import java.awt.*;

/**
    Program:  NoisyWave24
    Purpose:  
    @author:  Paul Garrett, garrett@math.umn.edu
    @version: 24, Fri Jan 17 15:40:28 CST 1997
*/

public class NoisyWave24 extends java.applet.Applet implements Runnable {

  Thread theThread;
  int[][] thePoints; // time, enumerate points, y
  int theTime; //
  int numberSubintervals; // 
  int totalTime; // total number of frames
  float theSpeed; // default = 1
  int xIncrement; // increment in x

  int waveConstant;

  boolean queryInit; // to tell whether computations done and ready...

  Color bgColor; // background
  Color fgColor; // foreground

  Image offScreenImage; // for double-buffering
  Graphics offScreenGraphics; // ditto

  /* Above are all the instance variables.... */

  public void init() {

    waveConstant = 2;

    offScreenImage = createImage(this.size().width,
				 this.size().height); // size of applet
    offScreenGraphics = offScreenImage.getGraphics();

    //Button go = new Button("go");
    //add(go);
    //Button stop = new Button("stop");
    //add(stop);

    bgColor = Color.darkGray;
    fgColor = Color.white; // for example...... reverse video...
    setBackground(bgColor);
    setForeground(fgColor);
    //    offScreenGraphics.setBackground(bgColor); // does this work? NO?!
       
   
    numberSubintervals = 100;
    xIncrement = 4; // screen width vs. numberS * xInc and 420...

    theTime = 0;
    totalTime = 400;
    
    computeFrames();
  }

  void computeFrames() {
    thePoints = new int[totalTime][numberSubintervals + 1]; // NB the "+1"

    thePoints[0][0] = thePoints[1][0] = 0; 
    thePoints[0][numberSubintervals] = thePoints[1][numberSubintervals] = 0; // endpoints fixed
      
    for (int x=0; x <= numberSubintervals / 5 ; x++) { // "5" ?
      thePoints[0][x] = thePoints[1][x] = (int) (100 * 
						 Math.sin( ((float) x) * Math.PI / 20) * 
						 Math.sin( ((float) x) * Math.PI / 20));
    } // NB other points initialized to 0 by declaration above

    for (int t=2; t<totalTime; t++) {
      thePoints[t][0] = thePoints[t][numberSubintervals] = 0; // endpoints fixed
      for (int x=1; x < numberSubintervals; x++) { // interior points
	thePoints[t][x] = ( thePoints[t-1][x-1]
	 - 2 * thePoints[t-1][x] + thePoints[t-1][x+1] ) / waveConstant
	 - thePoints[t-2][x] + 2 * thePoints[t-1][x];
      }
    }
  }
  
  public void start() {
    if (theThread == null) {
	theThread = new Thread(this);
	    theThread.start();
	}
    }
    public void stop() {
	if (theThread != null) {
	    theThread.stop();
	    theThread = null;
	}
    }

  void pause(int time) { // in milliseconds
	try { Thread.sleep(time); }
	catch ( InterruptedException e) { }
    }

    public void run() { // this calls "update" ...
	while (true) {
	  repaint();
	  theTime = (theTime + 1) % totalTime;
	  pause(100); 
	}
    }	

    public void update(Graphics g) { // don't clear the screen for duhbuff
	paint(g); 
    }

    public void paint(Graphics g) {
	
      int previousTime;
      previousTime = (theTime + totalTime -1) % totalTime;

      offScreenGraphics.setColor(bgColor);
      offScreenGraphics.fillRect(0, 0, this.size().width,
				 this.size().height);

      offScreenGraphics.setColor(fgColor);
      offScreenGraphics.drawString("Time now is " + theTime, 10, 20); // for duhbuff
      for (int x = 0; x < numberSubintervals; x++) {
	  offScreenGraphics.drawLine(50 + x * xIncrement, 150 - thePoints[theTime][x], 
		   50 + (x+1) * xIncrement, 150 - thePoints[theTime][x+1]);
      }
      g.drawImage(offScreenImage, 0, 0, this); // from offScreen
    }

} // the end