/*
 * ftjn.java - revised 17 Apr 05 - width 401, height 301
 * @author jackord@kw.igs.net
 * restricted 3-body problem:
 *   (1) locating equilibrium sites in the rotating frame using a color
 *       plot of effective potential
 *   (2) testing the stability of orbits at the Trojan and saddle point sites
 */

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

public class ftjn extends Applet 
                    implements ActionListener, Runnable {
  int kk=0; int first=0;                               // Declarations
  int x0, y0, imax;                                    // Global
  double x1, x2, m1, m2, w, w2, dt;                    //   variables
  String bs = "Plot"; Button bb = new Button(bs);
  Color col[]={ Color.blue, Color.cyan, Color.red, Color.yellow, Color.green, Color.magenta };
  Choice ch=new Choice();
  CheckboxGroup chg=new CheckboxGroup();
  Checkbox[] chb=new Checkbox[2];
  Thread tmr;

  public void init() {                                 
    setLayout(new FlowLayout(FlowLayout.LEFT));
    setBackground(new Color(211, 211, 211));
    ch.addItem("M/m=9"); ch.addItem("M/m=19");
    ch.addItem("M/m=29"); ch.addItem("M/m=99");
    ch.addItem("Jupiter"); ch.addItem("Earth");
    add(ch); add(bb);
    add(chb[0]=new Checkbox("Trojan", chg, true));
    add(chb[1]=new Checkbox("Saddle", chg, false));
    bb.addActionListener(this);
    ch.setBackground(getBackground());
    chb[0].setBackground(getBackground());
    chb[1].setBackground(getBackground());
  }

  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 pause(int n) {
    try {
      Thread.sleep(n);
    }
    catch (InterruptedException e) {
      stop();
    }
  }

  double f(double x) {                                 // Force
    double r13, r23;
    r13=Math.pow((x-x1)*(x-x1), 1.5); r23=Math.pow((x-x2)*(x-x2), 1.5);
    return w2*(x-x0)+m1*(x1-x)/r13+m2*(x2-x)/r23;
  }

  public void orbit(double x, double y, Graphics g) {  // Plot orbit
    double r13, r23, vx, vy, dvx, dvy;
    int xa, ya, xb, yb;
    r13=Math.pow((x-x1)*(x-x1)+(y-y0)*(y-y0), 1.5);
    r23=Math.pow((x-x2)*(x-x2)+(y-y0)*(y-y0), 1.5);
    dvx=(w2*(x-x0)-m1*(x-x1)/r13-m2*(x-x2)/r23)*dt;
    dvy=(w2*(y-y0)-m1*(y-y0)/r13-m2*(y-y0)/r23)*dt;
    vx=dvx/2; vy=dvy/2;
    xa=(int)(x); ya=(int)(y);
    for (int i=1; i<=imax; i=i+1) {                    // Feynman loop
      x=x+vx*dt; y=y+vy*dt;
      xb=(int)(x); yb=(int)(y);
      g.drawLine(xa, ya, xb, yb); xa=xb; ya=yb;        // Plot
      r13=Math.pow((x-x1)*(x-x1)+(y-y0)*(y-y0), 1.5);
      r23=Math.pow((x-x2)*(x-x2)+(y-y0)*(y-y0), 1.5);
      dvx=(w2*(x-x0)-2*w*(vy+dvy/2)-m1*(x-x1)/r13-m2*(x-x2)/r23)*dt;
      dvy=(w2*(y-y0)+2*w*(vx+dvx/2)-m1*(y-y0)/r13-m2*(y-y0)/r23)*dt;
      vx=vx+dvx; vy=vy+dvy;
      if ((r13<2197)||(r23<729)) { i=imax; }           // Crash
    }
  }  

