/*
 * nm2.java - revised 25 Nov 07 - width 526, height 261
 * @author jackord@kw.igs.net
 * motion of 8-segment string clamped at both ends
 * time dependence from Newton's law
 * 'Pluck', 'Pulse', and Normal Mode initial displacements
 * y[n/4] plotted versus time for Pluck and Pulse displacements
 * dispersion relation plotted for the Normal Modes
 */

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

public class nm2 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);
  String b4s="Nmodes"; Button b4=new Button(b4s);
  Image bim;
  Graphics bgr;
  Thread tmr;

  public void init() {
    add(b1); add(b2); add(b3); add(b4); 
    b1.addActionListener(this);
    b2.addActionListener(this);
    b3.addActionListener(this);
    b4.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; 
  }

  public void run() {
    repaint();
  }

  public void wait(int del) {
    try {
      Thread.sleep(del);
    }
    catch (InterruptedException e) {
      stop();
    }
  }

  public void paint(Graphics g) {
    int n=8; int mode=0; long tt;                      // Declarations
    int [] xx=new int[n+1];
    int [] yy=new int[n+1];
    double [] y=new double[n+1];
    double [] v=new double[n+1];
    int x1, y1, x2, y2, r, jt, tst, del;          
    double t, tf, dt, pi;
    x1=0; y1=0; x2=0; y2=0; pi=Math.PI;
    g.setColor(Color.black);
    g.drawRect(0, 0, 525, 260);
    if (first==0) {
      bim=createImage(393, 230);                       // Animation buffer
      bgr=bim.getGraphics();
      first=1;
    }
    for (int i=0; i<=n; i=i+1) {
      xx[i]=4+384/n*i;
    }
    if ((kk==1)||(kk==2)) {
      g.drawLine(395, 144, 523, 144);                  // y[n/4] plot axis
      g.setColor(Color.red);
      dt=0.1*n/768;
      if (kk==1) {                                     // Init pluck
        for (int i=0; i<=n/2; i=i+1) {
          y[i]=224.*i/n; y[n-i]=y[i];
        }
      }
      if (kk==2) {                                     // Init pulse
        for (int i=3*n/8; i<=n/2; i=i+1) {
          y[i]=896.*(i-3*n/8)/n; y[n-i]=y[i];
        }
      }
      for (int i=1; i<=n-1; i=i+1) {                   // Feynman half-step
        v[i]=v[i]+(y[i-1]+y[i+1]-2*y[i])*dt/2;
      }
      jt=0; x1=395; y1=144-(int)(y[n/4]); r=4;
      tt=System.currentTimeMillis(); del=12;
      do {                                             // Main loop
        x2=395+jt/12; y2=144-(int)(y[n/4]);
        if (x2>x1) {
          g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;    // Plot y[n/4] versus t
        }
        bgr.setColor(getBackground());                 // Clear plot buffer
        bgr.fillRect(0, 0, 393, 230);
        bgr.setColor(Color.black);
        bgr.drawLine(4, 95, 4, 135); bgr.drawLine(388, 95, 388, 135);
        bgr.setColor(Color.blue);
        for (int i=0; i<=n; i=i+1) {                   // Draw blue string
          yy[i]=115-(int)(y[i]+.5);
        }
        bgr.drawPolyline(xx, yy, n+1);
        if (n<96) {
          for (int i=0; i<=n; i=i+1) {
            if (i==n/4) { bgr.setColor(Color.red); }
            bgr.fillArc(xx[i]-r, yy[i]-r, 2*r+1, 2*r+1, 0, 360);
            if (i==n/4) { bgr.setColor(Color.blue); }
          }
        }
        g.drawImage(bim, 1, 29, null);                 // Show plot buffer
        jt=jt+1;                                       // Step time
        for (int j=1; j<=10; j=j+1) {
          for (int i=1; i<=n-1; i=i+1) {               // Step y[]
            y[i]=y[i]+v[i]*dt;
          }
          for (int i=1; i<=n-1; i=i+1) {               // Step v[] (F=ma)
            v[i]=v[i]+(y[i-1]+y[i+1]-2*y[i])*dt;
          }
        }
        if (tt>System.currentTimeMillis()) { wait(del); }
        tt=tt+del; if (jt==1537) { kk=0; plt=0; }
      } while (plt==1);                                // Close main loop
    }
    if (kk==3) {
      g.drawLine(395, 144, 523, 144); g.drawLine(395, 16, 395, 144);
      g.drawLine(395, 16, 403, 16); g.drawString("0.4 Hz", 407, 21);
      g.drawString("Mode", 395+64-12, 176);
      do {                                             // Normal mode loop
        mode=mode+1; t=0; tf=10; dt=0.05/mode; tst=1; r=4;
        for (int i=0; i<=n; i=i+1) {
          y[i]=108*Math.sin(pi*mode*i/n);
        }
        for (int i=1; i<=n-1; i=i+1) {                 // Feynman half-step
          v[i]=(y[i-1]+y[i+1]-2*y[i])*dt/2;
        }
        tt=System.currentTimeMillis(); del=30;
        do {                                           // Main loop
          bgr.setColor(getBackground());               // Clear plot buffer
          bgr.fillRect(0, 0, 392, 229);
          bgr.setColor(Color.black);
          bgr.drawLine(4, 95, 4, 135); bgr.drawLine(388, 95, 388, 135);
          bgr.setColor(Color.blue);
          for (int i=0; i<=n; i=i+1) {                 // Draw blue string
            yy[i]=115-(int)(y[i]+.5);
            bgr.fillArc(xx[i]-r, yy[i]-r, 2*r+1, 2*r+1, 0, 360);
          }
          bgr.drawPolyline(xx, yy, n+1);
          g.drawImage(bim, 1, 29, null);               // Show plot buffer
          if (t==0) { wait(1000); tt=tt+1000; }
          t=t+dt;                                      // Step time
          for (int i=1; i<=n-1; i=i+1) {               // Step y[]
            y[i]=y[i]+v[i]*dt; 
          }
          for (int i=1; i<=n-1; i=i+1) {               // Step v[] (F=ma)
            v[i]=v[i]+(y[i-1]+y[i+1]-2*y[i])*dt;
          }
          if ((tst==1)&&(y[1]<0)) {
            tf=4*(t-y[1]/v[1]); tst=0;
          }
          if (tt>System.currentTimeMillis()) { wait(del); }
          tt=tt+del; 
        } while (t<tf+dt/2);
        g.setColor(Color.black);                       // Show mode number
        g.drawString(""+mode, 395+16*mode-4, 160);
        g.setColor(Color.red); r=3;                        // Plot frequency
        g.fillArc(395+16*mode-r, 144-(int)(128/.4/tf+.5)-r, 2*r+1, 2*r+1, 0, 360);
        wait(1000); 
      } while (mode<7);
      g.setColor(Color.blue); x1=395; y1=144;          // Plot dispersion reln
      for (int i=1; i<=128; i=i+1) {
        x2=x1+1; y2=144-(int)(128/.4/pi*Math.sin(i*pi/256)+.5);
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
      }
    }
    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==1)||(kk==2)) { plt=1; start(); } }
    if (b4s.equals(tst)) { kk=3; start(); }
  }
}