// Interactive 2D B-spline, Evgeny Demidov  5 August 2001
import java.awt.*;
import java.awt.event.*;
import java.util.StringTokenizer;

public class @file extends java.applet.Applet
  implements MouseMotionListener{
Image buffImage;          Graphics buffGraphics;
int n=1, k=2, n1, nt, Tmin,Tmax, w,h,h1,w2;
double[] Px,Py, ti;
double N[][];
Color col[];

public void drawFun(){
  double step = (ti[nt-1]-ti[0])/(w2-.9), t = ti[0];
  Color[] iColor = {Color.red, new Color(0f,.7f,0f), Color.blue, Color.magenta,
   new Color(0f,.8f,.8f), new Color(.9f,.9f,0f), Color.gray };
  buffGraphics.clearRect(0,0, w, h);
  Tmin = (int)((ti[k-1]-ti[0])/step) + 1;
  Tmax = (int)((ti[n1]-ti[0])/step);
  int i1 = 0;
  for (int l = 0; l < w2; l++){
   while (t >= ti[i1] ) i1++;
   int i = i1-1;
   col[l] = iColor[(i+8-k) % 7];
   for (int j = 0; j < nt; j++) N[j][l] = 0;
   N[i][l] = 1;

   for (int m = 2; m <= k; m++){        //  basis functions calculation
    int jb = i-m+1;  if (jb < 0) jb = 0;
    for (int j = jb; j <= i; j++){
     N[j][l] = N[j][l]*(t - ti[j])/(ti[j+m-1] - ti[j]) +
      N[j+1][l]*(ti[j+m] - t)/(ti[j+m] - ti[j+1]);}}

   t += step;}
  for (int j = 0; j < n1; j++){
   buffGraphics.setColor(iColor[j % 7]);
   t = ti[0];
   int to = (int)t;
   for (int l = 1; l < w2; l++){
    t += step;
    int t1 = (int)t;
    buffGraphics.drawLine(to, h1-(int)(h1*N[j][l-1]),
     t1, h1-(int)(h1*N[j][l]) );
    to = t1;}}
  for (int l = k; l <= n1; l++){
   buffGraphics.setColor(iColor[(l-k) % 7]);
   buffGraphics.drawLine((int)ti[l-1], 1, (int)ti[l], 1);}
  buffGraphics.setColor(Color.black);
  for (int l = 0; l < nt; l++)
   buffGraphics.drawRect((int)ti[l]-1, 0, 3,3);
}

public void drawSpline(){
  int X,Y;
  buffGraphics.clearRect(0,0, w2, h);
  buffGraphics.setColor(Color.blue);
  for (int i = 0; i < n1; i++){
   X = (int)Px[i];  Y = h1-(int)Py[i];
   buffGraphics.drawRect(X-1,Y-1, 3,3);}
  if ( k > 2 ){
   int Xo = (int)Px[0], Yo = h1-(int)Py[0];
   for (int i = 1; i < n1; i++){
    X = (int)Px[i];  Y = h1-(int)Py[i];
    buffGraphics.drawLine(Xo,Yo, X,Y);
    Xo = X;  Yo = Y;}
  }
  double sX = 0, sY = 0;
  for (int j = 0; j < n1; j++){
   sX += Px[j]*N[j][Tmin];  sY += Py[j]*N[j][Tmin];}
  int Xold = (int)sX, Yold = h1-(int)sY;
  for (int k = Tmin+1; k <= Tmax; k++){
   sX = 0;  sY = 0;
   for (int j = 0; j < n1; j++){
     sX += Px[j]*N[j][k];  sY += Py[j]*N[j][k];}
   X = (int)sX;  Y = h1-(int)sY;
   buffGraphics.setColor(col[k]);
   if ( (X < w2) && (Xold < w2) ) buffGraphics.drawLine(Xold,Yold, X,Y );
   Xold = X; Yold = Y;
  }
}

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){
   StringTokenizer st = new StringTokenizer(s);
   n = Integer.parseInt(st.nextToken());
   k = Integer.parseInt(st.nextToken());}
  n1 = n+1;
  nt = n+k+1;
  Px = new double[n1];  Py = new double[n1];  ti = new double[nt+k];
  col = new Color[w2];
  N = new double[nt+1][w2];
  s=getParameter("pts");
  if (s != null){
   StringTokenizer st = new StringTokenizer(s);
   for (int i = 0; i < n1; i++){
    Px[i] = w2*Double.valueOf(st.nextToken()).doubleValue();
    Py[i] = h1*Double.valueOf(st.nextToken()).doubleValue();}}
  else{ Px[0] = .2*w2; Px[1] = .8*w2;  Py[0] = .8*h1; Py[1] = .2*h1;}
  s=getParameter("knots");
  if (s != null){
   StringTokenizer st = new StringTokenizer(s);
   for (int i = 0; i < nt; i++)
    ti[i] = Double.valueOf(st.nextToken()).doubleValue();}
  else{ ti[0] = 0; ti[1] = 1; ti[2] = 2; ti[3] = 3; }
  double to = ti[0], dt = ti[nt-1]-to;
  for (int i = 0; i < nt; i++) ti[i] = w2 + w2*(ti[i]-to)/dt;
  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 y = h1 - e.getY();  if (y < 0) y = 0;  if (y > h1) y = h1;
  int x = e.getX();
   int iMin = 0;
   double Rmin = 1e10, r2,xi,yi;
  if ( x < w2){
   if (x > w2-10) return;
   if (x < 0) x = 0;
   for (int i = 0; i < n1; 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;}
  else{
   if ( x > w ) x = w;
   for (int i = 0; i < nt; i++)
    if ( (r2 = Math.abs(ti[i]-x) ) < Rmin ){ iMin = i; Rmin = r2;}
   ti[iMin] = x;
   drawFun();}
  drawSpline();
  repaint();
}

public void paint(Graphics g) {
  g.drawImage(buffImage, 0, 0, this);
//  showStatus( " " + x +"  " + y);
}

public void update(Graphics g){ paint(g); }

}