#include <GL/glut.h>
   #include <stdio.h>

   const GLint pickBuffSize = 32;

   /*  Set initial display-window size.  */
   GLsizei winWidth = 400, winHeight = 400;


   void init (void)
   {
      /*  Set display-window color to white.  */
      glClearColor (1.0, 1.0, 1.0, 1.0);
   }

   /*  Define 3 rectangles and associated IDs.  */
   void rects (GLenum mode)
   {
      if (mode == GL_SELECT)
         glPushName (30);         //  Red rectangle.
      glColor3f (1.0, 0.0, 0.0);
      glRecti (40, 130, 150, 260);

      if (mode == GL_SELECT)
         glPushName (10);         //  Blue rectangle.
      glColor3f (0.0, 0.0, 1.0);
      glRecti (150, 130, 260, 260);

      if (mode == GL_SELECT)
         glPushName (20);         //  Green rectangle.
      glColor3f (0.0, 1.0, 0.0);
      glRecti (40, 40, 260, 130);
   }

   /*  Print the contents of the pick buffer for each mouse selection.  */
   void processPicks (GLint nPicks, GLuint pickBuffer [ ])
   {
      GLint j, k;
      GLuint objID, *ptr;

      printf (" Number of objects picked = %d\n", nPicks);
      printf ("\n");
      ptr = pickBuffer;

      /*  Output all items in each pick record.  */
      for (j = 0; j < nPicks; j++) {
         objID = *ptr;

         printf ("   Stack position = %d\n", objID);
         ptr++;

         printf ("   Min depth = %g,", float (*ptr/0x7fffffff));
         ptr++;

         printf ("   Max depth = %g\n", float (*ptr/0x7fffffff));
         ptr++;

         printf ("   Stack IDs are: \n");
         for (k = 0; k < objID; k++) {
            printf ("   %d ",*ptr);
            ptr++;
         }
         printf ("\n\n");
      }
   }

   void pickRects (GLint button, GLint action, GLint xMouse, GLint yMouse)
   {
      GLuint pickBuffer [pickBuffSize];
      GLint nPicks, vpArray [4];

      if (button != GLUT_LEFT_BUTTON || action != GLUT_DOWN)
         return;

      glSelectBuffer (pickBuffSize, pickBuffer);  //  Designate pick buffer.
      glRenderMode (GL_SELECT);             //  Activate picking operations.
      glInitNames ( );                   //  Initialize the object-ID stack.

      /*  Save current viewing matrix.  */
      glMatrixMode (GL_PROJECTION);
      glPushMatrix ( );
      glLoadIdentity ( );

      /*  Obtain the parameters for the current viewport.  Set up 
       *  a 5 by 5 pick window, and invert the input yMouse value 
       *  using the height of the viewport, which is the fourth 
       * element of vpArray.  
       */
      glGetIntegerv (GL_VIEWPORT, vpArray);
      gluPickMatrix (GLdouble (xMouse), GLdouble (vpArray [3] - yMouse),
                        5.0, 5.0, vpArray);

      gluOrtho2D (0.0, 300.0, 0.0, 300.0);
      rects (GL_SELECT);       // Process the rectangles in selection mode.

      /*  Restore original viewing matrix.  */
      glMatrixMode (GL_PROJECTION);
      glPopMatrix ( );

      glFlush ( );

      /*  Determine the number of picked objects and return to the 
       *  normal rendering mode.  
       */
      nPicks = glRenderMode (GL_RENDER);

      processPicks (nPicks, pickBuffer);  // Process picked objects.

      glutPostRedisplay ( );
   }

   void displayFcn (void)
   {
      glClear (GL_COLOR_BUFFER_BIT);
      rects (GL_RENDER);                // Display the rectangles.
      glFlush ( );
   }

   void winReshapeFcn (GLint newWidth, GLint newHeight)
   {
      /*  Reset viewport and projection parameters.  */
      glViewport (0, 0, newWidth, newHeight);
      glMatrixMode (GL_PROJECTION);
      glLoadIdentity ( );

      gluOrtho2D (0.0, 300.0, 0.0, 300.0);
      glMatrixMode (GL_MODELVIEW);

      /* Reset display-window size parameters.  */
      winWidth  = newWidth;
      winHeight = newHeight;
   }

   void main (int argc, char** argv)
   {
      glutInit (&argc, argv);
      glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
      glutInitWindowPosition (100, 100);
      glutInitWindowSize (winWidth, winHeight);
      glutCreateWindow ("Example Pick Program");

      init ( );
      glutDisplayFunc (displayFcn);
      glutReshapeFunc (winReshapeFcn);
      glutMouseFunc (pickRects);

      glutMainLoop ( );
}