[Mesa-dev] [PATCH 0/8] gl_FragCoord and gl_FrontFacing as system values

[Rob Clark]

On Fri, Jan 8, 2016 at 5:59 PM, Ian Romanick <idr at freedesktop.org> wrote:
> On 01/08/2016 07:39 AM, Brian Paul wrote:
>> On 01/07/2016 06:29 PM, Marek Olšák wrote:
>>> Hi,
>>>
>>> This series adds the possibility for drivers to get gl_FragCoord and
>>> gl_FrontFacing as system values. When FACE is a system value, it also
>>> changes its type to integer from floating-point.
>>>
>>> Each variable has its own Const flag / Gallium CAP, so drivers can
>>> choose whether they want this for each variable.
>>>
>>> This simplifies input handling in the radeonsi driver. With this, TGSI
>>> INPUT[i] becomes fragment shader input[i] in the hardware, so the
>>> driver doesn't have to do any translation of locations.
>>>
>>> Please review.
>>
>> Looks good overall.  I probably should have made fragcoord and
>> frontfacing system values from day one.  We could probably migrate all
>> the drivers to that convention over time.
>
> We can probably migrate frontfacing, but I don't think we can / should
> for fragcoord.  On some hardware it's not a system value, and that
> changes how we have to count the resource usage.

although if hw treats it as a normal input, it is easier to append an
input at the end, than reshuffle to remove an input..

at any rate, at least for frontface, I think this would make it
slightly easier for tgsi_to_nir to spit out NIR that is more similar
to glsl_to_nir..  I don't remember, maybe I had to fixup fragcoord too
on my mesa/st glsl_to_nir branch..

BR,
-R

>> Clarification about the integer front/back face values would be good.
>>
>> Reviewed-by: Brian Paul <brianp at vmware.com>
>>
>> -Brian
>>
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