#include <GL/glut.h>
#include <math.h>
#include <stdlib.h>

const double TWO_PI = 6.2831853;

GLsizei winWidth = 500, winHeight = 500;    // Initial display window size.
GLuint regHex;                            //  Define name for display list.
static GLfloat rotTheta = 0.0;

class scrPt {
public:
    GLint x, y;
};

static void init (void)
{
   scrPt hexVertex;
   GLdouble hexTheta;
   GLint k;

   glClearColor (1.0, 1.0, 1.0, 0.0);

   /*  Set up a display list for a red regular hexagon.
    *  Vertices for the hexagon are six equally spaced
    *  points around the circumference of a circle.
    */
   regHex = glGenLists (1);
   glNewList (regHex, GL_COMPILE);
      glColor3f (1.0, 0.0, 0.0);
      glBegin (GL_POLYGON);
         for (k = 0; k < 6; k++) {
            hexTheta = TWO_PI * k / 6;
            hexVertex.x = 150 + 100 * cos (hexTheta);
            hexVertex.y = 150 + 100 * sin (hexTheta);
            glVertex2i (hexVertex.x, hexVertex.y);
         }
      glEnd ( );
   glEndList ( );
}

void displayHex (void)
{
   glClear (GL_COLOR_BUFFER_BIT);

   glPushMatrix ( );
   glRotatef (rotTheta, 0.0, 0.0, 1.0);
   glCallList (regHex);
   glPopMatrix ( );

   glutSwapBuffers ( );

   glFlush ( );
}

void rotateHex (void)
{
   rotTheta += 3.0;
   if (rotTheta > 360.0)
      rotTheta -= 360.0;

   glutPostRedisplay ( );
}

void winReshapeFcn (int newWidth, int newHeight)
{
   glViewport (0, 0, (GLsizei) newWidth, (GLsizei) newHeight);

   glMatrixMode (GL_PROJECTION);
   glLoadIdentity ( );
   gluOrtho2D (-320.0, 320.0, -320.0, 320.0);

   glMatrixMode (GL_MODELVIEW);
   glLoadIdentity ( );

   glClear (GL_COLOR_BUFFER_BIT);
}

void mouseFcn (int button, int action, int x, int y)
{
   switch (button) {
      case GLUT_MIDDLE_BUTTON:           //  Start the rotation.
         if (action == GLUT_DOWN)
            glutIdleFunc (rotateHex);
         break;
      case GLUT_RIGHT_BUTTON:            //  Stop the rotation.
         if (action == GLUT_DOWN)
            glutIdleFunc (NULL);
         break;
      default:
         break;
   }
}

void main (int argc, char** argv)
{
   glutInit (&argc, argv);
   glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
   glutInitWindowPosition (150, 150);
   glutInitWindowSize (winWidth, winHeight);
   glutCreateWindow ("Animation Example");

   init ( );
   glutDisplayFunc (displayHex);
   glutReshapeFunc (winReshapeFcn);
   glutMouseFunc (mouseFcn);

   glutMainLoop ( );
}