Simple wire framed figure with motion (demo use of Stencil)

Description: 
The main intent of this program is to demo the stencil plane functionality, hence the rendering is kept  simple (wire frame).

Usese:
Right click to choose the motion and the Stencil on/off.

The Project Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <GL/glut.h>
static int stencilOn = 1;
/* function declarations */
void drawScene(void), setMatrix(void), animation(void), resize(int w, int h),
  keyboard(unsigned char c, int x, int y), menu(int choice), drawWireframe(int face),
  drawFilled(int face);
/* global variables */
float ax, ay, az;       /* angles for animation */
/* coords of a cube */
static GLfloat cube[8][3] =
{0.0, 0.0, 0.0,
  1.0, 0.0, 0.0,
  1.0, 0.0, 1.0,
  0.0, 0.0, 1.0,
  1.0, 1.0, 0.0,
  1.0, 1.0, 1.0,
  0.0, 1.0, 1.0,
  0.0, 1.0, 0.0};
static int faceIndex[6][4] =
{0, 1, 2, 3,
  1, 4, 5, 2,
  4, 7, 6, 5,
  7, 0, 3, 6,
  3, 2, 5, 6,
  7, 4, 1, 0};
int main(int argc, char **argv)
{
  glutInit(&argc, argv);
  glutInitWindowSize(400, 400);
  glutInitDisplayMode(GLUT_RGB | GLUT_STENCIL | GLUT_DOUBLE | GLUT_DEPTH);
  glutCreateWindow("Stenciled hidden surface removal");
  ax = 10.0;
  ay = -10.0;
  az = 0.0;
  glutDisplayFunc(drawScene);
  glutReshapeFunc(resize);
  glutCreateMenu(menu);
  glutAddMenuEntry("Motion", 3);
  glutAddMenuEntry("Stencil on", 1);
  glutAddMenuEntry("Stencil off", 2);
  glutAttachMenu(GLUT_RIGHT_BUTTON);
  glutKeyboardFunc(keyboard);
  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}
void drawWireframe(int face)
{
  int i;
  glBegin(GL_LINE_LOOP);
  for (i = 0; i < 4; i++)
    glVertex3fv((GLfloat *) cube[faceIndex[face][i]]);
  glEnd();
}

void drawFilled(int face)
{
  int i;
  glBegin(GL_POLYGON);
  for (i = 0; i < 4; i++)
    glVertex3fv((GLfloat *) cube[faceIndex[face][i]]);
  glEnd();
}
void drawScene(void)
{
  int i;
  glEnable(GL_DEPTH_TEST);
  glDepthFunc(GL_LEQUAL);
  glClearColor(0.0, 0.0, 0.0, 0.0);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glPushMatrix();
  glRotatef(ax, 1.0, 0.0, 0.0);
  glRotatef(-ay, 0.0, 1.0, 0.0);
/* all the good stuff follows */
  if (stencilOn) {
    glEnable(GL_STENCIL_TEST);
    glClear(GL_STENCIL_BUFFER_BIT);
    glStencilMask(1);
    glStencilFunc(GL_ALWAYS, 0, 1);
    glStencilOp(GL_INVERT, GL_INVERT, GL_INVERT);
  }
  glColor3f(1.0, 1.0, 0.0);
  for (i = 0; i < 6; i++) {
    drawWireframe(i);
    if (stencilOn) {
      glStencilFunc(GL_EQUAL, 0, 1);
      glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
    }
    glColor3f(0.0, 0.0, 0.0);
    drawFilled(i);

    glColor3f(1.0, 1.0, 0.0);
    if (stencilOn) {
      glStencilFunc(GL_ALWAYS, 0, 1);
      glStencilOp(GL_INVERT, GL_INVERT, GL_INVERT);
    }
    glColor3f(1.0, 1.0, 0.0);
    drawWireframe(i);
  }
  glPopMatrix();
  if (stencilOn)
    glDisable(GL_STENCIL_TEST);
  /* end of good stuff */
glutSwapBuffers();
}
void setMatrix(void)
{
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-2.0, 2.0, -2.0, 2.0, -2.0, 2.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}
int count = 0;
void animation(void)
{
  /* animate the cone */
  ax += 5.0;
  ay -= 2.0;
  az += 5.0;
  if (ax >= 360)
    ax = 0.0;
  if (ay <= -360)
    ay = 0.0;
  if (az >= 360)
    az = 0.0;
  glutPostRedisplay();
  count++;
  if (count >= 60)
    glutIdleFunc(NULL);
}
void menu(int choice)
{
  switch (choice) {
  case 3:
    count = 0;
    glutIdleFunc(animation);
    break;
  case 2:
    stencilOn = 0;
    glutSetWindowTitle("Stencil Disabled");
    glutPostRedisplay();
    break;
  case 1:
    stencilOn = 1;
    glutSetWindowTitle("Stencil Enabled");
    glutPostRedisplay();
    break;
  }
}
/* ARGSUSED1 */
void keyboard(unsigned char c, int x, int y)
{
  switch (c) {
  case 27:
    exit(0);
    break;
  default:
    break;
  }
}
void resize(int w, int h)
{
  glViewport(0, 0, w, h);
  setMatrix();
}