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Collision Detection with Java3D - 2 E-mail
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This class demonstrates the use of the CollisionDetector class to perform processing when objects collide. When this program is run the white cube can be selected and moved by dragging on it with the right mouse button.


Image

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Frame;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Enumeration;

import javax.media.j3d.AmbientLight;
import javax.media.j3d.Appearance;
import javax.media.j3d.Behavior;
import javax.media.j3d.BoundingSphere;
import javax.media.j3d.Bounds;
import javax.media.j3d.BranchGroup;
import javax.media.j3d.Canvas3D;
import javax.media.j3d.DirectionalLight;
import javax.media.j3d.IndexedQuadArray;
import javax.media.j3d.Locale;
import javax.media.j3d.Material;
import javax.media.j3d.PhysicalBody;
import javax.media.j3d.PhysicalEnvironment;
import javax.media.j3d.Shape3D;
import javax.media.j3d.Transform3D;
import javax.media.j3d.TransformGroup;
import javax.media.j3d.View;
import javax.media.j3d.ViewPlatform;
import javax.media.j3d.VirtualUniverse;
import javax.media.j3d.WakeupCriterion;
import javax.media.j3d.WakeupOnCollisionEntry;
import javax.media.j3d.WakeupOnCollisionExit;
import javax.media.j3d.WakeupOnCollisionMovement;
import javax.media.j3d.WakeupOr;
import javax.vecmath.Color3f;
import javax.vecmath.Point3d;
import javax.vecmath.Point3f;
import javax.vecmath.Vector3d;
import javax.vecmath.Vector3f;

import com.sun.j3d.utils.picking.behaviors.PickTranslateBehavior;

/**
 * This class demonstrates the use of two collision detectors to overcome the
 * problem of an object colliding with more than one object at a time. The white
 * cube is movable by dragging it with the right mouse button.
 
 @see CollisionDetector2
 @author I.J.Palmer
 @version 1.0
 */
public class SimpleCollision2 extends Frame implements ActionListener {
  protected Canvas3D myCanvas3D = new Canvas3D(null);

  protected Button exitButton = new Button("Exit");

  protected BoundingSphere bounds = new BoundingSphere(new Point3d(0.00.0,
      0.0)100.0);

  /** Transform for the left cube. */
  protected TransformGroup leftGroup;

  /** Transform for the right cube */
  protected TransformGroup rightGroup;

  /**
   * Transform for the movable cube. This has read, write and pick reporting
   * capabilities enabled.
   */
  protected TransformGroup moveGroup;

  /** The left static cube. */
  protected Shape3D leftCube;

  /** The right static cube. */
  protected Shape3D rightCube;

  /** The movable cube that will collide with the other two cubes */
  protected Shape3D moveCube;

  /**
   * This builds the view branch of the scene graph.
   
   @return BranchGroup with viewing objects attached.
   */
  protected BranchGroup buildViewBranch(Canvas3D c) {
    BranchGroup viewBranch = new BranchGroup();
    Transform3D viewXfm = new Transform3D();
    viewXfm.set(new Vector3f(0.0f0.0f10.0f));
    TransformGroup viewXfmGroup = new TransformGroup(viewXfm);
    ViewPlatform myViewPlatform = new ViewPlatform();
    PhysicalBody myBody = new PhysicalBody();
    PhysicalEnvironment myEnvironment = new PhysicalEnvironment();
    viewXfmGroup.addChild(myViewPlatform);
    viewBranch.addChild(viewXfmGroup);
    View myView = new View();
    myView.addCanvas3D(c);
    myView.attachViewPlatform(myViewPlatform);
    myView.setPhysicalBody(myBody);
    myView.setPhysicalEnvironment(myEnvironment);
    return viewBranch;
  }

  /**
   * This adds some lights to the content branch of the scene graph.
   
   @param b
   *            The BranchGroup to add the lights to.
   */
  protected void addLights(BranchGroup b) {
    Color3f ambLightColour = new Color3f(0.5f0.5f0.5f);
    AmbientLight ambLight = new AmbientLight(ambLightColour);
    ambLight.setInfluencingBounds(bounds);
    Color3f dirLightColour = new Color3f(1.0f1.0f1.0f);
    Vector3f dirLightDir = new Vector3f(-1.0f, -1.0f, -1.0f);
    DirectionalLight dirLight = new DirectionalLight(dirLightColour,
        dirLightDir);
    dirLight.setInfluencingBounds(bounds);
    b.addChild(ambLight);
    b.addChild(dirLight);
  }

  /**
   * Creates the content branch of the scene graph.
   
