// 2D percolating cluster,  Evgeny Demidov  22 Oct 2001
  import java.awt.*;
  import java.awt.event.*;
  public class applet-math-cluster extends java.applet.Applet
   implements MouseListener, ItemListener, KeyListener{
    int L = 25,L1,L2, d, w, hd, hBut = 30,
      cl[], nb[], maxCl;
    double p = .5;
    Image buffImage;     Graphics buffGraphics;
    boolean painted = false;
    Choice chL;    Label  lbL, lbP;    TextField tfP;
    long generTime;
  
  public void init() {
    w = getSize().width;
    cl = new int[(w+1)*(w+2)];  nb = new int [w*w];
    String s=getParameter("L");
    if (s != null) L = Integer.parseInt(s);
    d = w/L;  hd = w-d; L1 = L+1; L2 = L+2;
    maxCl = L1*L2;
    s=getParameter("p");
    if (s != null) p = Double.valueOf(s).doubleValue();
    buffImage = createImage(w, w);   buffGraphics = buffImage.getGraphics();
    addMouseListener(this);
    chL = new Choice();
    if (w == 400)
     for (int i = 0, l = 25; i < 5; i++){
      chL.addItem(Integer.toString(l));  l *= 2;}
    else
     for (int i = 0, l = 20; i < 6; i++){
      chL.addItem(Integer.toString(l));  l *= 2;};
    chL.select(""+L);
    chL.addItemListener(this);
    lbL = new Label("L");  add(lbL);  add(chL);
    lbP = new Label("p");  add(lbP);
    tfP = new TextField( "" + (float)p, 5);  add(tfP);
    tfP.addKeyListener(this);
  }
  public void destroy() {
    removeMouseListener(this);
  }
  public void mouseClicked(MouseEvent e){}       // event handling
  public void mousePressed(MouseEvent e) {
    painted = false;
    repaint();
    e.consume();
  }
  public void mouseReleased(MouseEvent e){}
  public void mouseEntered(MouseEvent e) {}
  public void mouseExited(MouseEvent e)  {}
  public void keyTyped(KeyEvent e){}
  public void keyPressed(KeyEvent e){}
  public void keyReleased(KeyEvent e){
    final int keyEnter = 10;
    if (e.getKeyCode() == keyEnter){
      try{ p = Double.valueOf(tfP.getText()).doubleValue();
      }catch(NumberFormatException ne){}
      painted = false;
      repaint();
    }
    e.consume();
  }
  public void itemStateChanged(ItemEvent e){
    L = Integer.parseInt(chL.getSelectedItem());
    d = w/L;  hd = w-d; L1 = L+1; L2 = L+2;
    maxCl = L1*L2;
    painted = false;
    repaint();
  }
  
  public void paint(Graphics g) {
   if ( !painted ){
    generTime = System.currentTimeMillis();
    showStatus( "growing cluster");
    buffGraphics.setColor(Color.white);
    buffGraphics.fillRect(0, 0, w, w);
    for (int i = L1; i < maxCl; i++) cl[i] = 0;
    for (int i = 0; i < L1; i++) cl[i] = cl[maxCl-1-i] = -1;
    for (int i = L1; i < maxCl; i += L1) cl[i] = -1;
    int i0 = L2*(L/2+1),  delNb[] = {1,-1,L1,-L1};
  //System.out.println("=");
    cl[i0] = 1;
    for (int i = 0; i < 4; i++) nb[i] = i0 + delNb[i];
    int lastNb = 3;
    do{
     int lastCl = nb[lastNb--];
     if (cl[lastCl] == 0){
      if (Math.random() > p) cl[lastCl] = -1;
      else{
       cl[lastCl] = 1; 
       for (int i = 0; i < 4; i++){
        int k = lastCl+delNb[i];
        if (cl[k] == 0) nb[++lastNb] = k;}}}
    } while (lastNb >= 0);
  
    showStatus( "drawing");
    buffGraphics.setColor(Color.black);
    for (int i = 0; i < L; i++)
     for (int j = 0; j < L; j++)
      if ( cl[j+1+(i+1)*L1] > 0)
       buffGraphics.fillRect(j*d,hd-i*d, d,d);
    generTime = System.currentTimeMillis() - generTime;
    painted = true;}
   g.drawImage(buffImage, 0, hBut, this);
   showStatus( "p=" + (float)p + "  t=" + generTime + "ms");
  }
  
  public void update(Graphics g){ paint(g); }
  
  }