Move a clipping region around a Canvas
/*-------------------------------------------------- * 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(); } }
1. | Clipping Region |