spritetest.java

《J2ME Game Programming》随书光盘源代码

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.io.IOException;

/**
 * A example that demonstrates the use of the ImageSet class to create a sprite.
 * Note that this is used as a precursor to creating a Sprite class, not as an
 * example of how to use the Sprite class.
 * @author Martin J. Wells
 */
public class SpriteTest extends MIDlet implements CommandListener, Runnable
{
   private static int SHIP_FRAME_WIDTH = 16;
   private static int SHIP_FRAME_HEIGHT = 16;

   private MyCanvas myCanvas;
   private Command quit;
   private Image[] shipFrames;
   private boolean running;
   private int currentFrame;

   /**
    * A custom canvas that will draw the current frame in the animation.
    */
   class MyCanvas extends Canvas
   {
      /**
       * The overidden Canvas class paint method takes care of drawing the
       * current frame.
       * @param graphics The graphics context on which you draw.
       */
      protected void paint(Graphics graphics)
      {
         graphics.setColor(0);
         graphics.fillRect(0, 0, getWidth(), getHeight());

         graphics.drawImage(shipFrames[currentFrame], getWidth() / 2,
                            getHeight() / 2,
                            Graphics.HCENTER | Graphics.VCENTER);

      }
   }

   /**
    * Constructor loads the ship.png file (make sure this image file is in the
    * JAR (and not in a subdirectory) for this code to work. After loading the
    * image we extract the frames, create an image set then setup the canvas.
    */
   public SpriteTest()
   {
      try
      {
         // Construct the image and extract the red ship frames
         Image shipImage = Image.createImage("/ship.png");
         shipFrames = ImageSet.extractFrames(shipImage, 4 * SHIP_FRAME_WIDTH,
                                             0, 4, 4, SHIP_FRAME_WIDTH,
                                             SHIP_FRAME_HEIGHT);
      }
      catch (IOException ioe)
      {
         System.out.println("unable to load image");
      }

      // Construct a the canvas
      myCanvas = new MyCanvas();

      // And a way to quit
      quit = new Command("Quit", Command.EXIT, 2);
      myCanvas.addCommand(quit);

      myCanvas.setCommandListener(this);

      // create the thread that will carry out the animation.
      running = true;
      Thread t = new Thread(this);
      t.start();
   }

   public void run()
   {
      while (running)
      {
         // Increment the current frame. Note that this is not a particular
         // good way to do animation. See the Sprite class for how to handle it
         // properly (using timing).
         currentFrame++;
         if (currentFrame > 15)
            currentFrame = 0;

         // Request a canvas repaint.
         myCanvas.repaint();
         try
         {
            // Hang around a bit.
            Thread.sleep(100);
         }
         catch (InterruptedException e)
         {
         }

      }
   }

   /**
    * Handles Application Manager notification the MIDlet is starting (or
    * resuning from a pause). In this case we set the canvas as the current
    * display screen.
    * @throws MIDletStateChangeException
    */
   protected void startApp() throws MIDletStateChangeException
   {
      Display.getDisplay(this).setCurrent(myCanvas);
   }

   /**
    * Handles Application Manager notification the MIDlet is about to be paused.
    * We don't bother doing anything for this case.
    */
   protected void pauseApp()
   {
   }

   /**
    * Handles Application Manager notification the MIDlet is about to be
    * destroyed. We don't bother doing anything for this case.
    */
   protected void destroyApp(boolean unconditional)
           throws MIDletStateChangeException
   {
   }

   /**
    * The CommandListener interface method called when the user executes
    * a Command, in this case it can only be the quit command we created in the
    * consutructor and added to the Canvas.
    * @param command The command that was executed.
    * @param displayable The displayable that command was embedded within.
    */
   public void commandAction(Command command, Displayable displayable)
   {
      try
      {
         if (command == quit)
         {
            running = false;
            destroyApp(true);
            notifyDestroyed();
         }
      }

      catch (MIDletStateChangeException me)
      {
         System.out.println(me + " caught.");
      }
   }

}