/*
 * Double-buffered version of mRectApplet.java
 */

import java.applet.*;
import java.awt.*;

public class mObjApplet extends Applet implements Runnable {

  // Instance variables:
  int numObj = 3;     // number of objects
  mPoint object[];    // object array
  Thread thread;      // a thread
  Image image;        // for double buffering
    
  // Class method:
  public void initObjects() {
    /* initialize object array */
    object = new mPoint[numObj];
    /* initialize a rectangle */
    object[0] = new mRectangle(10, 10, 100, 100);
    object[0].setDelta(1, 1);
    object[0].setColor(Color.red);
    /* initialize a circle */
    object[1] = new mCircle(200, 10, 100, 100);
    object[1].setDelta(-1, 1);
    object[1].setColor(Color.blue);
    /* initialize a triangle */
    object[2] = new mTriangle(10, 200, 100, 100);
    object[2].setDelta(-1, 1);
    object[2].setColor(Color.green);
    image = createImage(size().width, size().height);
  }

  // Override java.applet.Applet.init:
  public void init () {
    initObjects();
  }

  // Override java.applet.Applet.start:
  public void start() {
    if (thread == null) {
      // Reinitialize:
      initObjects();
      thread = new Thread(this);
      thread.start();
    }
  }
  
  // Override java.applet.Applet.stop:
  public void stop() {
    if (thread != null) {
      thread.stop();
      thread = null;
    }
  }
  
  // Implement java.lang.Runnable.run:
  public void run() {
    while(thread != null) {
      // repaint() invokes update():
      repaint();
      try {
        Thread.sleep(20);
      } 
      catch(InterruptedException e) {
        // Do nothing   
      };
    }
  }

  // Override java.awt.Component.update:
  public void update(Graphics g) {
    /* Get Off Screen Graphics Context */
    Graphics og = image.getGraphics(); 
    /* fill background */
    og.setColor(getBackground());
    og.fillRect(1, 1, size().width-2, size().height-2);
    /* draw boundry */
    og.setColor(getForeground());
    og.drawRect(0, 0, size().width-1, size().height-1);
    /* move object */
    for (int i=0; i<numObj; i++) {
      object[i].checkBoundary(bounds());
      object[i].move(og);
    }
    /* user who call getGraphics should call dispose */
    og.dispose();
    g.drawImage(image, 0, 0, this);
  }
  
  // Override java.awt.Component.paint:
  public void paint(Graphics g) {
    update(g);
  }
  
}