//Bezier Curve Algorithm
//User chooses four points of the graphic canvas (by clicking mouse button) that will describe cubic bezier curve. 
//Finally the curve will be drawn. User can also move with created points and so change shape of the curve.

import java.awt.*;
import java.applet.Applet;

public class BezierCurve extends Applet { 		
  Point[] points; //control points
  int number = 0; //control points counter
  Image buffer;	//image buffer
  Graphics gfx; //graphics
  double p;	//parameter
  int moving = 5; //flag to notify if user is moving a point
  double x1,x2,y1,y2; //temporary coordinates
	
  public void init() {
	points = new Point[4];
	buffer = createImage(size().width,size().height); //create graphic buffer
	gfx = buffer.getGraphics();
	gfx.setColor(Color.white);
	gfx.fillRect(0, 0, size().width, size().height);
	setBackground(Color.white);
  }
  
  public void bernstein() {
	for(int i=0; i<=100;i++) { //Berstein polynomials
	  p=(double)i/100.0d;
	  x2=(points[0].x+p*(-points[0].x*3+p*(3*points[0].x-
	      points[0].x*p)))+p*(3*points[1].x+p*(-6*points[1].x+
		  points[1].x*3*p))+p*p*(points[2].x*3-points[2].x*3*p)+
		  points[3].x*p*p*p;
      y2=(points[0].y+p*(-points[0].y*3+p*(3*points[0].y-
	      points[0].y*p)))+p*(3*points[1].y+p*(-6*points[1].y+
	      points[1].y*3*p))+p*p*(points[2].y*3-points[2].y*3*p)+
	      points[3].y*p*p*p;
	  gfx.drawLine((int)x1,(int)y1,(int)x2,(int)y2); //bezier curve
	  x1 = x2;
	  y1 = y2;
	}  
  }
  
  public void paint(Graphics g) { //paint
	gfx.setColor(Color.white);
	gfx.clearRect(0,0,size().width,size().height); //repaint background
	
	if(number == 4) {  
	  x1 = points[0].x;
	  y1 = points[0].y;
	  
	  for(int i=0; i<number;i++) {
		if(number>1 && i<(number-1) && i!=1) {
		  gfx.setColor(Color.lightGray);  
		  gfx.drawLine(points[i].x,points[i].y,points[i+1].x,points[i+1].y); //control handles
		}
	  }
	  
	  gfx.setColor(Color.black);
	  bernstein();  
    }
	
	for(int i=0; i<number;i++) {
	  gfx.setColor(Color.orange);
	  gfx.fillOval(points[i].x-5,points[i].y-5,10,10); //control points
	}
	g.drawImage(buffer,0,0,this);
  }
  
  public boolean mouseDown(Event evt, int x, int y) { //add points
	Point point = new Point(x,y);
	if(number < 4) {
	  points[number++] = point;
	  repaint();
	} else
	  for(int i=0;i<number;i++) 
	    for(int j=-5;j<6;j++)
	      for(int l=-5;l<6;l++)
	        if(point.equals(new Point(points[i].x+j,
	          points[i].y+l)))
	          moving = i;
	return true;
	}
  
  public boolean mouseDrag(Event evt, int x, int y) { //move added points
	if(moving < number) { //can't move point out of canvas
	  if (x>size().width) x=size().width-5;
	  if (x<0) x=5;
	  if (y>size().height) y=size().height-5;
	  if (y<0) y=5;
	  points[moving].move(x,y);
	  repaint();
	}
	return true;
  }
	
  public boolean mouseUp(Event evt, int x, int y) { 
	moving = 5;
	repaint();
	return true;
  }	
  
  public void update(Graphics g) { //update
	paint(g);
  }
}