[Mesa-dev] [PATCH] glsl: always do sqrt(abs()) and inversesqrt(abs())

[Nicolai Hähnle]

On 11.01.2017 13:17, Marek Olšák wrote:
> On Tue, Jan 10, 2017 at 6:48 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>> I'll be honest, I'm not a fan... Given that D3D10 has one defined behavior,
>> D3D9 has another, and GL doesn't specify, I don't really think we should be
>> making a global change to all drivers to do the D3D9 behavior just to fix
>> one app.  Sure, other apps probably have the same bug, but are we going to
>> have apps that expect the D3D10 behavior that we've now explicitly made not
>> work?
>>
>> If we're going to hack around an app bug, I would really rather see it
>> behind a driconf option rather than a global change to driver behavior.
>> Even better, it'd be cool if we could see the app get fixed. (Yes, I know
>> that's not likely).
>
> I think we are not in a position to refuse this workaround, or put
> more precisely, to have a different behavior from everybody else. By
> "we", I mean i965, radeonsi, svga. All closed drivers use abs. Many
> Mesa drivers also use abs internally (r300, r600, nv30, nv50/nvc0).
> This is not really a workaround for a specific application, even
> though it's strongly motivated by that. It's a fix to align the few
> remaining drivers with all others.
>
> We talked with the publisher about this a very long time ago. While I
> don't remember the details (Nicolai?), I think they refused to fix it
> because radeonsi appeared to be the only driver not doing abs.

If I remember correctly, it wasn't so much a refusal as a lack of 
follow-through. They even had an option in their framework to add the 
abs(...) when translating shaders, but somehow didn't turn it on 
unconditionally for some reason...

Nicolai

>
> Marek
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