Write a code to continuously rotate a square about a pivot point. 

  #include  

static GLfloat rotat=0.0;  

void init(void);

void display(void);

void reshape(int w, int h);

void rotate(void);  

int main()

{      

        glutInitDisplayMode(GLUT_RGB|GLUT_DOUBLE);

        glutInitWindowSize(500,500);

        glutInitWindowPosition(100,100);

        glutCreateWindow("Moving squares");

        init();

        glutDisplayFunc(display);

        glutReshapeFunc(reshape);

        glutIdleFunc(rotate);

        glutMainLoop();

}  

void init(void){ 

glClearColour(0.0,0.0,0.0,0.0);

}  

void display(void)

{  glClear(GL_COLOUR_BUFFER_BIT);

   glPushMatrix(); //Push the transformation matrix to stack 

   glTranslatef(-50.0f,-50.0f,0.0); 

   //Translate the pivot point to origin

   glRotatef(rotat,0.0,0.0,1.0); // Rotate about origin

   glTranslatef(50.0f,50.0f,0.0); 

   //Translate pivot point back to its position

   glColour3f(0.0,0.0,1.0); //Set colour of square

   glRectf(-50.0,-50.0,50.0,50.0); //Draw square 

   glPopMatrix(); //Pop the matrix from stack

   glutSwapBuffers(); // Swap buffers

}  

void reshape(int w, int h)

{        glViewport(0,0,(GLsizei)w,(GLsizei)h);

        glMatrixMode(GL_PROJECTION);

        glLoadIdentity();

        glOrtho(-250.0,250.0,-250.0,250.0,-1.0,1.0);

        glMatrixMode(GL_MODELVIEW);

        glLoadIdentity();

}  

void rotate(void)

{     rotat+=0.1; //Continuously increse the rotation angle by 0.1

                if(rotat>360.0)

                        rotat-=360.0;

        glutPostRedisplay(); //send the current window for

redisplay

}