  public void paint(Graphics g) {                      // Main Program
    if (first==0) {                                    // Screen layout
      bb.setBounds(5, 277, 40, 20);
      chb[0].setBounds(50, 277, 60, 20);
      chb[1].setBounds(115, 277, 60, 20);
      first=1;
    }
    double r1, r2, r13, r23, rr, d, e, f, h, u, x, y, xx, yy;
    int ii, xa, xb, ya, yb, jm, xm;
    double[] m=new double[6];
    double[] c=new double[6];
    double[] a=new double[3];
    double[] b=new double[3];
    m[0]=.1; m[1]=.05; m[2]=1./30.; 
    m[3]=.01; m[4]=.001; m[5]=.000003;
    c[0]=.209; c[1]=.2116; c[2]=.2123; 
    c[3]=.2137; c[4]=.21427; c[5]=.21429;
    x0=200; y0=150; d=140; w2=1/(d*d*d); w=Math.sqrt(w2);
    ii=ch.getSelectedIndex();
    m2=m[ii]; m1=1-m2; x1=x0-m2*d; x2=x0+m1*d;         // Site M and m
    a[0]=0; b[0]=x1-13; a[1]=x0; b[1]=x2-9; a[2]=x2+9; b[2]=400;
    xx=x1+d/2; yy=y0-d*Math.sqrt(3)/2;                 // Site Trojans
    g.setColor(Color.black);                           // Initial screen
    g.drawRect(0, 0, 400, 300);
    g.setColor(Color.gray);
    g.fillArc((int)(x1+.5)-13, y0-13, 27, 27, 0, 360);
    g.fillArc((int)(x2+.5)-9, y0-9, 19, 19, 0, 360);
    g.setColor(Color.black);
    g.drawArc((int)(x1+.5)-13, y0-13, 26, 26, 0, 360);
    g.drawArc((int)(x2+.5)-9, y0-9, 18, 18, 0, 360);
    if (kk>0) {                                        
      long tt=System.currentTimeMillis(); int del=8;
      for (int i=1; i<=399; i=i+1) {                   // Scan the screen
        for (int j=1; j<=299; j=j+1) {
          rr=(i-x0)*(i-x0)+(j-y0)*(j-y0);
          r1=Math.sqrt((i-x1)*(i-x1)+(j-y0)*(j-y0));
          r2=Math.sqrt((i-x2)*(i-x2)+(j-y0)*(j-y0));
          if ((r1>13)&&(r2>9)) {
            u=w2*rr/2+m1/r1+m2/r2;                     // Effective potential
            g.setColor(col[(int)(c[ii]/u)%6]);
            g.drawLine(i, j, i, j);                    // Color pixel
          }
        }
        if ((tt+i*del)>System.currentTimeMillis()) {
          pause(10);
        }
      }
      g.setColor(Color.black);
      g.drawArc((int)(x1+.5)-13, y0-13, 26, 26, 0, 360);
      g.drawArc((int)(x2+.5)-9, y0-9, 18, 18, 0, 360);
      if (chb[0].getState()==true) {                   // Trojan site
        g.setColor(Color.white);
        g.drawLine((int)(x1), (int)(y0), (int)(x2), (int)(y0));
        g.drawLine((int)(x1), (int)(y0), (int)(xx), (int)(yy));
        g.drawLine((int)(x2), (int)(y0), (int)(xx), (int)(yy));
        g.setColor(Color.black);
        pause(1500);
        dt=5;
        imax=(int)(32*Math.PI/w/dt); if(ii==5) { imax=10*imax; }
        x=xx; y=yy-d/400;
        orbit(x, y, g);
      }
      else {                                           // Saddle points
        g.setColor(Color.white);
        g.drawLine(0, 150, 400, 150);
        xa=0; ya=0;
        dt=1; imax=(int)(8*Math.PI/w/dt); xm=400; jm=2;
        if (ii>3) {
          xm=180; jm=0; dt=5; imax=10*imax;
          if (ii==5) { dt=50; }
        }
        for (int i=0; i<=xm; i=i+1) {
          r13=Math.pow((i-x1)*(i-x1), 1.5); r23=Math.pow((i-x2)*(i-x2), 1.5);
          xb=i; yb=(int)(150.5+2E5*(w2*(x0-i)+m1*(i-x1)/r13+m2*(i-x2)/r23));
          if ((i>0)&&(ya>0)&&(yb<300)) {
            g.drawLine(xa, ya, xb, yb);                // Plot force
          }
          xa=xb; ya=yb;     
        }
        g.setColor(Color.black);
        for (int j=0; j<=jm; j=j+1) {                  // Three saddle points
          e=a[j]; f=b[j];                              //   if ii<4
          while ((f-e)>.001) {                         // Bisection algorithm
            h=(e+f)/2;
            if (f(h)<0) { e=h; } else { f=h; }
          }
          x=(e+f)/2; y=y0-d/400;
          orbit(x, y, g);
        }
      }
    }
    kk=0; stop();
  }

  public void actionPerformed(ActionEvent e) {         // Button
    String tst;
    tst=e.getActionCommand();
    if (bs.equals(tst)) { kk=1; }
    start();
  }
}