Bezier.java

//This applet draws a Bezier curve after user gives the control points
//The Bezier curve is redrawn when user clicks on and moves on of the
//control points
import java.awt.*;
import java.applet.Applet;
public class Bezier extends Applet {

Point[] coordlist;

//the control points

int numpoints;

//number of control points

Image offscreenImg;

//used for double buffering

Graphics offscreenG;

double t;

//the time interval

double k = .025;

//time step value for drawing curve

int moveflag = 5;

//flag to notify if user is moving a point

Button restart;

boolean poly = true;

//flag to draw control polygon and points

Button polygon;

public void init() {

//Create coordinate list

coordlist = new Point[4];

numpoints = 0;

//Create offscreen buffer

offscreenImg = createImage(size().width,size().height);

offscreenG = offscreenImg.getGraphics();

//add buttons to screen

restart = new Button("Restart");

add(restart);

polygon = new Button("Polygon");

add(polygon);

}

//this method is called internally by repaint()

public void update(Graphics g) {

paint(g);

}

public void paint(Graphics g) {

//prepare screen

setBackground(Color.white);

offscreenG.setColor(Color.black);

offscreenG.clearRect(0,0,size().width,size().height);

//Draw control points and polygon

if(poly) {

for(int i=0;i<numpoints;i++) {

offscreenG.fillOval(coordlist[i].x-2,

coordlist[i].y-2,4,4);

if(numpoints>1 && i<(numpoints-1))

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Bezier.java

offscreenG.drawLine(coordlist[i].x,coordlist[i].y,

coordlist[i+1].x,coordlist[i+1].y);

}

}

//Calculate and draw bezier curve

if(numpoints == 4) {

double x1,x2,y1,y2;

x1 = coordlist[0].x;

y1 = coordlist[0].y;

for(t=k;t<=1+k;t+=k){

//use Berstein polynomials

x2=(coordlist[0].x+t*(-coordlist[0].x*3+t*(3*coordlist[0].x-

coordlist[0].x*t)))+t*(3*coordlist[1].x+t*(-6*coordlist[1].x+

coordlist[1].x*3*t))+t*t*(coordlist[2].x*3-coordlist[2].x*3*t)+

coordlist[3].x*t*t*t;

y2=(coordlist[0].y+t*(-coordlist[0].y*3+t*(3*coordlist[0].y-

coordlist[0].y*t)))+t*(3*coordlist[1].y+t*(-6*coordlist[1].y+

coordlist[1].y*3*t))+t*t*(coordlist[2].y*3-coordlist[2].y*3*t)+

coordlist[3].y*t*t*t;

//draw curve

offscreenG.drawLine((int)x1,(int)y1,(int)x2,(int)y2);

x1 = x2;

y1 = y2;

}

}

g.drawImage(offscreenImg,0,0,this);

}
//check if user presses either button
public boolean action(Event e, Object o) {

if (e.target == restart) {

//start all over with no points

numpoints = 0;

repaint();

poly = true;

return true;

}

else if(e.target == polygon) {

if(poly)

poly = false;

else

poly = true;

repaint();

return true;

}

return false;

}
public boolean mouseDown(Event evt, int x, int y) {

//Store point in array

Point point = new Point(x,y);

//if there are less than four points, add another one

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Bezier.java

if(numpoints < 4) {

coordlist[numpoints] = point;

numpoints++;

repaint();

}

//otherwise, check if user is trying to click on old point

else

for(int i=0;i<numpoints;i++)

for(int j=-2;j<3;j++)

for(int l=-2;l<3;l++)

if(point.equals(new Point(coordlist[i].x+j,

coordlist[i].y+l)))

moveflag = i;

return true;

}

public boolean mouseDrag(Event evt, int x, int y) {

//check if user is trying to drag an old point

if(moveflag < numpoints) {

coordlist[moveflag].move(x,y);

repaint();

}

return true;

}

public boolean mouseUp(Event evt, int x, int y) {

moveflag = 5;

return true;

}

}

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