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The Java 3D API allows you to develop 3D graphics applications that have a high degree of visual realism. In this, we will be using the concept of scene graph. This scene graph is structured as a tree containing several elements that are necessary to display the objects.
Before proceeding, I would like to review some of the basic concepts of 3D. In a three-dimensional coordinate (x,y,z), the z component specifies distance from the viewer. Java 3D uses z values to remove nonvisible surfaces of distance obscured objects. Let us look at an example.
Figure 1: Shows the image of torus for understanding the concept of 3D.
Now in the above figure, the z values of the red torus in figure 1 are small because it is close to the viewer. It will obscure portions of the blue torus when the z values of both tori are compared during rendering.
Now, what are 3D objects? A 3D object contains a collection of coordinates rendered together. The Primitive class is an abstract class for geometry objects that can be used as simple building blocks in your scene graph. Java 3D includes four useful concrete subclasses of Primitive — Sphere, Box, Cone, and Cylinder — that allow you to easily create basic objects without having to specify a lot of data. Material properties also play a significant role in this.
Material properties describe how an object reflects light. If the object (Primitive or Shape3D) does not have a Material object in its Appearance object, it will not be illuminated even though you are specifying a light source. So, the user must create a Material object, enable lighting in the Material object, and add the Material object to the Appearance object.
Now we will go through the concept of 3D scenes. A Java 3D scene graph is a tree with two parts or branches. They are as follows:
For most simple applications, we can use the universe utility classes; the most interesting of which is SimpleUniverse class.
Listing 1: Shows the code of generating a scene graph with the cylinders that make up axis and three cones.
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.event.*;
import java.awt.*;
import java.awt.GraphicsConfiguration;
import com.sun.j3d.utils.applet.MainFrame;
import com.sun.j3d.utils.geometry.*;
import com.sun.j3d.utils.universe.*;
import javax.media.j3d.*;
import javax.vecmath.*;
import com.sun.j3d.utils.behaviors.vp.*;
public class TransformOrder extends Applet {
public static final int X =1;
public static final int Y =2;
public static final int Z =3;
public static final int ROTATE_TOP =4;
public static final int TRANSLATE_TOP =5;
public static final int NO_TRANSFORM =6;
private SimpleUniverse universe ;
private BranchGroup scene;
private Canvas3D canvas;
private BoundingSphere bounds =
new BoundingSphere(new Point3d(0.0, 0.0, 0.0), 1000.0);
private Appearance red = new Appearance();
private Appearance yellow = new Appearance();
private Appearance purple = new Appearance();
Transform3D rotate = new Transform3D();
Transform3D translate = new Transform3D();
public void setupView() {
/** Add some view related things to view branch side
of scene graph */
// add mouse interaction to the ViewingPlatform
OrbitBehavior orbit = new OrbitBehavior(canvas,
OrbitBehavior.REVERSE_ALL|OrbitBehavior.STOP_ZOOM);
orbit.setSchedulingBounds(bounds);
ViewingPlatform viewingPlatform = universe.getViewingPlatform();
// This will move the ViewPlatform back a bit so the
// objects in the scene can be viewed.
viewingPlatform.setNominalViewingTransform();
viewingPlatform.setViewPlatformBehavior(orbit);
}
//construct each branch of the graph, changing the order children added
// since Group node can only have one parent, have to construct
// new translate and rotate group nodes for each branch.
