aliensprite.java

Reilly Killer Game Programming in Java书的源代码

// AlienSprite.java
// Andrew Davison, April 2005, [e-mail]

/* We assume the alien is facing in the +z-axis direction
   and is originally at (0, ??, 0). Rotations are specified
   relative to the original orientation along the z-axis.

   Its behaviour is
   specified in headTowardsTourist() which is called by
   update(), which is called by a TimeBehaviour object
   every few 100ms.

   Similar to the behaviour used AlienQuadSprite in Code/Tiles/
*/

import java.text.DecimalFormat;
import javax.vecmath.*;


public class AlienSprite extends TourSprite
{
  private static final double CLOSE_DIST = 0.2;

  private TourSprite ts;
  private double currAngle;   // current y-axis angle of sprite
  private DecimalFormat df;   // for simpler output during debugging


  public AlienSprite(String fnm, Obstacles obs, TourSprite ts)
  { 
    super(fnm, obs);
    df = new DecimalFormat("0.###");  // 3 dp
    this.ts = ts;
    currAngle = 0.0;
  }  // end of AlienSprite()


  public void update()
  // called by TimeBehaviour to update the alien
  {
    if (isActive()) {
      headTowardsTourist();
      if (closeTogether(getCurrLoc(), ts.getCurrLoc()))
        System.out.println("Alien and Tourist are close together");
    }
  }  // end of updateSprite()


  private void headTowardsTourist()
  /* Turn to face tourist then move towards him, unless
     there is an obstacle, then try to move round it.

     rotAngle is the angle from the original orientation 
     facing along the +z-axis. We use angleChg to move
     the alien which is the difference from the current angle
     of the alien.
  */
  { 
    double rotAngle = calcTurn( getCurrLoc(), ts.getCurrLoc());
    double angleChg = rotAngle - currAngle;
    // System.out.println("angleChg: " + df.format(angleChg));
    doRotateY(angleChg);
    currAngle = rotAngle;  // store new angle for next time

    // move forward if possible, or left, right, or back
    // this fixed ordering can lead the alien into livelock
    // if the obstacles are positioned carefully :(
    if (moveForward())
      ;
    else if (moveLeft())
      ;
    else if (moveRight())
      ;
    else if (moveBackward())
      ;
    else
      System.out.println("Alien stuck!");

  }  // end of headTowardsTourist()

				

  private double calcTurn(Point3d alienLoc, Point3d touristLoc)
  /* Calculate the angle to turn the alien around the
     y-axis, so that it is facing towards the tourist.
     This angle is relative to the original orientation
     facing along +z-axis
  */
  {  // printTuple(alienLoc, "alienLoc");
     // printTuple(touristLoc, "touristLoc");
     double zDiff = touristLoc.z - alienLoc.z;
     double xDiff = touristLoc.x - alienLoc.x;
     //System.out.println("xDiff: " + df.format(xDiff) + 
     //                    "; zDiff: " + df.format(zDiff) );

     double turnAngle = 0.0;   // the angle to rotate the alien
     if (zDiff != 0.0) {
       double angle = Math.atan( xDiff/zDiff);
       // the angle from alienLoc to touristLoc
       // System.out.println("angle: " + df.format(angle));
       if ((xDiff > 0) && (zDiff > 0))    // some redundancy for clarity
         turnAngle = angle;
       else if ((xDiff > 0) && (zDiff < 0))
         turnAngle = Math.PI + angle;    // since angle has neg value 
       else if ((xDiff < 0) && (zDiff < 0))
         turnAngle = Math.PI + angle;
       else if ((xDiff < 0) && (zDiff > 0))
         turnAngle = angle;    // since angle has neg value
     }
     else {    // zDiff == 0.0, which is unlikely with doubles
       if (xDiff > 0)
         turnAngle = Math.PI/2;
       else if (xDiff < 0)
         turnAngle = -Math.PI/2;
       else    // alien and sprite at *exact* same place
          turnAngle = 0.0;
     }
     // System.out.println("turnAngle: " + df.format(turnAngle));
     return turnAngle;
  } // end of calcAngle()


  private boolean closeTogether(Point3d alienLoc, Point3d touristLoc)
  // Are the alien and Tourist close together?
  {
    double distApart = alienLoc.distance( touristLoc );
    if (distApart < CLOSE_DIST)
      return true;
    return false;
  }  // end of closeTogether()

}  // end of AlienSprite