BoxStack.java

The main class for building a World where boxes are dropping on a flat surface. A SimpleSpace is attached for collision detection. The things to be implemented are HashSpace, box-box and box-plane collisions, and a Dantzig LCP constraint solver.

package simulator;

import javax.vecmath.*;
import java.awt.event.*;
import com.brackeen.javagamebook.input.*;
import java.util.List;
import java.util.LinkedList;


public class BoxStack
    extends Simulator {

  private class MyObject {
    Body body; // the body

    Geom geom; // geometries representing this body
  };

  private static final int NUM = 10;
  private static final double DENSITY = 5.0;
  private static final int MAX_CONTACTS = 4; // maximum number of contact points per body

  private static MyObject[] obj;
  private static int num = 0;
  private static int nextobj = 0;
  private static boolean random_pos = true;
  private static World world;
  private static Geom floor;

  private List contactgroup;

  protected GameAction fire

      = new GameAction("fire", GameAction.DETECT_INITAL_PRESS_ONLY);

  private class BoxStackCollision
      extends Collision implements ContactConstants {

    public void nearCallback(Geom g1, Geom g2) {

      // exit without doing anything if the two bodies are connected by a joint

      Body b1 = g1.getBody();
      Body b2 = g2.getBody();
      if (b1!=null && b2!=null &&
          b1.isConnectedExcluding(b2,"simulator.ContactJoint")) return;

      Contact[] contact = new Contact[MAX_CONTACTS]; // up to MAX_CONTACTS contacts per box-box

      for (int i = 0; i < MAX_CONTACTS; i++) {
        contact[i] = new Contact();
        contact[i].surface.mode = Bounce | SoftCFM;
        contact[i].surface.mu = Double.POSITIVE_INFINITY;
        contact[i].surface.mu2 = 0;
        contact[i].surface.bounce = 0.1;
        contact[i].surface.bounce_vel = 0.1;
        contact[i].surface.soft_cfm = 0.01;
      }
      int numc = collide(g1, g2, MAX_CONTACTS, contact);
      if (numc > 0) {
        for (int i = 0; i < numc; i++) {
          Joint c = new ContactJoint(world, contact[i]);
          c.attach(b1, b2);
        }
      }
    }
  }

  public static void main(String[] args) {
    new BoxStack().run();
  }

  public void start() {
    inputManager.mapToKey(fire, KeyEvent.VK_SPACE);
    inputManager.mapToMouse(fire, InputManager.MOUSE_BUTTON_1);

    world = new World();
    //space = new SimpleSpace(null);

    contactgroup = new LinkedList();
    obj = new MyObject[NUM];
    for (int i = 0; i < NUM; i++) {
      obj[i] = new MyObject();
    }

    world.setGravity(0, -0.5, 0);
    world.setCFM(1e-5);
    world.setAutoDisableFlag(true);
    world.setContactMaxCorrectingVel(0.1);
    world.setContactSurfaceLayer(0.001);

    floor = new Plane(space, 0, 1, 0, 0);
    space.setCollision(new BoxStackCollision());
  }

  public void step() {
    //floor.setState(Geom.STATE_IDLE);

    command();
    space.collide();
    world.step();
  }

  public void command() {
    int i;
    if (fire.isPressed()) {
      if (num < NUM) {
        i = num;
        num++;
      }
      else {
        i = nextobj;
        nextobj++;
        if (nextobj >= num) {
          nextobj = 0;
        }
      }
      obj[i].body = new Body(world);
      double[] sides = new double[3];
      for (int k = 0; k < 3; k++) {
        sides[k] = Math.random() * 50 + 10;
      }

      Matrix3d R = new Matrix3d();
      if (random_pos) {
        obj[i].body.setPosition(Math.random() * 20 - 100,
                                Math.random() + 200,
                                Math.random() * 20 - 200);
        R.set(new AxisAngle4d(Math.random() * 2.0 - 1.0,
                              Math.random() * 2.0 - 1.0,
                              Math.random() * 2.0 - 1.0,
                              Math.random() * 10.0 - 5.0));
      }
      else {
        double maxheight = 0;
        for (int k = 0; k < num; k++) {
          Vector3d pos = obj[k].body.getPosition();
          if (pos.z > maxheight) {
            maxheight = pos.z;
          }
        }
        obj[i].body.setPosition(0, maxheight + 1, 0);
        R.set(new AxisAngle4d(0, 1, 0, Math.random() * 10.0 - 5.0));
      }
      obj[i].body.setRotation(R);
      //dBodySetData (obj[i].body,(void*) i);

      Mass m = new Mass();
      m.setBox(DENSITY, sides[0], sides[1], sides[2]);
      obj[i].geom = new Box(space, sides[0], sides[1], sides[2]);
      obj[i].geom.setBody(obj[i].body);
      obj[i].body.setMass(m);
    }
  }
}