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.

Java Program to Simulate Motion of Simple Pendulum

This is a java program to simulate motion of simple pendulum using java graphics. This was a problem given in computer graphics lab, which i was supposed to do using graphics.h header file in C. This is the java version of the same. If you are looking for a C Program, here it is: C Program to Simulate Simple Pendulum Motion - Computer Graphics Lab.

Output is as follows:

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;


public class JavaApplication1 extends JFrame{

    int pivotx,pivoty;
    double thetamax,theta;;
    double len=260;
    int x,y,ymax,xmax;
    int bobradius=30;
    int xsign=-1,ysign=1;
    double omega;
    
    public JavaApplication1()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(600,400);
        thetamax=60*Math.PI/180;
        pivotx=getWidth()/2;
        pivoty=40;
        ymax=(int) (pivoty+len*Math.cos(thetamax));
        xmax=(int) (pivotx+len*Math.sin(thetamax));
        x=xmax;
        y=ymax;
        theta=thetamax;
        System.out.println("pivotx:"+pivotx+" pivoty:"+pivoty);
        System.out.println("starting x:"+x+ "y:"+y);
        System.out.println("starting theta="+theta);
        t.start();
    }

    @Override
    public void paint(Graphics g) {
        System.out.println("called");        
        g.setColor(Color.WHITE);
        g.fillRect(0, 0,getWidth(),getHeight());
        g.setColor(Color.red);
        g.fillOval(pivotx-4,pivoty-4,8,8);
        g.drawLine(pivotx,pivoty, x,y);
        g.fillOval(x-bobradius/2,y-bobradius/2,bobradius,bobradius);
        
    }
    
    Thread t=new Thread()
    {
      public void run()
      {
    try {
      while(true)
      {
      if(x>=pivotx+Math.abs(len*Math.sin(thetamax)))
        {
        System.out.println("right extreme");
        xsign=-1;
        ysign*=-1;
        x=xmax-1;
        Thread.sleep(40);
        }
      else if(x<=pivotx-Math.abs(len*Math.sin(thetamax)))
      {
          System.out.println("left extreme");
          ysign*=-1;
          xsign=1;
          x=(int) (pivotx-Math.abs(len*Math.sin(thetamax))+2);
          Thread.sleep(40);
      }
      else if(y>=pivoty+len)
        {
              ysign*=-1;
              System.out.println("mean position");
        }

      omega=y/60*Math.PI/180;
      double decr=xsign*omega;
          System.out.println("decrement:"+decr);
      theta=theta+decr;
      x=(int) (pivotx+len*Math.sin(theta));
      y=(int) (pivoty+len*Math.cos(theta));
          System.out.println("new theta:"+theta);
      repaint();
      Thread.sleep(40);
    
      }
            } catch (InterruptedException ex) {}
      }
    };
    
    
    public static void main(String[] args) {
        new JavaApplication1().setVisible(true);
    }
    
}