   @return BranchGroup with content attached.
   */
  protected BranchGroup buildContentBranch() {
    //First create a different appearance for each cube
    Appearance app1 = new Appearance();
    Appearance app2 = new Appearance();
    Appearance app3 = new Appearance();
    Color3f ambientColour1 = new Color3f(1.0f0.0f0.0f);
    Color3f ambientColour2 = new Color3f(1.0f1.0f0.0f);
    Color3f ambientColour3 = new Color3f(1.0f1.0f1.0f);
    Color3f emissiveColour = new Color3f(0.0f0.0f0.0f);
    Color3f specularColour = new Color3f(1.0f1.0f1.0f);
    Color3f diffuseColour1 = new Color3f(1.0f0.0f0.0f);
    Color3f diffuseColour2 = new Color3f(1.0f1.0f0.0f);
    Color3f diffuseColour3 = new Color3f(1.0f1.0f1.0f);
    float shininess = 20.0f;
    app1.setMaterial(new Material(ambientColour1, emissiveColour,
        diffuseColour1, specularColour, shininess));
    app2.setMaterial(new Material(ambientColour2, emissiveColour,
        diffuseColour2, specularColour, shininess));
    app3.setMaterial(new Material(ambientColour3, emissiveColour,
        diffuseColour3, specularColour, shininess));

    //Build the vertex array for the cubes. We can use the same
    //data for each cube so we just define one set of data
    IndexedQuadArray indexedCube = new IndexedQuadArray(8,
        IndexedQuadArray.COORDINATES | IndexedQuadArray.NORMALS, 24);
    Point3f[] cubeCoordinates = new Point3f(1.0f1.0f1.0f),
        new Point3f(-1.0f1.0f1.0f),
        new Point3f(-1.0f, -1.0f1.0f),
        new Point3f(1.0f, -1.0f1.0f)new Point3f(1.0f1.0f, -1.0f),
        new Point3f(-1.0f1.0f, -1.0f),
        new Point3f(-1.0f, -1.0f, -1.0f),
        new Point3f(1.0f, -1.0f, -1.0f) };
    Vector3f[] cubeNormals = new Vector3f(0.0f0.0f1.0f),
        new Vector3f(0.0f0.0f, -1.0f),
        new Vector3f(1.0f0.0f0.0f),
        new Vector3f(-1.0f0.0f0.0f),
        new Vector3f(0.0f1.0f0.0f)new Vector3f(0.0f, -1.0f0.0f) };
    int cubeCoordIndices[] 012376540374562,
        10451673};
    int cubeNormalIndices[] 00001111222233,
        334444555};
    indexedCube.setCoordinates(0, cubeCoordinates);
    indexedCube.setNormals(0, cubeNormals);
    indexedCube.setCoordinateIndices(0, cubeCoordIndices);
    indexedCube.setNormalIndices(0, cubeNormalIndices);

    //Create the three cubes
    leftCube = new Shape3D(indexedCube, app1);
    rightCube = new Shape3D(indexedCube, app2);
    moveCube = new Shape3D(indexedCube, app3);

    //Define some user data so that we can print meaningful messages
    leftCube.setUserData(new String("left cube"));
    rightCube.setUserData(new String("right cube"));

    //Create the content branch and add the lights
    BranchGroup contentBranch = new BranchGroup();
    addLights(contentBranch);

    //Set up the transform to position the left cube
    Transform3D leftGroupXfm = new Transform3D();
    leftGroupXfm.set(new Vector3d(-1.50.00.0));
    leftGroup = new TransformGroup(leftGroupXfm);

    //Set up the transform to position the right cube
    Transform3D rightGroupXfm = new Transform3D();
    rightGroupXfm.set(new Vector3d(1.50.00.0));
    rightGroup = new TransformGroup(rightGroupXfm);

    //Create the movable cube's transform with a scale and
    //a translation. Set up the
    //capabilities so it can be moved by the behaviour
    Transform3D moveXfm = new Transform3D();
    moveXfm.set(0.7new Vector3d(0.02.01.0));
    moveGroup = new TransformGroup(moveXfm);
    moveGroup.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
    moveGroup.setCapability(TransformGroup.ALLOW_TRANSFORM_READ);
    moveGroup.setCapability(TransformGroup.ENABLE_PICK_REPORTING);
    //Create the behaviour to move the movable cube
    PickTranslateBehavior pickTranslate = new PickTranslateBehavior(
        contentBranch, myCanvas3D, bounds);
    contentBranch.addChild(pickTranslate);

