/*
 * nm1.java - revised 23 Nov 07 width 526, height 231
 * @author jackord@kw.igs.net
 * string of length L, clamped at both ends
 * "Pluck" and "Pulse" initial displacements
 * motion generated by superposition of waves of wavelength 2L
 *   travelling in opposite directions
 * y(L/4) is plotted versus time
 */

import java.applet.Applet;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class nm1 extends Applet
                 implements ActionListener, Runnable {
  int kk=0; int plt=0; int first=0;                    // Declarations
  String b1s="Pluck"; Button b1=new Button(b1s);
  String b2s="Pulse"; Button b2=new Button(b2s);
  String b3s="Motion"; Button b3=new Button(b3s);
  Image bim;
  Graphics bgr;
  Thread tmr;

  public void init() {
    add(b1); add(b2); add(b3);
    b1.addActionListener(this);
    b2.addActionListener(this);
    b3.addActionListener(this);
    setBackground(new Color(211, 211, 211));
  }

  public void start() {
    if (tmr==null) {
      tmr=new Thread(this);
      tmr.setPriority(Thread.MIN_PRIORITY);
      tmr.start();
    }
  }

  public void stop() {
    tmr=null; plt=0;
  }

  public void run() {
    repaint();
  }

  public void paint(Graphics g) {
    int n=384;
    int jt, ia, ib, x1, y1, x2, y2, r, del, delt;      // Declarations
    int [] xx=new int[n+1];
    int [] yy=new int[n+1];
    int [] y=new int[2*n+1];
    g.setColor(Color.black);
    g.drawRect(0, 0, 525, 230);
    g.drawLine(393, 129, 521, 129);                    // y[L/4] plot axis
    g.setColor(Color.red);
    if (first==0) {
      bim=createImage(n+1, 200);                       // Animation buffer
      bgr=bim.getGraphics();
      first=1;
    }
    x1=0; y1=0; x2=0; y2=0; r=4;
    if (kk>0) {
      for (int i=0; i<=n; i=i+1) {
        xx[i]=i;
      }
      if (kk==1) {                                     // Init pluck
        for (int i=0; i<=n/2; i=i+1) {
          y[i]=i; y[n-i]=y[i];
        }
      }
      else {                                           // Init pulse
        for (int i=3*n/8; i<=n/2; i=i+1) {
          y[i]=4*(i-3*n/8); y[n-i]=y[i];
        }
      }
      for (int i=0; i<=n; i=i+1) {                     // Extend wave to 2L
        y[n+i]=-y[i];
      }
      long tt=System.currentTimeMillis(); del=20;
      jt=0;
      do {                                             // Main loop
        bgr.setColor(getBackground());                 // Clear plot buffer
        bgr.fillRect(0, 0, 384, 249);
        bgr.setColor(Color.black);
        bgr.drawLine(0, 80, 0, 120); bgr.drawLine(384, 80, 384, 120);
        bgr.setColor(Color.blue);
        for (int i=0; i<=n; i=i+1) {
          ia=i+jt; while (ia>2*n) { ia=ia-2*n; }       // Wave moving left
          ib=i-jt; while (ib<0) { ib=ib+2*n; }         // Wave moving right
          yy[i]=100-(y[ia]+y[ib])/4;                   // Superposition
        }
        bgr.drawPolyline(xx, yy, n);                   // Draw string
        bgr.setColor(Color.red);
        bgr.fillArc(xx[n/4]-r, yy[n/4]-r, 2*r+1, 2*r+1, 0, 360);
        x2=393+2*jt/12; y2=yy[n/4]+29;
        if (jt>0) {
          g.drawLine(x1, y1, x2, y2);                  // Plot y[L/4] vs time
        }
        x1=x2; y1=y2;
        g.drawImage(bim, 4, 29, null);                 // Show plot buffer
        if (tt>System.currentTimeMillis()) { delt=del; } else { delt=0; }
        try {
          Thread.sleep(delt);
        }
        catch (InterruptedException e) {
          stop();
        }
        tt=tt+del; jt=jt+1; if (jt==2*n+1) { kk=0; plt=0; }
      } while (plt==1);
    }
    stop();
  } 

  public void actionPerformed(ActionEvent e) {         // Buttons
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=1; start(); }
    if (b2s.equals(tst)) { kk=2; start(); }
    if (b3s.equals(tst)) { if (kk>0) { plt=1; } start(); } 
  }
}