VERTEX GetRay()
{
  VERTEX P1,P2,direction;
  double length=0;
   GLdouble modelMatrix[16];
   GLdouble projMatrix[16];
   GLint viewport[4];
   GLdouble objx,objy,objz;
  
  glGetDoublev(GL_MODELVIEW_MATRIX,modelMatrix);
  glGetDoublev(GL_PROJECTION_MATRIX,projMatrix);
  glGetIntegerv(GL_VIEWPORT,viewport);
  
  gluUnProject(mouse_x,
               viewport[3] - mouse_y,
               0,
               modelMatrix,
               projMatrix,
               viewport,
               &objx,
               &objy,
               &objz);

  
  P1.x = objx;  P1.y = objy;  P1.z = objz;
  
  gluUnProject(mouse_x,
               viewport[3] - mouse_y,
               1,
               modelMatrix,
               projMatrix,
               viewport,
               &objx,
               &objy,
               &objz);
  
  P2.x = objx;  P2.y = objy;  P2.z = objz;
  direction.x = P2.x - P1.x;
  direction.y = P2.y - P1.y;
  direction.z = P2.z - P1.z;
  
  length = sqrt(direction.x*direction.x + direction.y*direction.y + direction.z*direction.z);
  
  direction.x /= length;
  direction.y /= length;
  direction.z /= length;
  
  return(direction);
}

glLoadIdentity();
 glDisable(GL_TEXTURE_2D);
 Camera.Look();
 glLineWidth(5.0f);
 glColor3f(1,1,1);
 glBegin(GL_LINES);
  glVertex3f(Camera.PositionX(), Camera.PositionY(), Camera.PositionZ() );
  glVertex3f(Camera.PositionX() +  1000*GetRay().x,
             Camera.PositionY() +  1000*GetRay().y, 
             Camera.PositionZ() +  1000*GetRay().z); 
 glEnd();
 glLineWidth(1.0f);