/*
 * nm4.java - revised 28 Mar 07 - width 526, height 261
 * @author jack@ord.ca
 * n-segment string clamped at both ends for n=8, 48, 96, 192, and 384
 * time dependence from FFSS or directly from Newton's law
 * 'Pluck' and 'Pulse' initial displacements
 * y[n/4] plotted versus time
 */

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

public class nm4 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);
  Choice ch=new Choice();
  Checkbox ch1=new Checkbox("FFSS");
  Image bim;
  Graphics bgr;
  Thread tmr;

  public void init() {
    setBackground(new Color(211, 211, 211));
    ch.setBackground(getBackground());
    ch1.setBackground(getBackground());
    ch.addItem("n=8"); ch.addItem("n= 48"); ch.addItem("n= 96");
    ch.addItem("n=192"); ch.addItem("n=384");
    add(b1); add(b2); add(b3); add(ch); add(ch1);
    b1.addActionListener(this);
    b2.addActionListener(this);
    b3.addActionListener(this);
  }

  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, x1, y1, x2, y2, r, jt, del, delt;           // Declarations
    int [] nn=new int[5];
    nn[0]=8; nn[1]=48; nn[2]=96; nn[3]=192; nn[4]=384;
    n=nn[ch.getSelectedIndex()];
    int [] xx=new int[n+1];
    int [] yy=new int[n+1];
    double [] y=new double[n+1];
    double [] v=new double[n+1];
    double [] b=new double[n+1];
    double [] w=new double[n+1];
    double dt, pi;
    g.setColor(Color.black);
    g.drawRect(0, 0, 525, 260);
    g.drawLine(395, 144, 523, 144);                    // y[n/4] plot axis
    g.setColor(Color.red);
    dt=n/384.; pi=Math.PI;
    if (first==0) {
      bim=createImage(393, 230);                       // Animation buffer
      bgr=bim.getGraphics();
      first=1;
    }
    if (kk>0) {
      for (int i=0; i<=n; i=i+1) {
        xx[i]=4+384/n*i;
      }
      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];
        }
      }
      if (ch1.getState()==true) {
        for (int i=1; i<=n-1; i=i+2) {
          w[i]=2*Math.sin(pi*i/2/n);                   // Mode frequencies
          for (int j=1; j<=n-1; j=j+1) {               // FFSS coefficients
            b[i]=b[i]+2*y[j]*Math.sin(pi*i*j/n)/n;
          }
        }
      }
      else {
        dt=dt/20;
        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]+.5); r=3;
      long tt=System.currentTimeMillis(); del=12;
      do {                                             // Main loop
        x2=395+(int)(jt*128/768); y2=144-(int)(y[n/4]+.5);
        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
        if (ch1.getState()==true) {                    // Series
          for (int i=1; i<=n/2; i=i+1) {               
            y[i]=0;
            for (int k=1; k<=n-1; k=k+2) {
              y[i]=y[i]+b[k]*Math.sin(pi*i*k/n)*Math.cos(w[k]*jt*dt);
            }
            y[n-i]=y[i];
          }
        }
        else {                                         // F = Ma
          for (int j=1; j<=20; 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()) { delt=del; } else { delt=0; }
        try {
          Thread.sleep(delt);
        }
        catch (InterruptedException e) {
          stop();
        }
        tt=tt+del; if (jt==769) { kk=0; plt=0; }
      } while (plt==1);                                // Close main loop
    }
    stop();
  } 

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