[Mesa-dev] [PATCH 30/30] mesa/st: require linear interpolation for ARB_texture_float

[Marek Olšák]

I meant Wine games and games ported from DX9 to GL, and all GL games
designed for DX9-level hardware.

I suggest you simply ignore what the specs are saying. GL was a mess at
that time and didn't match what the hardware was capable of. GL and
extensions started being reasonably defined for hardware with GL 3.0 /
DX10-level functionality.

Marek

On Tue, Nov 20, 2018 at 4:57 AM Erik Faye-Lund <erik.faye-lund at collabora.com>
wrote:

> On Tue, 2018-11-20 at 10:08 +0100, Erik Faye-Lund wrote:
> > On Tue, 2018-11-20 at 01:21 -0500, Marek Olšák wrote:
> > > I'd like to keep ARB_texture_float enabled on drivers that don't
> > > support linear interpolation. ARB_texture_float is required by DX9,
> > > which doesn't require linear interpolation.
> >
> > This logic sounds circular. Since ARB_texture_float *does* require
> > linear interpolation, are you sure DX9 requires ARB_texture_float?
> > How
> > would DirectX even require a GL extension?
> >
> > Are you talking about Gallium Nine or something like that? If so, it
> > should probably require some combination of OES_texture_half_float
> > and
> > OES_texture_float instead, no?
> >
> > FWIW, I can't find any refreences to ARB_texture_float in Gallium
> > Nine...
> >
> > What exactly are you talking about?
> >
>
> OK, I think perhaps I've figured it out; you're probably referring to
> Wine's emulation. And the problem is that OES_texture_half_float /
> OES_texture_float are only available (outside of mesa) from OpenGL ES.
> A state-tracker has enough information, but not an application.
>
> It looks a bit to me like there's simply no OpenGL extension that
> matches the DX9 behavior. I find this surprising, because ATI had a
> bunch of floating-point texturing demos for Radeon 9600 etc. Even
> ATI_texture_float doesn't seem to diallow filtering either...
>
> This also brings up another problem. We expose ATI_texture_float if
> ARB_texture_float is supported. But this seems like a bad choice;
> ATI_texture_float defines a *different* 16-bit floating point format
> than ARB_texture_float. From the ATI_texture_float spec:
>
> "There are no NAN or infinity values for 16 bit floating-point."
>
> However, the ARB_texture_float-extension defines both NAN and infinity
> values...
>
> Especially NAN-propagation has been problematic with cross-API
> emulation in the past.
>
> Since the ATI_texture_float and ARB_texture_float enums have the same
> values, I doubt there's little to do here apart from either accepting
> this problem, or stop advertising ATI_texture_float (which probably
> leads to problems with old applications that doesn't care about NAN /
> infinity)...
>
> But perhaps we should at least document problems like these somewhere?
>
>
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