// Helium Zee Poincare map,   Evgeny Demidov,  12 Apr 2003
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.util.StringTokenizer;
public class @file extends java.applet.Applet implements MouseListener,
  KeyListener, ActionListener{
  int w,h,w2,h2,  Mx=70, My=50, it = 5;
  double Qo=3.5, Po=2.8, dP = .2,
         Q1_1, P1_1, Q2_1, P2_1, Q12, Q22,
         Pmax = 7,  ds=.0005, ds2, ds8,t;
  Image buffImage; Graphics buffGraphics;
  boolean   bClear = true;
  Label     lbDs;
  TextField tfDs;
  Button    btClear;

public void init() {
  w = getSize().width;   h = getSize().height;
  w2 = w/2; h2 = h/2;
  buffImage = createImage(w, h);
  buffGraphics = buffImage.getGraphics();
  String s=getParameter("ds");
  if (s != null) ds = Double.valueOf(s).doubleValue();
  ds2 = ds*2; ds8 = ds/8;
  s=getParameter("dp");  if (s != null){
    StringTokenizer st = new StringTokenizer(s);
    it = Integer.parseInt(st.nextToken());
    Qo = Double.valueOf(st.nextToken()).doubleValue();
    Po = Double.valueOf(st.nextToken()).doubleValue();
    dP = Double.valueOf(st.nextToken()).doubleValue();}
  s=getParameter("mxy");  if (s != null){
    StringTokenizer st = new StringTokenizer(s);
    Mx = Integer.parseInt(st.nextToken());
    My = Integer.parseInt(st.nextToken());}

  lbDs = new Label("ds", Label.RIGHT); add(lbDs);
  tfDs = new TextField( "" + ds, 5);   add(tfDs);
  tfDs.addKeyListener(this);
  btClear = new Button("Clear"); btClear.addActionListener(this); add(btClear);
  addMouseListener(this);
  clear();
  buffGraphics.setColor(Color.black);
  for (int i = 0; i < it; i++){ 
    Po += dP;
    integrate();}
}
public void destroy(){
  removeMouseListener(this);
}

public void integrate() {
  double Q1_0, P1_0, Q2_0, P2_0, Q1_12, Q2_12, R12;
  t = 0;
  Q1_1 = Qo; P1_1 = Po;    Q2_1 = 0.; P2_1 = -4.;
  while(t < 50.){
    Q1_0 = Q1_1; Q2_0 = Q2_1;    P1_0 = P1_1; P2_0 = P2_1;
    Q12 = Q1_1*Q1_1;  Q22 = Q2_1*Q2_1;

    Q1_12 = Q1_0 + P1_0*Q22*ds8;
    Q2_12 = Q2_0 + P2_0*Q12*ds8;
    Q12 = Q1_12*Q1_12;    Q22 = Q2_12*Q2_12;  R12 = Q12 - Q22;  R12 *= R12;

    P1_1 = P1_0 + Q1_12*(2. - P2_0*P2_0/8. - Q22*(1. - Q22/R12))*ds2;
    P2_1 = P2_0 + Q2_12*(2. - P1_0*P1_0/8. - Q12*(1. + Q12/R12))*ds2;

    Q1_1 = Q1_12 + P1_1*Q22*ds8;
    Q2_1 = Q2_12 + P2_1*Q12*ds8;
    t += ds;
    if( (Math.abs(P1_1) > Pmax) || (Math.abs(P2_1) > Pmax) ) break;
    if (Q2_1*Q2_0 < 0.){
      int x  = (int)(Mx*Q1_1), y  = (int)(My*P1_1);
      buffGraphics.drawLine( x,h2-y, x,h2-y);}
  }
  repaint();
}

public void mouseClicked(MouseEvent e){}       // event handling
public void mousePressed(MouseEvent e) {
  int mx0 = e.getX(),  my0 = h2 - e.getY();
  Qo = (double)mx0/Mx;  Po = (double)my0/My;
  buffGraphics.setColor(Color.red);
  integrate();
}
public void mouseReleased(MouseEvent e){}
public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e)  {}
public void actionPerformed(ActionEvent e){
  clear(); repaint();
}
public void keyTyped(KeyEvent e) {}
public void keyPressed(KeyEvent e) {}
public void keyReleased(KeyEvent e) {
  final int keyEnter = 10;
  if (e.getKeyCode() == keyEnter) {
    try{
      ds = Double.valueOf(tfDs.getText()).doubleValue();
      ds2 = ds*2; ds8 = ds/8;
    }catch ( NumberFormatException ne) {}
  }
  e.consume();
}

public void clear(){
  buffGraphics.setColor(Color.white);
  buffGraphics.fillRect(0, 0, w, h);
  buffGraphics.setColor(Color.lightGray);
  buffGraphics.drawLine(0,0,0,h);
  buffGraphics.drawLine(0,h2,w,h2);
}

public void paint(Graphics g) {
  g.drawImage(buffImage, 0, 0, this);
  showStatus("Q=" + (float)Qo + "  P=" + (float)Po + "   s=" + (float)t );
}
public void update(Graphics g){ paint(g); }

}