predatorbehavior.java

一个模拟鸟群飞行的3D程序

// PredatorBehavior.java
// Andrew Davison, April 2005, [e-mail]
// Sirinart Sakarin, March 2003, [e-mail]

/* PredatorBehavior maintains its own BoidsList of Boids, _and_ a
   reference to the prey BoidsList. The list is obtained via a reference
   to the PreyBehavior object.

   PredatorBehavior initialises its BoidsList of Boids and the 
   BranchGroup of Boid BranchGroup nodes.

   PredatorBehavior maintains one extra velocity rule: findClosePrey()
    - if the predator is hungry then it looks for nearby prey to eat
   This method is called by each PredatorBoid object.

   There is also an eatClosePrey() method which is called by PredatorBoid
   to actual eat PreyBoid if one (or more) is sufficiently close.
*/

import java.util.*;
import javax.media.j3d.*;
import javax.vecmath.*;


public class PredatorBehavior extends FlockBehavior
{
  // scaling factor for the velocity calculated by findClosePrey() rule
  private final static float FIND_WEIGHT = 0.2f;
  
  private BoidsList preyList;
  private PreyBehavior preyBeh;

  // used for repeated calculations
  private Vector3f preyPos = new Vector3f();
  private Vector3f distFrom = new Vector3f();
  

  public PredatorBehavior(int numBoids, Obstacles obs)
  {
    super(numBoids);
    System.out.println("Num. Predators: " + numBoids);
    createBoids(numBoids, obs);
  }


  private void createBoids(int numBoids, Obstacles obs)
  /* Initialise the Boidslist of PredatorBoid objects and add
     the TransformGroups for these boids to boidsBG.
     Boid is a subclass of TransformGroup so can be added to boidsBG
     directly.
  */
  { PredatorBoid pb; 
	for(int i=0; i < numBoids; i++){
      pb = new PredatorBoid(obs, this);
	  boidsBG.addChild(pb);    // add to BranchGroup
	  boidsList.add(pb);       // add to BoidsList
    }
    boidsBG.addChild(this);    // store the pred. behaviour with its BG
  } // end of createBoids()


  public void setPreyBeh(PreyBehavior pb)
  // store the prey's behavior
  { preyBeh = pb; }


  public int eatClosePrey(Vector3f boidPos)
  /* Find a nearby PreyBoid (or PreyBoids) and eat it. 
     This causes the PreyBoid to be detached from the scene
     and from its BoidsList.
     Return the number of prey eaten (usually 1 or 0).
     Called by animateBoid() in PredatorBoid.
  */
  { preyList = preyBeh.getBoidsList();
    int numPrey = preyList.size();
    int numEaten = 0;
    PreyBoid b;

    int i = 0;
	while((b = (PreyBoid)preyList.getBoid(i)) != null) {
      distFrom.set(boidPos);
      distFrom.sub( b.getBoidPos() );
	  if(distFrom.length() < PROXIMITY/3.0) {   // is boid v.close to the prey
		preyBeh.eatBoid(i);   // found prey, so eat it
        numPrey--;
        numEaten++;
	    System.out.println("numPrey: " + numPrey);
      }
      else 
        i++;
	}
    return numEaten;
  } // end of eatClosePrey()



  public Vector3f findClosePrey(Vector3f boidPos)
  /* Find all the nearby prey, then move towards their average
     position by a scaled amount.

     This is an extra velocity rule used by each PredatorBoid.
     Called by doVelocityRules() in PredatorBoid.
  */
  { preyList = preyBeh.getBoidsList();  // get prey list
    int numClosePrey = 0;
    preyPos.set(0,0,0);
    Vector3f pos;
    PreyBoid b;

    int i = 0;
	while((b = (PreyBoid)preyList.getBoid(i)) != null) {
      pos = b.getBoidPos();
      distFrom.set(pos);
      distFrom.sub(boidPos);
	  if(distFrom.length() < PROXIMITY*1.5f) {  // see further
        preyPos.add( distFrom );	 // add distance to tally 
        numClosePrey++;
      }
      i++;
    }
	if (numClosePrey > 0) {
	  preyPos.scale(1.0f/numClosePrey);  // calculate average position
      // scale to reduce distance moved towards the position
      preyPos.scale(FIND_WEIGHT);
    }
    return preyPos;
  } // end of findClosePrey()


} // end of PredatorBehavior class