rotate_polygon.cpp

#include <windows.h>
 #include <gl/Gl.h>
 #include <gl/glut.h>
 #include <cmath>

 int screenheight = 600;
 int screenwidth = 800;
 bool flag = true;
 int first = 0;

 double angle = 30;
 //The angle for the rotation (in degrees)
 typedef struct{
   float x;
   float y;
 }Point2D;

 Point2D p1,p2,p3,p4;

 void DrawPolygonSegment(Point2D pt1, Point2D pt2, Point2D pt3, Point2D pt4){
     glPointSize(1.0);
        glBegin(GL_POLYGON);
             glVertex2i(pt1.x, pt1.y);
             glVertex2i(pt2.x, pt2.y);
             glVertex2i(pt3.x, pt3.y);
             glVertex2i(pt4.x, pt4.y);
     glEnd();

     glPointSize(6.0);
     glBegin(GL_POINTS);
       glVertex2i(pt2.x, pt2.y);
        glVertex2i(pt3.x, pt3.y);
        glVertex2i(pt4.x, pt4.y);
     glEnd();
     glFlush();

 }

 Point2D rotate(Point2D p, float ang){
   ang = ang * 3.14 / 180.0;                 //angle in radians
   Point2D ptemp;

   ptemp.x = p.x * cos(ang) - p.y * sin(ang);
   ptemp.y = p.x * sin(ang) + p.y * cos(ang);

      return ptemp;
 }

 void myMouse(int button, int state, int x, int y) {
     if(state == GLUT_DOWN) {
        if(button == GLUT_LEFT_BUTTON) {
            glClear(GL_COLOR_BUFFER_BIT);

                           switch(first)
                               {
                               case 0:
                                     p1.x = x;
                                     p1.y =screenheight - y;
                                    first = 1;
                                    break;
                               case 1:
                                    p2.x = x;
                                    p2.y = screenheight - y;
                                    first = 2;
                                    break;
                               case 2:
                                    p3.x = x;
                                    p3.y = screenheight - y;
                                    first = 3;
                                    break;
                               case 3:
                                    p4.x = x;
                                    p4.y = screenheight - y;
                                    DrawPolygonSegment(p1,p2,p3,p4);
                                    first = 0;
                                    break;
                               }

        }
        else if (button == GLUT_RIGHT_BUTTON) {
            Point2D Rotated_p1 = rotate(p1,angle);
          Point2D Rotated_p2 = rotate(p2,angle);
            Point2D Rotated_p3 = rotate(p3,angle);
            Point2D Rotated_p4 = rotate(p4,angle);
          DrawPolygonSegment(Rotated_p1,Rotated_p2,Rotated_p3,Rotated_p4);
        }
     }
 }


 void myDisplay(){
     glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
     glClear(GL_COLOR_BUFFER_BIT);
     glColor3f(0.0f, 0.0f, 0.0f);
 }

 int main( int argc, char ** argv ) {
     glutInit( &argc, argv );
     glutInitWindowPosition( 0, 0 );
     glutInitWindowSize( 800, 600 );
     glutCreateWindow( "Rotate Polygon" );
        glMatrixMode( GL_PROJECTION );
     glLoadIdentity();
     gluOrtho2D( 0, 800, 0, 600 );
     glViewport(0, 0, 800, 600);

     glutDisplayFunc( myDisplay );
     glutMouseFunc( myMouse );

     glutMainLoop();
     return( 0 );
 }