Positioning the Objects

So far, the examples have created objects in the same place, the center of the universe. In Java 3D, locations are described by using x, y, z coordinates. Increasing coordinates go along the x-axis to the right, along the y-axis upwards, and along the z-axis out of the screen. In the picture, x, y and z are represented by spheres, cones and cylinders.

This is called a "right-handed" coordinate system because the thumb and first two fingers of your right hand can be used to represent the three directions. All the distances are measured in meters.

To place your objects in the scene, you start at point (0,0,0), and then move the objects wherever you want. Moving the objects is called a "transformation", so the classes you use are: TransformGroup and Transform3D. You add both the object and the Transform3D to a TransformGroup before adding the TransformGroup to the rest of your scend

 

  1. Create a transform, a transform group and an object

Transform = new Transform3D();

transformGroup tg = new TransformGroup();

Cone cone = new Cone(0.5f, 0.5f);

  1. Specify a location for the object

Vector3f vector = new Vector3f(-.2f,.1f , -.4f);

  1. Set the transform to move (translate) the object to that location

Transform.setTranslation(vector);

  1. Add the transform to the transform group

tg.setTransform(transform);

  1. Add the object to the transform group

tg.addChild(cone);

This may seem complicated, but the transform groups enable you to collect objects together and move them as one unit. For example, a table could be made up of cylinders for legs and a box for the top. If you add all the parts of the table to a single transform group, you can move the whole table with one translation.

The Transform3D class can do much more than specifying the co-ordinates of the object. The functions include setScale to change the size of an object and rotX, rotY and rotZ for rotating an object around each axis (counter clockwise).

This example displays the different objects on each axis.

import com.sun.j3d.utils.geometry.*;

import com.sun.j3d.utils.universe.*;

import javax.media.j3d.*;

import javax.vecmath.*;

public class Position {

public Position() {

   SimpleUniverse universe = new SimpleUniverse();

   BranchGroup group = new BranchGroup();

   // X axis made of spheres

   for (float x = -1.0f; x <= 1.0f; x = x + 0.1f)

   {

      Sphere sphere = new Sphere(0.05f);

      TransformGroup tg = new TransformGroup();

      Transform3D transform = new Transform3D();

      Vector3f vector = new Vector3f( x, .0f, .0f);

      transform.setTranslation(vector);

      tg.setTransform(transform);

      tg.addChild(sphere);

      group.addChild(tg);

   }

   // Y axis made of cones

   for (float y = -1.0f; y <= 1.0f; y = y + 0.1f)

   {

      TransformGroup tg = new TransformGroup();

      Transform3D transform = new Transform3D();

      Cone cone = new Cone(0.05f, 0.1f);

      Vector3f vector = new Vector3f(.0f, y, .0f);

      transform.setTranslation(vector);

      tg.setTransform(transform);

      tg.addChild(cone);

      group.addChild(tg);

   }

   // Z axis made of cylinders

   for (float z = -1.0f; z <= 1.0f; z = z+ 0.1f)

   {

      TransformGroup tg = new TransformGroup();

      Transform3D transform = new Transform3D();

      Cylinder cylinder = new Cylinder(0.05f, 0.1f);

      Vector3f vector = new Vector3f(.0f, .0f, z);

      transform.setTranslation(vector);

      tg.setTransform(transform);

       tg.addChild(cylinder);

      group.addChild(tg);

   }

   Color3f light1Color = new Color3f(.1f, 1.4f, .1f); // green light

   BoundingSphere bounds =

      new BoundingSphere(new Point3d(0.0,0.0,0.0), 100.0);

   Vector3f light1Direction = new Vector3f(4.0f, -7.0f, -12.0f);

   DirectionalLight light1

      = new DirectionalLight(light1Color, light1Direction);

   light1.setInfluencingBounds(bounds);

   group.addChild(light1);

   universe.getViewingPlatform().setNominalViewingTransform();

   // add the group of objects to the Universe

   universe.addBranchGraph(group);

}

public static void main(String[] args) {

   System.setProperty("sun.awt.noerasebackground", "true");

   new Position();

}

}

Lighting up the World <<< Table of Contents >>> Appearance Is Everything