// Continuum percolation,  Evgeny Demidov, 17 Feb 2002
  import java.awt.*;
  import java.awt.event.*;
  import java.awt.image.*;
  public class applet-math-contour extends java.applet.Applet
   implements ItemListener, ActionListener, MouseMotionListener{
    int  Rc = 8, Lc, w, h, lbSize = 30, iV[], maxColor = 9,
     cWhite = maxColor, cBlack = maxColor+1, hBar, hCol, nb[], delNb[];
    double V[], f[][], G[][],  Vo, sV, Vp = -.95;
    Choice chRc;    Label lbRc;    Button btNew;
    Image img, imBar;      IndexColorModel iColor;
    long generTime;
    boolean bBurn = false;
    Checkbox  cbBurn;
  
  public void init() {
    w = getSize().width - 30;
    h = getSize().height - lbSize;
    nb = new int[w*h];   delNb = new int[4];
    delNb[0] = 1; delNb[1] = -1; delNb[2] = w; delNb[3] = -w;
    String s=getParameter("Rc"); if (s != null) Rc = Integer.parseInt(s);
    s=getParameter("Vp"); if (s != null) Vp = Double.valueOf(s).doubleValue();
    V = new double[w*h];  iV = new int[w*(h+2)];
    f = new double[h+64][w+64];
    for (int i = 0; i < h+64; i++)
     for (int j = 0; j < w+64; j++) f[i][j] = 2*Math.random() - 1;
  //  f[100][100] = 1;
    G = new double[32][32];
    Lc = 2*Rc;
    double Rc2 = Rc*Rc;
    G[0][0] = 1;
    for (int i = 1; i < Lc; i++){
     G[0][i] = Math.exp(-(i*i/Rc2));
     for (int j = 1; j <= i; j++) G[j][i] = G[0][i]*G[0][j];}
    byte rColor[] = new byte[maxColor+2], bColor[] = new byte[maxColor+2],
         gColor[] = new byte[maxColor+2];
    int M=maxColor/2;
    long M4 = (long)M*M*M*M;
    for (int i = 0; i < M; i++){
      long dum = i;  dum *=dum;  dum *=dum;
      bColor[i] = gColor[M+i] = gColor[M-i] = rColor[maxColor-1-i] =
       (byte)(255 - (255*dum)/M4);}
    gColor[M] = (byte)220;
    rColor[cWhite] = gColor[cWhite] = bColor[cWhite] = (byte)255;
    iColor = new IndexColorModel( 8, maxColor+2, rColor,gColor,bColor);
    hCol = h/maxColor;   hBar = maxColor*hCol;
    int cBar[] = new int[20*hBar], t = 0;
    for (int i = maxColor-1; i >=0; i--)
     for (int j = 0; j < hCol; j++)
      for (int k = 0; k < 20; k++) cBar[t++] = i;
    imBar = createImage(new MemoryImageSource(20, hBar, iColor, cBar, 0, 20));
  
    lbRc = new Label("Rc", Label.RIGHT);  add(lbRc);
    chRc = new Choice();
    for (int i = 0, r = 1; i < 5; i++){
      chRc.addItem(Integer.toString(r));  r *= 2;}
    chRc.select("" + Rc);  chRc.addItemListener(this);  add(chRc);
    btNew = new Button("New");   btNew.addActionListener(this);
    add(btNew);
    s=getParameter("Burn"); if (s != null) bBurn = true;
    cbBurn = new Checkbox("Burn", bBurn);
    add(cbBurn);
    cbBurn.addItemListener(this);
    addMouseMotionListener(this);
    averaging();
  }
  public void destroy(){
   removeMouseMotionListener(this);
  }
  public void averaging(){
    generTime = System.currentTimeMillis();
    double Vmin = 100, Vmax = -100;
    sV = 0;
    int t = 0, w32 = w+32;
    for (int i = 32; i < h+32; i++){
     for (int j = 32; j < w32; j++){
      double s = G[0][0]*f[i][j];
      for (int m = 1; m < Lc; m++){
       int im = i+m, i_m = i-m, jm = j+m, j_m = j-m;
       s += G[0][m]*(f[im][j]+f[i_m][j]+f[i][jm]+f[i][j_m]) +
            G[m][m]*(f[im][jm]+f[i_m][jm]+f[im][j_m]+f[i_m][j_m]);
       for (int n = 1; n < m; n++){
        int in = i+n, i_n = i-n, jn = j+n, j_n = j-n;
        s += G[n][m]*(f[im][jn]+f[i_m][jn]+f[im][j_n]+f[i_m][j_n] +
                      f[in][jm]+f[i_n][jm]+f[in][j_m]+f[i_n][j_m]);}}
      V[t++] = s;
      if (s > Vmax) Vmax = s;
      if (s < Vmin) Vmin = s;
      sV += s;}}
    sV /= w*h;
    Vo = Vmax;  if (Vmax < -Vmin) Vo = -Vmin;
    makeImg();
    generTime = System.currentTimeMillis() - generTime;
  }
  
  public void makeImg(){
    double a = .5*maxColor/Vo, tmp, VpVo = Vp*Vo;
    for (int i = 0; i < w*h; i++)
      if ((tmp = V[i]) < VpVo) iV[i+w] = cWhite;
      else iV[i+w] = (int)(a*(tmp+Vo));
    if ( bBurn ){
      int lastNb = -1;
      for (int i = w; i < 2*w; i++)
        if (iV[i] == cWhite) nb[++lastNb] = i;
      while ( lastNb >= 0){
        int n = nb[lastNb--];
        if (iV[n] == cWhite){
          iV[n] = cBlack;
          for (int i = 0; i < 4; i++){
           int t = n+delNb[i];
           if (iV[t] == cWhite) nb[++lastNb] = t;}}}}
    if ( img != null) img.flush();
    img = createImage(new MemoryImageSource(w, h, iColor, iV, w, w));
  }
  public void paint(Graphics g) {
    g.drawImage(img, 0, lbSize, this);
    g.drawImage(imBar, w+10, lbSize, this);
    g.setColor(Color.white);
    int y = lbSize + (int)(hBar*(1 - sV/Vo)/2); 
    g.drawLine(w+10, y, w+30, y);
    g.setColor(Color.black);
    y = lbSize + (int)(hBar*(1 - Vp)/2); 
    g.drawLine(w+10, y, w+30, y);
    showStatus( "T=" + generTime + "ms ");
  }
  
  public void mouseMoved(MouseEvent e){}
  public void mouseDragged(MouseEvent e) {
    if( e.getX() > w){
      int y = e.getY() - lbSize;
      Vp = 1 - y*2.0/hBar;
      if (Vp < -1) Vp = -1;  if (Vp > 1) Vp = 1;
      makeImg();
      repaint();
    }
  }
  public void itemStateChanged(ItemEvent e){
    Object src = e.getSource();
    if (src == cbBurn){
     bBurn = cbBurn.getState();
     makeImg();}
    if (src == chRc){
     Rc = Integer.parseInt(chRc.getSelectedItem());
     Lc = 2*Rc;
     double Rc2 = Rc*Rc;
     G[0][0] = 1;
     for (int i = 1; i < Lc; i++){
      G[0][i] = Math.exp(-(i*i/Rc2));
      for (int j = 1; j <= i; j++) G[j][i] = G[0][i]*G[0][j];}
     averaging();}
    repaint();
  }
  public void actionPerformed(ActionEvent e){
    for (int i = 0; i < h+64; i++)
     for (int j = 0; j < w+64; j++) f[i][j] = 2*Math.random() - 1;
    averaging();
    repaint();
  }
  public void update(Graphics g){ paint(g); }
  }