rotPathInterpolator);

  getBranchGraph().addChild(aBranchGroup);
  rotPathInterpolator.setEnable(true);

// END of Code snippet

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