[Mesa-dev] [PATCH 1/6] mesa: Add field gl_renderbuffer.Unwrapped

[Alex Deucher]

On Wed, Jun 15, 2011 at 9:09 PM, Chad Versace <chad at chad-versace.us> wrote:
> If a renderbuffer wraps multiple renderbuffers, then Unwrapped points to
> the them.
>
> For example, if hardware requires separate depth and stencil buffers
> (X8_Z24 and S8), then glRenderbufferStorage(GL_DEPTH24_STENCIL8) may
> create a fake S8_Z24 renderbuffer for which Unwrapped[BUFFER_DEPTH] and
> Unwrapped[BUFFER_STENCIL] point to the real X8_Z24 and S8 renderbuffers.
>

FWIW, evergreen and newer chips only support separate stencil and
depth, so we had a similar issue.  We ended up using
GL_ARB_shader_stencil_export to implement writes to the stencil.
Start of the thread:
http://lists.freedesktop.org/archives/mesa-dev/2010-September/003318.html

Alex