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.

And I tried to attach a stencil buffer to FBO, buf the screen turns to black. Here's my code,

   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.

The eglContext is created with STENCIL_SIZE=8, it works without a RTT.

I tried to change the RenderbufferStorage for both depth buffer and stencil buffer, but none of them works.

Is there anything I have missed? Does the stencil buffer pack with depth buffer? (I cannot find things like GL_DEPTH24_STENCIL8 ...)