src/edu/mit/ezyang/gravity/j3d/behaviors/PhysicsBehavior.java

   1 package edu.mit.ezyang.gravity.j3d.behaviors;
   2
   3 import edu.mit.ezyang.gravity.GravitySimulatorView;
   4 import edu.mit.ezyang.gravity.actors.Body;
   5 import edu.mit.ezyang.gravity.j3d.EditableGroup;
   6 import java.util.Enumeration;
   7 import javax.media.j3d.Behavior;
   8 import javax.media.j3d.Node;
   9 import javax.media.j3d.Transform3D;
  10 import javax.media.j3d.TransformGroup;
  11 import javax.media.j3d.WakeupOnElapsedTime;
  12 import javax.vecmath.Vector3f;
  13
  14 /**
  15  *
  16  * @author Edward Z. Yang <ezyang@mit.edu>
  17  */
  18 public class PhysicsBehavior extends Behavior {
  19     protected TransformGroup targetTG;
  20     protected GravitySimulatorView view;
  21     protected int interval = 10;
  22     static public float G = .01f;
  23     public PhysicsBehavior(TransformGroup tg, GravitySimulatorView view) {
  24         this.targetTG = tg;
  25         // Yeah, I know this is very hacky. We need to separate out the
  26         // rendering components from the GUI view class
  27         this.view = view;
  28     }
  29     public void initialize() {
  30         this.wakeupOn(new WakeupOnElapsedTime(interval));
  31     }
  32     public void processStimulus(Enumeration criteria) {
  33         if (targetTG.getChild(0) instanceof Body) {
  34             Body body = (Body) targetTG.getChild(0);
  35             Transform3D transform = new Transform3D();
  36             targetTG.getTransform(transform);
  37             Vector3f trans = new Vector3f();
  38             transform.get(trans);
  39             // velocity modifications from force
  40             if (body.mass != 0f) {
  41                 Enumeration<Node> children = view.universeRoot.getAllChildren();
  42                 while (children.hasMoreElements()) {
  43                     Node node = children.nextElement();
  44                     if (node instanceof EditableGroup) {
  45                         TransformGroup group = ((EditableGroup) node).getTransformGroup();
  46                         Node subnode = group.getChild(0);
  47                         if (subnode instanceof Body) {
  48                             // ok, this can affect our dude
  49                             Body otherBody = (Body) subnode;
  50                             if (otherBody == body) continue;
  51                             // disregard massless objects
  52                             if (otherBody.mass == 0) continue;
  53                             Transform3D otherTransform = new Transform3D();
  54                             group.getTransform(otherTransform);
  55                             Vector3f otherVector = new Vector3f();
  56                             otherTransform.get(otherVector);
  57                             otherVector.sub(trans);
  58                             float distance = Math.abs(otherVector.length());
  59                             if (distance == 0f) continue;
  60                             float force = G * otherBody.mass * body.mass / (distance * distance);
  61                             float accel = force / body.mass;
  62                             otherVector.normalize();
  63                             otherVector.scale(accel);
  64                             body.velocity.add(otherVector);
  65                             if (body == view.selectedPrimitive) {
  66                                 view.notifyPick(body);
  67                             }
  68                         }
  69                     }
  70                 }
  71             }
  72
  73             // now redraw the object
  74             if (body.velocity.length() != 0f) {
  75                 trans.x += body.velocity.x / 1000 * interval;
  76                 trans.y += body.velocity.y / 1000 * interval;
  77                 trans.z += body.velocity.z / 1000 * interval;
  78                 transform.set(trans, 1.0f);
  79                 targetTG.setTransform(transform);
  80                 postId(1);
  81             }
  82         }
  83         this.wakeupOn(new WakeupOnElapsedTime(interval));
  84     }
  85 }