How to add separator to context menus in OpenGL/GLUT

This has little to do with "Game Programming" but it's OpenGL/GLUT related and maybe this is the best forum section for such question. If not, please move it appropriately.

Normally this would be something like:

Code:

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glutAddMenuEntry("-", <opid>);

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But it doesn't work. Fater 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:

Code:

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glutAddMenuEntry("-", 0);

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or

Code:

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glutAddMenuEntry("-", -1);

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But neither worked...

Full code example below:

Code:

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    #include <math.h>
   
    #include <GL/glut.h>
   
    #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(&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();
    }

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I don't see a separator like Windows does for other items, instead I see the menu item label as a dash.