gamescreen.java

《J2ME Game Programming》随书光盘源代码

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Graphics;
import java.util.Vector;

public class GameScreen extends Canvas
{
   private Vector actors;
   private Ship playerShip;
   private static GameScreen theGameScreen;   // the one and only

   public GameScreen()
   {
      theGameScreen = this;

      // This code now uses a Vector instead of an array.
      actors = new Vector();

      playerShip = new Ship(false, 64, 64);
      actors.addElement(playerShip);

      // Now construct an enemy fighter.
      actors.addElement(new Ship(true, 30, 30));
   }

   /**
    * @return The player's Ship object.
    */
   public Ship getPlayerShip()
   {
      return playerShip;
   }

   /**
    * A static method to return the one and only instance of the GameScreen
    * object.
    */
   public final static GameScreen getGameScreen()
   {
      return theGameScreen;
   }

   /**
    * Canvas paint method used to draw all the Actors on the screen.
    * @param graphics The graphics context upon which to draw the Actors.
    */
   protected void paint(Graphics graphics)
   {
      graphics.setColor(0);
      graphics.fillRect(0, 0, getWidth(), getHeight());

      for (int i = 0; i < actors.size(); i++)
         ((Actor)actors.elementAt(i)).render(graphics);
   }

   /**
    * Cycle all the Actors using fixed timing of 100 milliseconds.
    */
   public void cycle()
   {
      for (int i = 0; i < actors.size(); i++)
         ((Actor) actors.elementAt(i)).cycle(100);
   }

   /**
    * Check whether the passed in Actor collides with any other Actor in the
    * GameScreen.
    * @param actorToCheck The Actor to check collisions against.
    * @return True if actorToCheck is in a collision state.
    */
   public boolean checkCollision(Actor actorToCheck)
   {
      if (actorToCheck instanceof Bullet) return false;

      // did this ship hit another?
      for (int j = 0; j < actors.size(); j++)
      {
         Actor another = (Actor)actors.elementAt(j);
         if (another != actorToCheck && !(another instanceof Bullet) &&
             Tools.isIntersectingRect(actorToCheck.getX(),
                                      actorToCheck.getY(),
                                      actorToCheck.getWidth(),
                                      actorToCheck.getHeight(),
                                      another.getX(), another.getY(),
                                      another.getWidth(),
                                      another.getHeight()))
            return true;
      }
      return false;
   }

   /**
    * Removes an Actor from the GameScreen.
    * @param a The Actor to remove.
    */
   public void removeActor(Actor a)
   {
      actors.removeElement(a);
   }

   /**
    * Adds an Actor to the GameScreen.
    * @param a The Actor to add.
    */
   public void addActor(Actor a)
   {
      actors.addElement(a);
   }

   /**
    * React to keys pressed by the user.
    * @param keyCode The code of the key the players pressed.
    */
   protected void keyPressed(int keyCode)
   {
      int action = getGameAction(keyCode);

      if (action == RIGHT)
         playerShip.setNegPeakSpin();
      if (action == LEFT)
         playerShip.setPeakSpin();
      if (action == UP)
         playerShip.setFiring(true);
   }

   /**
    * React to key being released. For this example the code stops the spin.
    * @param keyCode The code for the key that was released.
    */
   protected void keyReleased(int keyCode)
   {
		int action = getGameAction(keyCode);
		if (action == RIGHT)
			playerShip.setSpin(0);
		if (action == LEFT)
			playerShip.setSpin(0);
      if (action == UP)
         playerShip.setFiring(false);
   }
}