Hi I have a geometry problem.Can anyone help with java code

Question

Hi I have a non simple polygon . My job is to make it a simple. for that First I need to find the intersecting lines say line AB intersects line CD. If so then I must replace AB & CD with AC & BD or AD or BC which ever keeps the polygon closed . So can anyone help me out with this code
import java.io.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import javax.swing.*;
public class Simple{
static int POINTWID = 4; // size of points
// the x and y arrays hold the coordinates
// the B array is the order of the points in the polygon
// You want to fill the C array with the simple polygon
static double x[] = new double[200];
static double y[] = new double[200];
static int B[] = new int[200]; // the permutation matrix
static int C[] = new int[200]; // the one that becomes simple
static SimpleFrame myFrame;
static int numPoints = 3;
public static void main(String args[]) {
makePolygons();
// Create the frame to draw on
myFrame = new SimpleFrame();
myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myFrame.setSize(600, 600);
myFrame.setVisible(true);
public static void makePolygons(){
// Build an array of random points in the unit square
for(int i = 0; i < numPoints; i++){
x[i] = Math.random();
y[i] = Math.random();// Sample program
B[i] = i; // default permutation
// Create the simple polygon
createSimplePolygon();
* This is the only function you need to mess with
public static void createSimplePolygon(){
// Initialize the C[] array with the identity permutation
for(int i = 0; i < numPoints; i++)
C[i] = i;
// Bubble sort the points from left to right
for(int i = 0; i < numPoints; i++)
for(int j = 0; j < numPoints - 1; j++)
if(x[C[j]] > x[C[j+1]]){
int temp = C[j];
C[j] = C[j+1];
C[j+1] = temp;
public static class SimpleFrame extends JFrame{
public static JSlider numPointsSlider;
public SimpleFrame()
super("Create you own Simple Polygon");
Container content = getContentPane();
content.setLayout(new java.awt.BorderLayout());
JTabbedPane tabbedPane = new JTabbedPane();
tabbedPane.setPreferredSize (new java.awt.Dimension(300, 400));
tabbedPane.addTab("Scrambled", new ScrambledPanel());
tabbedPane.addTab("Simple", new SimplePanel());
content.add(tabbedPane, java.awt.BorderLayout.CENTER);
// Slider for the number of points
numPointsSlider = new JSlider (javax.swing.SwingConstants.HORIZONTAL,
3, 100, 11);
numPointsSlider.addChangeListener (new javax.swing.event.ChangeListener () {
public void stateChanged (javax.swing.event.ChangeEvent evt) {
numPointsSliderStateChanged (evt);
content.add(numPointsSlider, java.awt.BorderLayout.SOUTH);
private void numPointsSliderStateChanged (javax.swing.event.ChangeEvent evt) {
numPoints = numPointsSlider.getValue();
makePolygons();
repaint();
public static class ScrambledPanel extends JPanel{           
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
// First set the scaling to fit the window
Dimension size = getSize();
int Xwid = (int) (0.95 * size.width);
int Ywid = (int) (0.95 * size.height);
// First draw the segments
g2.setColor(Color.red);
for(int i = 0; i < numPoints; i++)
g2.drawLine((int) (Xwid * x[B[i]]),
(int) (Ywid * y[B[i]]),
(int) (Xwid * x[B[(i+1) % numPoints]]),
(int)(Ywid * y[B[(i+1) % numPoints]]));
// Now draw the points
for(int i = 0; i < numPoints; i++){
g2.fillRect((int) (Xwid * x) - POINTWID,
(int) (Ywid * y[i]) - POINTWID,
2*POINTWID + 1, 2*POINTWID + 1);
public static class SimplePanel extends JPanel{
public void paintComponent(Graphics g){
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
// First set the scaling to fit the window
Dimension size = getSize();
int Xwid = (int) (0.95 * size.width);
int Ywid = (int) (0.95 * size.height);
// First draw the segments
g2.setColor(Color.red);
for(int i = 0; i < numPoints; i++)
g2.drawLine((int) (Xwid * x[C[i]]),
(int) (Ywid * y[C[i]]),
(int) (Xwid * x[C[(i+1) % numPoints]]),
(int)(Ywid * y[C[(i+1) % numPoints]]));
// Now draw the points
for(int i = 0; i < numPoints; i++){
g2.fillRect((int) (Xwid * x[i]) - POINTWID,
(int) (Ywid * y[i]) - POINTWID,
2*POINTWID + 1, 2*POINTWID + 1);

Answer 1

Hi I am sorry I could explain you properly . Ok
My program gives me a polygon(as you can see when u
run this program)But the polygon is a non simple
polygon.So to make this polygon we must remove all
the crossings betweeen edges in the polygon.The
algorithm which i gave will remove all the crossings
and make the polygon simple.You did not give an algorithm!
SO my job is to take the
existing code and implement the algorithm for this
program in the Createsimpelpolygon() function. For
this First the program must find whether two edges
cross if they cross then swap the vertices like
replace AB & CD with AC & BD or AD & BC.Which ever
keeps the polygon closed . Still not entirely clear to me. You cannot just go and replace vertexes from a polygon: that way you'll end up with a different polygon.
So as we go on we find the
many crossings and iterate the algorithm on all the
crossings until we get simple polygon.Like I said: I don't really understand what it is you're after. You did not respond to my suggestions, so I gather it is not what you're after?
What about Polygon Tessellation (Google for it)? Perhaps that's what you want.
Also, why do you not create a (or use java.awt's) Point class and a Polygon class which holds a java.util.Set of Point's? Your current code looks rather messy.