[Mesa-dev] gallium separate depth and stencil

[Marek Olšák]

Manual interleaving and deinterleaving in the driver seems to be the
easiest solution. You just need 2 blits. You can reuse u_blitter for
setting up stuff or you can create your own thing.

Adding separate Z+S to Gallium and st/mesa would be quite a lot work,
and what you want to support is an interleaved format anyway. I
suppose you wouldn't be exposing separate formats to applications, you
just want a way to convert an interleaved ZS to separate buffers for
your driver.

We don't plan to expose separate Z+S to applications due to tiling
restrictions on Radeon.

Marek


On Wed, Mar 18, 2015 at 4:52 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> Hello,
>
> I've run into a situation where a3xx hardware does not natively
> support Z32F_S8 (interleaved). However it will happily support Z32F
> and S8 separately (and at the same time). Haven't looked at how a4xx
> handles this, but wouldn't be surprised if it were the same.
>
> One way to do this is to expose the Z32F_X24S8 format in the driver,
> but internally just store the two sets of data separately. Then add
> hooks to the transfer logic to interleave/deinterleave the data on
> transfer in/out. This seems hacky.
>
> Another approach is to teach gallium about split depth/stencil
> buffers, i.e. adding a pipe_surface *sbuf next to the zsbuf. Then,
> guarded by a PIPE_CAP, the st would be able to make use of it. Both
> for binding separate depth/stencil textures (e.g. Z16 + S8), as well
> as to create adapters for this situation. I guess it'd still be a bit
> of a hack, but at least it would be reusable by other hw.
>
> Is there any other hw out there that would need this? Any preferences
> on how I should approach it?
>
> FTR, Z32F_X24S8 is needed for both GL3 (ARB_depth_buffer_float) and GLES3.
>
> Cheers,
>
>   -ilia
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