Off screen canvas : Screen Buffer « J2ME « Java Tutorial

1. Java Tutorial
2. J2ME
3. Screen Buffer

import javax.microedition.lcdui.Canvas;
import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
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) {
  }
}

31.34.Screen Buffer
	31.34.1.	Off screen canvas
	31.34.2.	Use Image as buffer