Java Tutorial/J2ME/Screen Buffer

Off screen canvas

   <source lang="java">

import javax.microedition.lcdui.Canvas; import javax.microedition.lcdui.rumand; import javax.microedition.lcdui.rumandListener; import javax.microedition.lcdui.Display; import javax.microedition.lcdui.Displayable; import javax.microedition.lcdui.Graphics; import javax.microedition.lcdui.Image; import javax.microedition.midlet.MIDlet; class OffscreenCanvas extends Canvas {

 private Image mImage;
 public void paint(Graphics g) {
   if (mImage == null)
     initialize();
   g.drawImage(mImage, 0, 0, Graphics.TOP | Graphics.LEFT);
 }
 private void initialize() {
   int w = getWidth();
   int h = getHeight();
   mImage = Image.createImage(w, h);
   Graphics g = mImage.getGraphics();
   g.drawRect(0, 0, w - 1, h - 1);
   g.drawLine(w - 1, 0, 0, h - 1);
 }

} public class OffscreenMIDlet extends MIDlet {

 public void startApp() {
   Displayable d = new OffscreenCanvas();
   d.addCommand(new Command("Exit", Command.EXIT, 0));
   d.setCommandListener(new CommandListener() {
     public void commandAction(Command c, Displayable s) {
       notifyDestroyed();
     }
   });
   Display.getDisplay(this).setCurrent(d);
 }
 public void pauseApp() {
 }
 public void destroyApp(boolean unconditional) {
 }

}</source>

Use Image as buffer

   <source lang="java">

import javax.microedition.lcdui.Canvas; import javax.microedition.lcdui.Display; import javax.microedition.lcdui.Font; import javax.microedition.lcdui.Graphics; import javax.microedition.lcdui.Image; import javax.microedition.midlet.MIDlet; public class ImageBufferGraphicsMIDlet extends MIDlet {

 private Display display;
 protected void startApp() {
   Canvas canvas = new LineCanvas();
   display = Display.getDisplay(this);
   display.setCurrent(canvas);
 }
 protected void pauseApp() {
 }
 protected void destroyApp(boolean unconditional) {
 }

} class LineCanvas extends Canvas {

 public void paint(Graphics g) {
       int width = getWidth();
       int height = getHeight();
       Image image = Image.createImage(width, height);
       Graphics imageGraphics = image.getGraphics();
       imageGraphics.fillRect(0, 0, width, height);
       int count = 10;
       int yIncrement = height/count;
       int xIncrement = width/count;
       for (int i = 0, x = xIncrement, y = 0; i < count; i++) {
           imageGraphics.setColor(0xC0 + ((128 + 10 * i) << 8) + ((128 + 10 * i) << 16));
           imageGraphics.drawLine(0, y, x, height);
           y += yIncrement;
           x += xIncrement;
       }
       imageGraphics.setFont(Font.getFont(Font.FACE_PROPORTIONAL,
                               Font.STYLE_UNDERLINED, Font.SIZE_SMALL));
       imageGraphics.setColor(0xffff00);
       imageGraphics.drawString("Image Graphics", width/2, 0, Graphics.TOP | Graphics.HCENTER);
       g.drawImage(image, 0, 0, Graphics.TOP | Graphics.LEFT);
 }

}</source>