Updating a 3D scene

Question

Hi All.....
I'm having trouble animating the movement of my particle, the following is my code with a loop that continuously changes the coordinates of the shape but doesn't update it, just shows its finishing point at the end of the loop....
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.event.*;
import java.awt.GraphicsConfiguration;
import com.sun.j3d.utils.geometry.Sphere;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.media.j3d.Shape3D;
import javax.vecmath.*;
import javax.vecmath.Vector3f;
public class p2 extends Applet
     private SimpleUniverse u = null;
     private Canvas3D c = null;
     public BranchGroup createSceneGraph(SimpleUniverse u)
          BranchGroup objRoot = new BranchGroup();
          Locale locale = new Locale(u);
          System.out.println("creating scene graph");
          TransformGroup objTrans = new TransformGroup();
          objTrans.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
          Transform3D t = new Transform3D();
     t.setScale(0.4);
     objTrans.setTransform(t);
          objRoot.addChild(objTrans);
          Color3f bgColor = new Color3f(0.0f, 0.0f, 0.0f);
          BoundingSphere bounds =
     new BoundingSphere(new Point3d(0.0,0.0,0.0), 100.0);
          Background bg = new Background(bgColor);
          bg.setApplicationBounds(bounds);
          objTrans.addChild(bg);
          int flags = GeometryArray.COORDINATES | GeometryArray.COLOR_4 | GeometryArray.NORMALS;
          IndexedQuadArray geom = new IndexedQuadArray(4, flags, 4);
          double[] coordinates = {
1.0, 1.0, 0,
1.0, -1.0, 0,
-1.0, -1.0, 0,
-1.0, 1.0, 0};
          int[] indices = { 0, 1, 2, 3 };
          geom.setCoordinates(0, coordinates);
          geom.setCoordinateIndices(0, indices);
          float[] colors = {
     1, 1, 1, 0,
     1, 0, 0, 1,
     1, 0, 1, 0,
     1, 1, 0, 0
          geom.setColors(0, colors);
          geom.setColorIndices(0, indices);
          float[] normal = { 0, 0, 1 };
          geom.setNormal(0, normal);
          geom.setNormal(1, normal);
          geom.setNormal(2, normal);
          geom.setNormal(3, normal);
          Appearance a = new Appearance();
PolygonAttributes pa = new PolygonAttributes();
          pa.setPolygonMode( PolygonAttributes.POLYGON_FILL);
pa.setCullFace( PolygonAttributes.CULL_NONE);
a.setPolygonAttributes( pa );
ColoringAttributes ca = new ColoringAttributes(0.4f, 1.0f, 0.1f, ColoringAttributes.SHADE_GOURAUD);
a.setColoringAttributes( ca );
Material mat = new Material();
mat.setAmbientColor(0.1f, 0.1f, 0.1f);
mat.setDiffuseColor(0.6f, 0.3f, 0.0f);
mat.setEmissiveColor(0.5f, 1.0f, 0.3f);
mat.setSpecularColor(1.0f, 1.0f, 1.0f);
mat.setShininess(120.0f);
a.setMaterial(mat);
TransparencyAttributes ta = new TransparencyAttributes(1, 0.5f); // this sets the transparency
ta.setTransparencyMode(ta.BLENDED);
a.setTransparencyAttributes(ta);
               double x = 0.05;
          for( int loop=0;loop<10;loop++)
               x = x + 0.05;
               double[] coordinates1 = {
               0.05+x, 0.05+x, 0,
0.05+x, -0.05+x, 0,
-0.05+x, -0.05+x, 0,
-0.05+x, 0.05+x, 0};
          geom.setCoordinates(0, coordinates1);
          Shape3D shape = new Shape3D(geom, a);
          draw(shape);
          objTrans.addChild(shape);
          objRoot.compile();
          return objRoot;
     public p2()
     public void init()
          setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
          Canvas3D c = new Canvas3D(config);
          add("Center", c);     
          u = new SimpleUniverse(c);
          BranchGroup scene = createSceneGraph(u);
u.getViewingPlatform().setNominalViewingTransform();
          u.addBranchGraph(scene);
          System.out.println("Finished init method. ");
public void destroy()
          u.removeAllLocales();

Answer 1

Use the Behavior framework to update your scene. Then scene updates are in sync with the rendering thread.
J3D use multiple threads for doing its job. One of the threads is the rendering loop. if you do changes in another thread as you do in your example, updates of your changes will be shown in the next rendering frame. If you change your scene too fast then it is possible that only the last state is rendered, because rendering a frame may take much longer then your loop.
However you need: single change step - render - single change step - render ... .
You can set up a Behavior which wakes up every frame. Rewrite your code so that a single change step is done (i.e remove the loop) every time the Behavior is called (this is done from the internal "Behavior"-thread and this thread is synced with the rendering thread) and put it into the appropriate method of the Behavior.