title: How to add separator to context menus in OpenGL/GLUT
body: <p>Normally this would be something like:</p>
  
  <pre><code>glutAddMenuEntry("-", &lt;opid&gt;);
  </code></pre>
  
  <p>But it doesn't work. After looking it up on Google I couldn't find much information about this, maybe it's not possible using GLUT? I found a couple of examples like:</p>
  
  <pre><code>glutAddMenuEntry("-", 0);
  </code></pre>
  
  <p>or</p>
  
  <pre><code>glutAddMenuEntry("-", -1);
  </code></pre>
  
  <p>But neither worked...</p>
  
  <pre><code>#include &lt;math.h&gt;
  
  #include &lt;GL/glut.h&gt;
  
  #define WINDOW_WIDTH  640
  #define WINDOW_HEIGHT 480
  
  void changeSize(int w, int h) {
      if(h == 0) h = 1;
  
      float ratio = 1.0 * w / h;
  
      glMatrixMode(GL_PROJECTION);
      glLoadIdentity();
  
      glViewport(0, 0, w, h);
  
      gluPerspective(45.0f, ratio, 1.0f, 1000.0f);
  
      glMatrixMode(GL_MODELVIEW);
  }
  
  void renderScene(void) {
      glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
      glLoadIdentity();
  
      gluLookAt(
          0.0, 0.0, 5.0,
          0.0, 0.0, 0.0,
          0.0f, 1.0f, 0.0f
      );
  
      glutWireTeapot(1.0);
  
      glutSwapBuffers();
  }
  
  void processMenuEvents(int option) {
  }
  
  void main(int argc, char **argv) {
      glutInit(&amp;argc, argv);
      glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
      glutInitWindowPosition(
          (glutGet(GLUT_SCREEN_WIDTH) - WINDOW_WIDTH) / 2,
          (glutGet(GLUT_SCREEN_HEIGHT) - WINDOW_HEIGHT) / 2
      );
      glutInitWindowSize(WINDOW_WIDTH, WINDOW_HEIGHT);
      glutCreateWindow("Camera Demo");
  
      glutDisplayFunc(renderScene);
      glutReshapeFunc(changeSize);
  
      glutCreateMenu(processMenuEvents);
  
      glutAddMenuEntry("OPTION 1", 1);
      glutAddMenuEntry("-", -1);
      glutAddMenuEntry("OPTION 2", 2);
  
      glutAttachMenu(GLUT_RIGHT_BUTTON);
  
      glEnable(GL_DEPTH_TEST);
      glEnable(GL_CULL_FACE);
  
      glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
  
      glutMainLoop();
  }
  </code></pre>
  
  <p>I don't see separator like Windows does for other items, instead I see the menu item label as a dash.</p>