How to rotate an object in Java 3D?

Question

I have a Cone I drew in Java 3D with the following code:

Cone cone = new Cone(2f, 3f);

Transform3D t3d = new Transform3D();
TransformGroup coneTransform = new TransformGroup(t3d);
coneTransform.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);

t3d.setTranslation(new Vector3f(0f,0f,0f);
coneTransform.setTransform(t3d);
coneTransform.addChild(cone);

this.addChild(coneTransform);

Suppose I have the cone sitting at point (1,1,1) and I want the tip of the cone to point down an imaginary line running through (0,0,0) and (1,1,1)... how can I do this?

Here's an example of what I've been trying:

Transform3D t3d = new Transform3D();  

Vector3f direction = new Vector3f(1,2,1);    

final double angleX = direction.angle(new Vector3f(1,0,0));
final double angleY = direction.angle(new Vector3f(0,1,0));
final double angleZ = direction.angle(new Vector3f(0,0,1));

t3d.rotX(angleX);
t3d.rotY(angleY);
t3d.rotZ(angleZ);

t3d.setTranslation(direction);

coneTransform.setTransform(t3d);

Thanks in advance for all help!

Answer 1

I'm just learning Java 3D myself at the moment, and from my current knowledge, the rotation methods set the transform to a rotation about that axis only. Therefore, if you wish to perform rotations about multiple axes, then you will need to use a second Transform3D.
ie:

Transform3D rotation = new Transform3D();
Transform3D temp = new Transform3D();

rotation.rotX(Math.PI/2);
temp.rotZ(Math.PI/2);
rotation.mul(temp); // multiply the 2 transformation matrices together.

As for the reason for Math.PI, this is because it uses radians instead of degrees, where Math.PI is equivalent to 180 degrees.

Finding the angle between your current orientation and your intended orientation isn't too hard - you could use Vector3fs, with the angle() method. A Vector would be set up with the initial orientation, and another in the intended. However, this doesn't tell you in which axes the angle lies. Doing so would require examination of the vectors to see which segments are set. [of course, there may be something that I am currently unaware of in the API]