Java Program to Rotate Polygon - 2d Transformation Rotation in Java

This is a java program for rotation transformation in computer graphics. Rotation is one of the important 2d transformations in computer graphics. The program will tell you how to rotate points or polygon around a point (the pivot point). This CG lab program in java language reads the number of sides of polygon, co-ordinates of its vertices, the pivot point for rotation, and angle of rotation. It displays the original polygon and translated polygon in different colors in same screen. This program will tell you how to rotate a polygon in java. I override the paintComponent() method of JPanel to draw on a JPanel.

package javaapplication5;

import java.awt.Color;
import java.awt.Graphics;
import java.util.Scanner;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class RotatePolygon{
static int n;
static int[] xs=new int[20];
static int[] ys=new int[20];
static int i,xp,yp,degree;
static float radian;    

static void rotate()
{
int i;
float t,v;
for(i=0;i<n;i++)
 {
 t=xs[i]-xp;
 v=ys[i]-yp;
 xs[i]=(int)(xp+t*Math.cos(radian)-v*Math.sin(radian));
 ys[i]=(int)(yp+v*Math.cos(radian)+t*Math.sin(radian));
 }
}
    
    
public static void main(String[] args)
{

Scanner sc=new Scanner(System.in);
System.out.println("Enter number of sides: ");
n=sc.nextInt();
System.out.println("Enter co-rdinates: x,y for each point:");
System.out.println("(x between 0 and 640, y between 0 and 360)");
for(i=0;i<n;i++)
    {
    xs[i]=sc.nextInt();
    ys[i]=sc.nextInt();
    }
System.out.println("\nenter pivot point co-ordinate");
xp=sc.nextInt();
yp=sc.nextInt();
System.out.println("\nenter rotation angle");
degree=sc.nextInt();
radian=(float)degree*3.14f/180;
JFrame jf=new JFrame();
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jf.setSize(600,400);
MyPanel panel=new MyPanel();
jf.add(panel);
jf.setVisible(true);
jf.revalidate();
jf.repaint();
}
}


class MyPanel extends JPanel
{
@Override
public void paintComponent(Graphics g)
{
g.setColor(Color.RED);
g.drawPolygon(RotatePolygon.xs, RotatePolygon.ys, RotatePolygon.n);
RotatePolygon.rotate();
g.setColor(Color.BLUE);
g.drawPolygon(RotatePolygon.xs, RotatePolygon.ys, RotatePolygon.n);
}    
}

The above program first reads the polygon. Then original polygon is displayed in red color. Then the translated one is displayed in blue color.

Output:

Enter number of sides: 
4
Enter co-rdinates: x,y for each point:
(x between 0 and 640, y between 0 and 360)
100
100
200
100
200
200
100
200

enter pivot point co-ordinate
200
200

enter rotation angle
60