[Mesa-dev] [PATCH 4/5] gallium/u_blitter: use TXF if possible

[Marek Olšák]

On Wed, May 31, 2017 at 12:59 AM, Roland Scheidegger <sroland at vmware.com> wrote:
> Am 31.05.2017 um 00:46 schrieb Marek Olšák:
>> From: Marek Olšák <marek.olsak at amd.com>
>>
>> This fixes piglit:
>>     arb_texture_view-rendering-r32ui
>>
>> TEX (image_sample) flushes denorms to 0 with FP32 textures on GCN, but such
>> a texture can contain integer data written using an integer render view.
>> If we do a transfer blit with TEX, denorms are flushed to 0. Luckily,
>> TXF (image_load) doesn't do that.
>>
>> TXF also doesn't need to load the sampler state, so blit shaders don't have
>> to do s_load_dwordx4.
>>
>> TXF doesn't do CLAMP_TO_EDGE, so it can only be used if the src box is
>> in bounds, or if we clamp manually (this commit doesn't).
>
> Not that I think using TXF isn't a good idea, but shouldn't you make
> sure you end up with a blit which is guaranteed to preserve all bits
> here by using an appropriate format in the first place?
> That TXF isn't going to denorm flush with f32 formats merely sounds like
> an implementation detail of radeonsi to me, but I wouldn't say you could
> really count on it here for the blitter.

That's true. Sadly, radeonsi can't change the format here due to
a possible negative performance impact.

Marek