[Mesa-dev] depth writing and missing something

[Corbin Simpson]

Just realized that the texture format table in question is in the TGSI
doc page, at the bottom. It really should have its own page.

~ C.

On Wed, Sep 29, 2010 at 11:36 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
> Sorry, I've should have drunk my morning coffee before replying.
>
> You're refferring to writing and not reading...
>
> Anyway, my comment for u_format still stands.
>
> But back to your example, it works because out[0] has position semantic. When writing to depth textures, their are bound as depth stencil buffer. Not in the color buffer. And whatever gets written to the z channel of the output position register will be used as the depth value.
>
> Jose
>
> ________________________________________
> From: mesa-dev-bounces+jfonseca=vmware.com at lists.freedesktop.org [mesa-dev-bounces+jfonseca=vmware.com at lists.freedesktop.org] On Behalf Of Jose Fonseca [jfonseca at vmware.com]
> Sent: Thursday, September 30, 2010 7:28
> To: Dave Airlie; mesa-dev at lists.freedesktop.org
> Subject: Re: [Mesa-dev] depth writing and missing something
>
> There are two things to consider: u_format.csv description for depth stencils is a bit special for practical reasons, and pipe_sampler_view swizzles.
>
> Several functions in u_format_xxx.c need to be able to read/write stencil, and this is why u_format.csv describes depth stencil's swizzles as producing Z S x x. But the stencil channel will never be present when the texture is read as RGBA tuple.
>
> Sampling from a depthstencil texture should always produce Z Z Z 1 or Z 0 0 1, even before any sampler swizzles are applied. I think Brian documented this somewhere in gallium/docs/ but I can't find it now.
>
> At any rate, provided the first channel has z, then the state tracker will specify how he wants the other channels to be filled in the pipe_sampler_view' swizzles.
>
> Effectively, the gallium spec could say that sampling from depth textures should match (Z x x x).
>
> This is my understanding of the current state. We could polish this more a little.
>
> Jose
>
> ________________________________________
> From: mesa-dev-bounces+jfonseca=vmware.com at lists.freedesktop.org [mesa-dev-bounces+jfonseca=vmware.com at lists.freedesktop.org] On Behalf Of Dave Airlie [airlied at gmail.com]
> Sent: Thursday, September 30, 2010 2:34
> To: mesa-dev at lists.freedesktop.org
> Subject: [Mesa-dev] depth writing and missing something
>
> So I've been playing with stencil writing on r600, and it lead me to
> examine the depth writing.
>
> So at the moment in gallium if we are writing to depth via DrawPixels,
> we construct a fragment program that samples from a texture.
>
> TEX OUT[0].z, IN[1], SAMP[0], 2D
>
> Now from what I can see the format we pick to sample from is
> Z24_UNORM_S8_USCALED, which from the u_format.csv file seems to say it
> will put the results into X and Y components. Now if we sample from
> the X and Y components and the texture dest writemask is Z, I can't
> see how any value arrives in the right place. It seems to work but I'm
> a bit lost where the magic is.
>
> I'd have expected there to be swizzles in the sampler but I can't see
> them being set to anything special either.
>
> Dave.
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-- 
When the facts change, I change my mind. What do you do, sir? ~ Keynes

Corbin Simpson
<MostAwesomeDude at gmail.com>