Source Code : Translate coordinate system

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Translate coordinate system

/*--------------------------------------------------
* Translate.java
*
* Translate coordinate system
*
* Example from the book:     Core J2ME Technology
* Copyright John W. Muchow   http://www.CoreJ2ME.com
* You may use/modify for any non-commercial purpose
*-------------------------------------------------*/  
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class Translate extends MIDlet
{
  private Display  display;     // The display
  private TranslateCanvas canvas;   // Canvas 
 
  public Translate()
  {
    display = Display.getDisplay(this);
    canvas  = new TranslateCanvas(this);
  }
 
  protected void startApp()
  {
    display.setCurrent( canvas );
  }
 
  protected void pauseApp()
  { }

  protected void destroyApp( boolean unconditional )
  { }
 
  public void exitMIDlet()
  {
    destroyApp(true);
    notifyDestroyed();
  }
}

/*--------------------------------------------------
* Class Translate
*
* Draw image using translated coordinates
*-------------------------------------------------*/
class TranslateCanvas extends Canvas implements CommandListener
{
  private Command cmExit;  // Exit midlet
  private Translate midlet;
  private Image im = null;
  private int translatex = 0, translatey = 0;
 
  public TranslateCanvas(Translate midlet)
  {
    this.midlet = midlet;
    
    // Create exit command & listen for events
    cmExit = new Command("Exit", Command.EXIT, 1);
    addCommand(cmExit);
    setCommandListener(this);

    try
    {
      // Create immutable image
      im = Image.createImage("/bolt.png");
    }
    catch (java.io.IOException e)
    {
      System.err.println("Unable to locate or read .png file");
    }    
  } 

  protected void paint(Graphics g)
  {
    if (im != null)
    {
      // Clear the background
      g.setColor(255, 255, 255);
      g.fillRect(0, 0, getWidth(), getHeight());
      
      // Translate coordinates
      g.translate(translatex, translatey);      
    
      // Always draw at 0,0
      g.drawImage(im, 0, 0, Graphics.LEFT | Graphics.TOP);
    }
  }

  public void commandAction(Command c, Displayable d)
  {
    if (c == cmExit)
      midlet.exitMIDlet();
  }
  
  protected void keyPressed(int keyCode)
  {
    switch (getGameAction(keyCode))
    {
      case UP: 
      
        // If scrolling off the top, roll around to bottom
        if (translatey - im.getHeight() < 0)
          translatey = getHeight() - im.getHeight();
        else
          translatey -= im.getHeight();          
        break;
      
      case DOWN:

        // If scrolling off the bottom, roll around to top
        if ((translatey + im.getHeight() + im.getHeight()) > getHeight())
          translatey = 0;
        else
          translatey += im.getHeight();          
        break;
        
      case LEFT:
      
        // If scrolling off the left, bring around to right
        if (translatex - im.getWidth() < 0)
          translatex = getWidth() - im.getWidth();
        else
          translatex -= im.getWidth();          
        break;

      case RIGHT:
      
        // If scrolling off the right, bring around to left
        if ((translatex + im.getWidth() + translatex) > getWidth())
          translatex = 0;
        else
          translatex += im.getWidth();          
        break;
    }        
    repaint();
  }
}

           
       

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