[Mesa-dev] RFC: mesa/st dynamic sampler support in tgsi

[Ilia Mirkin]

*needed*? No, I can't. However without changing a bunch of stuff
around, doing something like

TEX TEMP[ADDR[0].x], SAMP[reladdr], coord, etc

Is going to be tricky. It'd be a little dangerous to use ADDR[1] there
since it's meant to be the dimension, and you could easily have, with
tessellation,

TEX OUT[ADDR[1].x][ADDR[0].x], SAMP[reladdr], ...

Now I could obviously rewrite that as

TEX TEMP[foo], SAMP[ADDR[0].x], ...
UARL ADDR[0]
UARL ADDR[1]
MOV OUT[ADDR[1].x][ADDR[0].x], TEMP[foo]

But then I'd have to somehow communicate the emit() that it needs to
arrange for this. Not impossible, but tricky.

  -ilia

On Tue, Aug 5, 2014 at 4:04 PM, Marek Olšák <maraeo at gmail.com> wrote:
> Could you please show us an example in TGSI where a 3rd address
> register is needed?
>
> Thanks,
>
> Marek
>
> On Tue, Aug 5, 2014 at 6:54 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> Hello,
>>
>> I'm in the process of working out the details of adding dynamic
>> sampler support to mesa/st as part of ARB_gpu_shader5. Unfortunately
>> I've run into a bit of a roadblock.
>>
>> One approach I've tried is to load the indirect sampler index into an
>> address register and then use that as the offset. However in order to
>> realistically support that I need a 3rd address register, while right
>> now tgsi_ureg limits it to 2 address registers. Would it be OK to
>> relax the restriction to 3? (The reason I need a third is that if e.g.
>> the dst has a reladdr, I'd have to change a bunch of stuff to make
>> that function properly without a 3rd addr reg, since I can't just MOV
>> the sampler to a temp like it does for all the other src's.)
>>
>> Another apporach I've tried is to just use a TEMP register as the
>> indirect offset here. Unfortunately this gets destroyed by
>> st_glsl_to_tgsi's various optimizations which assume that temp
>> registers can't be reladdr's and so messes up the values. I started
>> adding support for that, but then quickly realized that was probably
>> not the right thing to do.
>>
>> So... should I increase the number of address registers to 1? Or is
>> there some other simple approach that I'm missing?
>>
>> Thanks,
>>
>>   -ilia
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