[Mesa-dev] first attempt at shader stencil export

Roland Scheidegger sroland at vmware.com
Mon Oct 4 07:43:38 PDT 2010

On 03.10.2010 13:14, Dave Airlie wrote:
>>> No this won't work as you can't read a z24s8 format a i32 (not the same
>>> typeless group, number of components needs to be the same as well as all
>>> components need to have same number of bits).
>>> But the format list suggests this is possible. For z24s8 you could
>>> presumably use DXGI_FORMAT_R24G8_TYPELESS. For depthstencil view it
>>> should be possible to then use DXGI_FORMAT_D24_UNORM_S8_UINT. For
>>> reading depth use DXGI_FORMAT_R24_UNORM_X8_TYPELESS - for reading
>>> stencil similarly use DXGI_FORMAT_X24_TYPELESS_G8_UINT. That's at least
>>> my interpretation. Note you can't read both components at once (there is
>>> no DXGI_FORMAT_R24_UNORM_G8_UINT format), you need different resource
>>> views for that (presumably because the components don't have the same
>>> type, so this is disallowed). Despite that reading depth will return
>>> first (red) component, stencil second (green).
>> Interesting.
>> Gallium should have similar restraints: I recall Dave Airlie saying that
>> AMD's recent ships have separate storage for depth and stencil, and
>> DirectX10 rules accommodate that quite well.
>> This means that Z24_S8 should be disallowed in sampler views: either it
>> is Z24_X8 or X24_S8. And only one component is returned.
>> It also means we need to add X24_S8 formats to gallium.
> Okay I've updated the branch,
> http://cgit.freedesktop.org/~airlied/mesa/log/?h=gallium-stencil-export
> though I need to go back and rebase it so its in-order changes and cleaner.
> I've added the two X24S8/S8X24 formats to gallium, moved to
> and fixed the early Z check in softpipe.
> The state tracker now uses sampler views into the same texture to get
> the values.
> I need to check it works on r600 when I get back to the hw, and add a
> check in the st for the new formats being supported.

I think this is definitely taking the right direction. I only briefly
skimmed through it, but this struck me:
+PIPE_FORMAT_X24S8_USCALED , plain, 1, 1, x24, u8 , , , _x__, zs
+PIPE_FORMAT_S8X24_USCALED , plain, 1, 1, u8 , x24 , , , _y__, zs

I think X24S8 should have swizzle _y__, and S8X24 _x__.


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