#include <GL/glut.h>

   GLsizei winWidth = 400, winHeight = 300;   // Initial display-window size.
   GLint endPtCtr = 0;                   // Initialize line endpoint counter.

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

   void init (void)
   {
      glClearColor (0.0, 0.0, 1.0, 1.0)   // Set display-window color to blue.

      glMatrixMode (GL_PROJECTION);
      gluOrtho2D (0.0, 200.0, 0.0, 150.0);
   }

   void displayFcn (void)
   {
      glClear (GL_COLOR_BUFFER_BIT);
   }

   void winReshapeFcn (int newWidth, int newHeight)
   {
      /*  Reset viewport and projection parameters  */
      glViewport (0, 0, newWidth, newHeight);
      glMatrixMode (GL_PROJECTION);
      glLoadIdentity ( );
      gluOrtho2D (0.0, GLdouble (newWidth), 0.0, GLdouble (newHeight));

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

   void drawLineSegment (scrPt endPt1, scrPt endPt2)
   {
      glBegin (GL_LINES);
         glVertex2i (endPt1.x, endPt1.y);
         glVertex2i (endPt2.x, endPt2.y);
      glEnd ( );
   }

   void polyline (GLint button, GLint action, GLint xMouse, GLint yMouse)
   {
      static scrPt endPt1, endPt2;

      if (ptCtr == 0) {
         if (button == GLUT_LEFT_BUTTON && action == GLUT_DOWN) {
            endPt1.x = xMouse;
            endPt1.y = winHeight - yMouse;
            ptCtr = 1;
         }
         else
            if (button == GLUT_RIGHT_BUTTON)        // Quit the program.
               exit (0);
      }
      else
         if (button == GLUT_LEFT_BUTTON && action == GLUT_DOWN) {
            endPt2.x = xMouse;
            endPt2.y = winHeight - yMouse;
            drawLineSegment (endPt1, endPt2);

            endPt1 = endPt2;
         }
         else
            if (button == GLUT_RIGHT_BUTTON)        // Quit the program.
               exit (0);

      glFlush ( );
   }

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

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

      glutMainLoop ( );
   }