#include <GL/glut.h>

   class wcPt2D { 
      public:
         GLfloat x, y; 
   };

   void init (void)
   {
      /*  Set color of display window to white.  */
      glClearColor (1.0, 1.0, 1.0, 0.0);       

      /*  Set parameters for world-coordinate clipping window.  */
      glMatrixMode (GL_PROJECTION);
      gluOrtho2D (-100.0, 100.0, -100.0, 100.0);

      /*  Set mode for constructing geometric transformation matrix.  */
      glMatrixMode (GL_MODELVIEW); 
   }

   void triangle (wcPt2D *verts)
   {
      GLint k;

      glBegin (GL_TRIANGLES);
         for (k = 0; k < 3; k++)
            glVertex2f (verts [k].x, verts [k].y);
      glEnd ( );
   }

   void displayFcn (void)
   {
      /*  Define initial position for triangle.  */
      wcPt2D verts [3] = { {-50.0, -25.0}, {50.0, -25.0}, {0.0, 50.0} };

      glClear (GL_COLOR_BUFFER_BIT);   //  Clear display window.

      glColor3f (0.0, 0.0, 1.0);       //  Set fill color to blue.
      glViewport (0, 0, 300, 300);     //  Set left viewport.
      triangle (verts);                //  Display triangle.

      /*  Rotate triangle and display in right half of display window.  */
      glColor3f (1.0, 0.0, 0.0);         //  Set fill color to red. 
      glViewport (300, 0, 300, 300);     //  Set right viewport.  
      glRotatef (90.0, 0.0, 0.0, 1.0);   //  Rotate about z axis.  
      triangle (verts);           //  Display red rotated triangle.

      glFlush ( );
   }

   void main (int argc, char ** argv)
   {
      glutInit (&argc, argv);
      glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
      glutInitWindowPosition (50, 50);
      glutInitWindowSize (600, 300);
      glutCreateWindow ("Split-Screen Example");

      init ( );
      glutDisplayFunc (displayFcn);
 
      glutMainLoop ( );
   }