Group rotateOnTop(){
Group root=new Group();
TransformGroup objRotate = new TransformGroup(rotate);
TransformGroup objTranslate = new TransformGroup(translate);
Cone redCone=
new Cone(.3f, 0.7f, Primitive.GENERATE_NORMALS, red);
root.addChild(objRotate);
objRotate.addChild(objTranslate);
objTranslate.addChild(redCone); //tack on red cone
return root;
}
Group translateOnTop(){
Group root=new Group();
TransformGroup objRotate = new TransformGroup(rotate);
TransformGroup objTranslate = new TransformGroup(translate);
Cone yellowCone=
new Cone(.3f, 0.7f, Primitive.GENERATE_NORMALS, yellow);
root.addChild(objTranslate);
objTranslate.addChild(objRotate);
objRotate.addChild(yellowCone); //tack on yellow cone
return root;
}
Group noTransform(){
Cone purpleCone=
new Cone(.3f, 0.7f, Primitive.GENERATE_NORMALS, purple);
return purpleCone;
}
/** Represent an axis using cylinder Primitive. Cylinder is
aligned with Y axis, so we have to rotate it when
creating X and Z axis
*/
public TransformGroup createAxis(int type) {
//appearance and lightingProps are used in
//lighting. Each axis a different color
Appearance appearance = new Appearance();
Material lightingProps = new Material();
Transform3D t = new Transform3D();
switch (type) {
case Z:
t.rotX(Math.toRadians(90.0));
lightingProps.setAmbientColor(1.0f,0.0f,0.0f);
break;
case Y:
// no rotation needed, cylinder aligned with Y already
lightingProps.setAmbientColor(0.0f,1.0f,0.0f);
break;
case X:
t.rotZ(Math.toRadians(90.0));
lightingProps.setAmbientColor(0.0f,0.0f,1.0f);
break;
default:
break;
}
appearance.setMaterial(lightingProps);
TransformGroup objTrans = new TransformGroup(t);
objTrans.addChild( new Cylinder(.03f,2.5f,Primitive.GENERATE_NORMALS,appearance));
return objTrans;
}
/** Create X, Y , and Z axis, and 3 cones. Throws in
some quick lighting to help viewing the scene
*/
public BranchGroup createSceneGraph() {
// Create the root of the branch graph
BranchGroup objRoot = new BranchGroup();
//45 degree rotation around the X axis
rotate.rotX(Math.toRadians(45.0));
//translation up the Y axis
translate.setTranslation(new Vector3f(0.0f,2.0f,1.0f)); //SCD 0.0f));
//Material objects are related to lighting, we'll cover
//that later
Material redProps = new Material();
redProps.setAmbientColor(1.0f,0.0f,0.0f); //red cone
red.setMaterial(redProps);
Material yellowProps = new Material();
yellowProps.setAmbientColor(1.0f,1.0f,0.0f); //yellow cone
yellow.setMaterial(yellowProps);
Material purpleProps = new Material();
purpleProps.setAmbientColor(0.8f,0.0f,0.8f); //purple cone
purple.setMaterial(purpleProps);
// Create a x,y,z axis, and then 3 cone branches
objRoot.addChild(createAxis(X));
objRoot.addChild(createAxis(Y));
objRoot.addChild(createAxis(Z));
objRoot.addChild(noTransform()); //purple cone
objRoot.addChild(rotateOnTop()); //red cone
objRoot.addChild(translateOnTop()); //yellow cone
//throw in some light so we aren't stumbling
//around in the dark
Color3f lightColor = new Color3f(.3f,.3f,.3f);
AmbientLight ambientLight= new AmbientLight(lightColor);
ambientLight.setInfluencingBounds(bounds);
objRoot.addChild(ambientLight);
DirectionalLight directionalLight = new DirectionalLight();
directionalLight.setColor(lightColor);
directionalLight.setInfluencingBounds(bounds);
objRoot.addChild(directionalLight);
return objRoot;
}
public TransformOrder() {
}
public void init() {
BranchGroup scene = createSceneGraph();
setLayout(new BorderLayout());
GraphicsConfiguration config =
SimpleUniverse.getPreferredConfiguration();
canvas = new Canvas3D(config);
add("Center", canvas);
// Create a simple scene and attach it to the virtual universe
universe = new SimpleUniverse(canvas);
setupView();
universe.addBranchGraph(scene);
}
public void destroy() {
universe.removeAllLocales();
}
//
// The following allows TransformOrder to be run as an application
// as well as an applet
//
public static void main(String[] args) {
new MainFrame(new TransformOrder(), 256, 256);
}
}In the above coding, we have explained the concept of generating a scene graph with the cylinders that make up the axis and three cones. Then it adds one cone with rotate before translate and another that has translate before rotate.
So, in this article on JAVA 3D, we have learnt something new about JAVA. We have learnt to create 3D graphic application. Along with that, we also learnt about some of the basic concepts of 3D drawing.
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