// Interactive 2D Bezier splines,  Evgeny Demidov 16 June 2001
  import java.awt.*;
  import java.awt.event.*;
  import java.util.StringTokenizer;
  
  public class applet-math-bezier extends java.applet.Applet
    implements MouseMotionListener{
  Image buffImage;          Graphics buffGraphics;
  int n = 4, n1,  w,h,h1,w2;
  double[] Px,Py;
  
  public void drawFun(){
    double step = 1./w2, t = step;
    double[] B = new double[n1], Bo = new double[n1], Bold = new double[n1];
    B[1] = Bo[1] = h1;
    Color[] iColor = {Color.gray, Color.red, new Color(0f,.7f,0f),
     Color.blue, Color.magenta, new Color(0f,.8f,.8f), new Color(.9f,.9f,0f) };
    for (int k = 1; k < w2; k++){
     System.arraycopy(B,1,Bold,1,n);
     System.arraycopy(Bo,1,B,1,n);
  
     for (int j = 1; j < n; j++)        //  basis functions calculation
      for (int i = j+1; i > 0; i--)
       B[i] = (1-t)*B[i] + t*B[i-1];
  
     for (int m = 1; m <= n; m++){
      buffGraphics.setColor(iColor[m % 7]);
      buffGraphics.drawLine(w2+k-1, h1-(int)Bold[m], w2+k, h1-(int)B[m] );}
     t += step;
    }
  }
  
  public void drawSpline(){
    double step = 1./w2, t = step;
    double[] Pxi = new double[n], Pyi = new double[n];
    int X,Y, Xold = (int)Px[0], Yold = h1-(int)Py[0];
    buffGraphics.clearRect(0,0, w2, h);
    buffGraphics.setColor(Color.blue);
    for (int i = 0; i < n; i++){
     X = (int)Px[i];  Y = h1-(int)Py[i];
     buffGraphics.drawRect(X-1,Y-1, 3,3);}
    if ( n > 2 ){
     int Xo = Xold, Yo = Yold;
     for (int i = 1; i < n; i++){
      X = (int)Px[i];  Y = h1-(int)Py[i];
      buffGraphics.drawLine(Xo,Yo, X,Y);
      Xo = X;  Yo = Y;}
    }
    buffGraphics.setColor(Color.red);
    for (int k = 1; k < w2; k++){
     System.arraycopy(Px,0,Pxi,0,n);
     System.arraycopy(Py,0,Pyi,0,n);
  
     for (int j = n-1; j > 0; j--)        //  points calculation
      for (int i = 0; i < j; i++){
       Pxi[i] = (1-t)*Pxi[i] + t*Pxi[i+1];
       Pyi[i] = (1-t)*Pyi[i] + t*Pyi[i+1];}
  
     X = (int)Pxi[0];  Y = h1-(int)Pyi[0];
     buffGraphics.drawLine(Xold,Yold, X,Y );
     Xold = X; Yold = Y;
     t += step;
    }
  }
  
  public void init() {
    w = Integer.parseInt(getParameter("width"));
    h = Integer.parseInt(getParameter("height"));  h1 = h-1; w2 = w/2;
    String s = getParameter("N"); if (s != null) n = Integer.parseInt(s);
    n1 = n+1;
    Px = new double[n];  Py = new double[n];
    s=getParameter("pts");
    if (s != null){
     StringTokenizer st = new StringTokenizer(s);
     for (int i = 0; i < n; i++){
      Px[i] = w2*Double.valueOf(st.nextToken()).doubleValue();
      Py[i] = h1*Double.valueOf(st.nextToken()).doubleValue();}}
    else{
     Px[0] = .1*w2; Px[1] = .1*w2; Px[2] = .9*w2; Px[3] = .9*w2;
     Py[0] = .1*h1; Py[1] = .9*h1; Py[2] = .9*h1; Py[3] = .1*h1;}
    buffImage = createImage(w, h);
    buffGraphics = buffImage.getGraphics();
    setBackground(Color.white);
    buffGraphics.clearRect(0,0, w, h);
    addMouseMotionListener(this);
    drawFun();
    drawSpline();
  }
  
  public void destroy(){ removeMouseMotionListener(this); }
  public void mouseMoved(MouseEvent e){}  //1.1 event handling
  
  public void mouseDragged(MouseEvent e) {
    int x = e.getX();  if (x < 0) x = 0;  if (x > w2-3) x = w2-3;
    int y = h1 - e.getY();  if (y < 0) y = 0;  if (y > h1) y = h1;
    int iMin = 0;
    double Rmin = 1e10, r2,xi,yi;
    for (int i = 0; i < n; i++){
     xi = (x - Px[i]); yi = (y - Py[i]);
     r2 = xi*xi + yi*yi;
     if ( r2 < Rmin ){ iMin = i; Rmin = r2;}}
    Px[iMin] = x; Py[iMin] = y;
    drawSpline();
    repaint();
  }
  
  public void paint(Graphics g) {
    g.drawImage(buffImage, 0, 0, this);
  //  showStatus( " " + x +"  " + y);
  }
  
  public void update(Graphics g){ paint(g); }
  
  }