Mega Code Archive
Move a clipping region around a Canvas
<![CDATA[
/*--------------------------------------------------
* Clip.java
*
* Move a clipping region around a Canvas
*
* 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.*;
import java.util.*;
public class Clip extends MIDlet
{
private Display display; // The display
private ClipCanvas canvas; // Canvas
public Clip()
{
display = Display.getDisplay(this);
canvas = new ClipCanvas(this);
}
protected void startApp()
{
display.setCurrent( canvas );
}
protected void pauseApp()
{ }
protected void destroyApp( boolean unconditional )
{ }
public void exitMIDlet()
{
destroyApp(true);
notifyDestroyed();
}
}
/*--------------------------------------------------
* Class ClipCanvas
*
* Display the clipping region
*-------------------------------------------------*/
class ClipCanvas extends Canvas implements CommandListener
{
private Command cmExit; // Exit
private Clip midlet; // Main midlet
private Image im = null; // Image to display
private Random random; // Get random number
private int clipx = 0, clipy = 0, // View port
clipw = 45, cliph = 45; // (clipping region)
private int old_clipx = 0, old_clipy = 0; // Last clipping region
public ClipCanvas(Clip midlet)
{
this.midlet = midlet;
// Create exit command & listen for events
cmExit = new Command("Exit", Command.EXIT, 1);
addCommand(cmExit);
setCommandListener(this);
// Get random values for starting point
random = new java.util.Random();
// Make sure the entire clipping region is
// visible on the display
clipx = Math.min((getWidth() - clipw),
(random.nextInt() >>> 1) % getWidth());
clipy = Math.min((getHeight() - cliph),
(random.nextInt() >>> 1) % getHeight());
try
{
// Create immutable image
im = Image.createImage("/house.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 only the previous clipping region
g.setColor(255, 255, 255);
g.fillRect(old_clipx, old_clipy, clipw, cliph);
// Set the new clipping region
g.setClip(clipx, clipy, clipw, cliph);
// Draw image
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)
{
// Save the last clipping region
old_clipx = clipx;
old_clipy = clipy;
switch (getGameAction(keyCode))
{
case UP:
// Move clipping region up 3 pixels
if (clipy > 0)
clipy = Math.max(0, clipy - 3);
break;
case DOWN:
// Move clipping region down 3 pixels
if (clipy + cliph < getHeight())
clipy = Math.min(getHeight(), clipy + 3);
break;
case LEFT:
// Move clipping region left 3 pixels
if (clipx > 0)
clipx = Math.max(0, clipx - 3);
break;
case RIGHT:
// Move clipping region right 3 pixels
if (clipx + clipw < getWidth())
clipx = Math.min(getWidth(), clipx + 3);
break;
case FIRE:
// Show the whole screen by reseting
// the clipping region to the entire display
clipx = clipy = 0;
clipw = getWidth();
cliph = getHeight();
}
repaint();
}
}
]]>