    //Create and add the two colision detectors
    CollisionDetector2 myColDetLeft = new CollisionDetector2(leftCube,
        bounds);
    contentBranch.addChild(myColDetLeft);
    CollisionDetector2 myColDetRight = new CollisionDetector2(rightCube,
        bounds);
    contentBranch.addChild(myColDetRight);

    //Set up the scene graph
    contentBranch.addChild(moveGroup);
    contentBranch.addChild(leftGroup);
    contentBranch.addChild(rightGroup);
    moveGroup.addChild(moveCube);
    leftGroup.addChild(leftCube);
    rightGroup.addChild(rightCube);

    return contentBranch;

  }

  /** Process exit button's action to quit */
  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == exitButton) {
      dispose();
      System.exit(0);
    }
  }

  public SimpleCollision2() {
    VirtualUniverse myUniverse = new VirtualUniverse();
    Locale myLocale = new Locale(myUniverse);
    myLocale.addBranchGraph(buildViewBranch(myCanvas3D));
    myLocale.addBranchGraph(buildContentBranch());
    setTitle("SimpleWorld");
    setSize(400400);
    setLayout(new BorderLayout());
    Panel bottom = new Panel();
    bottom.add(exitButton);
    add(BorderLayout.CENTER, myCanvas3D);
    add(BorderLayout.SOUTH, bottom);
    exitButton.addActionListener(this);
    setVisible(true);
  }

  public static void main(String[] args) {
    SimpleCollision2 sw = new SimpleCollision2();
  }
}

/**
 * A simple collision detector class. This responds to a collision event by
 * printing a message with information about the type of collision event and the
 * object involved. This is a variation of the CollisionDetector class that
 * prints information about the object that is associated with this behaviour
 * rather than the object that has been collided with. An example of its use is
 * given in the SimpleCollision2 class.
 
 @author I.J.Palmer
 @version 1.0
 @see CollisionDetector
 @see SimpleCollision2
 */class CollisionDetector2 extends Behavior {
  /** The shape that is being watched for collisions. */
  protected Shape3D collidingShape;

  /** The separate criteria that trigger this behaviour */
  protected WakeupCriterion[] theCriteria;

  /** The result of the 'OR' of the separate criteria */
  protected WakeupOr oredCriteria;

  /**
   @param theShape
   *            Shape3D that is to be watched for collisions.
   @param theBounds
   *            Bounds that define the active region for this behaviour
   */
  public CollisionDetector2(Shape3D theShape, Bounds theBounds) {
    collidingShape = theShape;
    setSchedulingBounds(theBounds);
  }

  /**
   * This sets up the criteria for triggering the behaviour. It creates an
   * entry, exit and movement trigger, OR's these together and then sets the
   * OR'ed criterion as the wake up condition.
   */
  public void initialize() {
    theCriteria = new WakeupCriterion[3];
    WakeupOnCollisionEntry startsCollision = new WakeupOnCollisionEntry(
        collidingShape);
    WakeupOnCollisionExit endsCollision = new WakeupOnCollisionExit(
        collidingShape);
    WakeupOnCollisionMovement moveCollision = new WakeupOnCollisionMovement(
        collidingShape);
    theCriteria[0= startsCollision;
    theCriteria[1= endsCollision;
    theCriteria[2= moveCollision;
    oredCriteria = new WakeupOr(theCriteria);
    wakeupOn(oredCriteria);
  }

  /**
   * This is where the work is done. This identifies the type of collision
   * (entry, exit or movement) and prints a message stating that an object has
   * collided with this object. The userData field of the shape associated
   * with this collision detector # is used to identify the object. Finally,
   * the wake up condition is set to be the OR'ed criterion again.
   */
  public void processStimulus(Enumeration criteria) {
    while (criteria.hasMoreElements()) {
      WakeupCriterion theCriterion = (WakeupCriterioncriteria
          .nextElement();
      if (theCriterion instanceof WakeupOnCollisionEntry) {
        System.out.println("Collided with "
            + collidingShape.getUserData());
      else if (theCriterion instanceof WakeupOnCollisionExit) {
        System.out.println("Stopped colliding with  "
            + collidingShape.getUserData());
      else {
        System.out.println("Moved whilst colliding with "
            + collidingShape.getUserData());
      }
    }
    wakeupOn(oredCriteria);
  }
}

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