title: How to create a FBO with stencil buffer in OpenGL ES 2.0?
body: <p>I need stencil buffer on 3GS to render planar shadow, and polygon
  offset won't work prefect, still has z-fighting problem. So I use
  stencil buffer to make the shadow correct, it works on win32 gles2
  emulator, but not on iPhone. After I added a post effect to the whole
  scene. The stencil buffer won't work even on win32 gles2 emulator.</p>
  
  <p>And I tried to attach a stencil buffer to FBO, buf the screen turns to
  black. Here's my code,</p>
  
  <pre>
     glGenRenderbuffers(1, &dbo); // depth buffer
     glBindRenderbuffer(GL_RENDERBUFFER, dbo);
     glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24_OES,
  widthGL, heightGL);
  
     glGenRenderbuffers(1, &sbo); // stencil buffer
     glBindRenderbuffer(GL_RENDERBUFFER, sbo);
     glRenderbufferStorage(GL_RENDERBUFFER, GL_STENCIL_INDEX8, widthGL,
  heightGL);
  
     glGenFramebuffers(1, &fbo);
     glBindFramebuffer(GL_FRAMEBUFFER, fbo);
  
     glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
  GL_TEXTURE_2D, tex, 0);
     glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
  GL_RENDERBUFFER, dbo);
     glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT,
  GL_RENDERBUFFER, sbo); // this make the whole screen black.
  </pre>
  
  <p>The eglContext is created with STENCIL_SIZE=8, it works without a RTT.</p>
  
  <p>I tried to change the RenderbufferStorage for both depth buffer and
  stencil buffer, but none of them works.</p>
  
  <p>Is there anything I have missed? Does the stencil buffer pack with
  depth buffer? (I cannot find things like GL_DEPTH24_STENCIL8 ...)</p>