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

[Marek Olšák]

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.

Marek