ship.java

一个j2me的游戏的实现.需要添加一个mathfp类来支持浮点数.

import net.jscience.math.kvm.MathFP;
import javax.microedition.lcdui.*;
import java.io.IOException;

/**
 * Class to handle the drawing and movement of a little spaceship. Image is
 * loaded in a Sprite from the ship.png file. This version adds a red version
 * of the ship (the graphics for that are also in ship.png)
 * @author Martin J. Wells
 */
public class Ship extends Actor
{
   private static int SHIP_FRAME_WIDTH = 16;
   private static int SHIP_FRAME_HEIGHT = 16;
   private static final int ENEMY_IGNORE_DISTANCE = 100;
   public static final int FP_22P5 = MathFP.toFP("22.5");
   private static ImageSet playerShipImageSet;
   private static ImageSet enemyShipImageSet;

   private Sprite shipSprite;
   private long msSinceLastAIUpdate;   // The time since we last engaged the
                                       // brain
   private long msPerAIUpdate = 200;   // Delay to run the brain code; since
                                       // it's a slow thing to do we don't
                                       // want it running every cycle.
   private boolean isEnemy;

   // Weapons fire.
   private boolean firing;             // Is the ship currently firing?
   private int firingDelay=500;        // The delay between shots (in ms)
   private long timeLastFired;			// Used to track when I can fire again

   /**
    * Constructs a new ship starting at a position with a default maximum
    * velocity of 2 and thrust of 0.2.
    * @param worldArg The world this actor is in.
    * @param startX The starting x position.
    * @param startY The starting y position.
    */
   public Ship(World worldArg, boolean isEnemyArg, int startX, int startY)
   {
      super(worldArg, startX, startY, 0, 16, MathFP.toFP("2.0"), MathFP.toFP("0.2"),
            0, MathFP.toFP("-0.8"), 23);

      if (playerShipImageSet == null)
      {
         try
         {
            Image shipGraphic = Image.createImage("/ship.png");

            // Extract out the image frames for the player ship.
            Image[] playerShipFrames = ImageSet.extractFrames(shipGraphic,
                0, 0, 4, 4, SHIP_FRAME_WIDTH, SHIP_FRAME_HEIGHT);
            playerShipImageSet = new ImageSet(1);
            playerShipImageSet.addState(playerShipFrames, 0);

            // Extract out the image frames for the enemy ship. The red fighter
            // frames start 4 frames across in the file (4 * 16).
            Image[] enemyShipFrames = ImageSet.extractFrames(shipGraphic,
                4*16, 0, 4, 4, SHIP_FRAME_WIDTH, SHIP_FRAME_HEIGHT);
            enemyShipImageSet = new ImageSet(1);
            enemyShipImageSet.addState(enemyShipFrames, 0);
         }
         catch (IOException ioe)
         {
            System.out.println("unable to load image");
         }
      }

      // Set the ship sprite based on the type. If it's an enemy we use the
      // red ship frames.
      isEnemy = isEnemyArg;

      if (isEnemy)
         shipSprite = new Sprite(enemyShipImageSet, 0, 0);
      else
         shipSprite = new Sprite(playerShipImageSet, 0, 0);
   }

   /**
    * Fires a Bullet by projecting a point just beyond the front of the Ship
    * and then constructs a new Bullet facing the same direction as the Ship.
    */
   public void fire()
   {
      int[] nosePos = Actor.getProjectedPos(getX()+ (SHIP_FRAME_WIDTH/2),
                                            getY()+ (SHIP_FRAME_HEIGHT/2),
                                            getDirection(), 12);

      getWorld().addActor( new Bullet(getWorld(), nosePos[0], nosePos[1],
                                      getDirection()) );
   }

   /**
    * Cycling for the Ship calls Actor.cycle to handle movement. It then checks
    * to see if this is an enemy type ship and updates the direction based on
    * the relative angle of the player's ship from the the enemy one.
    * @param deltaMS The amount of time that has passed since the last cycle
    * (in milliseconds).
    */
   public void cycle(long deltaMS)
   {
      super.cycle(deltaMS);

      if (isEnemy)
      {
         // If insufficient time has passed to do an AI update we just add the
         // deltaMS time to the counter. If enough time has passed it executes
         // the Enemy AI code (this is only done periodically since it's
         // typically expensive stuff you don't want to do every frame).
         if (msSinceLastAIUpdate < msPerAIUpdate)
            msSinceLastAIUpdate += deltaMS;
         else
         {
            msSinceLastAIUpdate -= msPerAIUpdate; // take off one update's worth

            // Calculate the distance to the player so we ignore cases where
            // the player is too far away to bother with.
            Ship playerShip = GameScreen.getGameScreen().getPlayerShip();
            int d = distanceTo(playerShip);
            if (d < ENEMY_IGNORE_DISTANCE)
            {
               // Figure out the angle we need to face to fly directly towards
               // the player's ship.
               int facingAngle = getFacingAngle(getX(), getY(), playerShip.getX(),
                                                playerShip.getY());
               // Set this to be our target direction. The Actor.cycle method
               // will take care of turning this ship until it faces the target
               // angle we set here.
               setTargetDirection(facingAngle);
            }
         }
      }
      if (firing)
      {
         // Calculate the amount of time that has passed. If it's greater than
         // the firing delay then the Ship is clear to fire again.
         long timeSinceLastFire = (System.currentTimeMillis() - timeLastFired);
         if (timeSinceLastFire > firingDelay)
         {
            int[] nosePos = Actor.getProjectedPos(getX()+ (SHIP_FRAME_WIDTH/2),
                                                  getY()+ (SHIP_FRAME_HEIGHT/2),
                                                  getDirection(), 12);

            // Add the new bullet actor to our world.
            getWorld().addActor( new Bullet(getWorld(), nosePos[0], nosePos[1],
                                            getDirection()) );

            // Update the time the last fire took place (now).
            timeLastFired = System.currentTimeMillis();
         }
      }
   }

   public final void setFiring(boolean b)
   {
      firing = b;
   }

   /**
    * Actor render method to draw the ship. In this code we set the frame
    * corresponding to the direction the ship is facing. Note that the
    * shipSprite is either a red or yellow ship based on the type specified
    * in the constructor.
    * @param graphics The graphics context upon which to draw the sprite frame.
    * @param offsetX The amount to offset the x drawing position by.
    * @param offsetY The amount to offset the y drawing position by.
    */
   public void render(Graphics graphics, int offsetX, int offsetY)
   {
      int frame = MathFP.toInt(MathFP.div(MathFP.toFP(getDirection()),
                                          FP_22P5));

      shipSprite.setFrame(frame);
      shipSprite.draw(graphics, getX()-offsetX, getY()-offsetY);
   }

   public int getHeight()
   {
      return SHIP_FRAME_HEIGHT;
   }

   public int getWidth()
   {
      return SHIP_FRAME_WIDTH;
   }

   /**
    * @return The x position of the center of the ship
    */
   public int getCenterX()
   {
      return getX() + getWidth() / 2;
   }

   /**
    * @return The y position of the center of the ship
    */
   public int getCenterY()
   {
      return getY() + getHeight() / 2;
   }
}