Re: [RFC PATCH 00/11] Implement ARB_cull_distance

[Tobias Klausmann <tobias.johannes.klausmann-AqjdNwhu20eELgA04lAiVw@public.gmane.org>]

On 25.05.2015 17:07, Ilia Mirkin wrote:
> On Mon, May 25, 2015 at 9:40 AM, Tobias Klausmann
> <tobias.johannes.klausmann@mni.thm.de> wrote:
>> On 25.05.2015 07:17, Dave Airlie wrote:
>>> On 25 May 2015 at 08:11, Marek Olšák <maraeo@gmail.com> wrote:
>>>> It's the same on Radeon. There are 2x ClipOrCullDistance output
>>>> vectors and a mask saying it should clip or cull or do nothing.
>>>>
>>>> Marek
>>>>
>>> My thinking was gallium should have a single semantic and a mask in
>>> the shader definition maybe.
>>>
>>> though it doesn't solve the does nvidia do the right thing with
>>> cull[0] and clip[0], and what is the right thing.
>>>
>>> Dave.
>>
>> I'm still convinced that both clip[0] and cull[0] should be possible. Plus i
>> have written a shader_test for this a while ago which you pushed to piglit
>> (fs-cull-and-clip-distance-different.shader_test). If i remember right
>> nvidia passed that test just fine.
> My take (and note that I last read the extension many months ago) is
> that you're supposed to figure out the max gl_ClipDistance[] written,
> and then write all your cull distances above that. So if you, e.g.,
> have something like
>
> gl_ClipDistance[5] = 1;
> gl_CullDistance[0] = 1;
>
> Then it would decide that there are 6 clip distances (or if there's an
> explicit out float gl_ClipDistance[n], then use that), and 1 cull
> distance. In the TGSI, I'm thinking this might look approximately like
>
> PROPERTY CULL_MASK (1<<6)
> DCL OUT[0], CLIPDIST[0]
> DCL OUT[1], CLIPDIST[1]
> MOV OUT[1].y, 1 (clip distance[5])
> MOV OUT[1].z, 1 (cull distance[0])
>
> Then basically you'd have
>
> (rast->clip_enable & shader->actual_clip_writes_mask) | cull_mask =
> the enabled distances
> cull_mask = cull mask
>
> This would work *very* well for nouveau, not sure how suitable it is
> for other hardware.
>
> Cheers,
>
>    -ilia
I wonder where this step should be implemented after all. It was brought 
up that llvmpipe already supports cull_distance (it does!), so maybe we 
should implement this in the drivers to evade llvmpipe breakage. Any 
suggestions appreciated :)

Tobias
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