[Mesa-dev] Thoughts on fp64 for GLES?

[Elie Tournier]

On Fri, Jan 25, 2019 at 11:52:56AM -0800, Stéphane Marchesin wrote:
> On Fri, Jan 25, 2019 at 2:25 AM Gert Wollny <gw.fossdev at gmail.com> wrote:
> >
> > Am Donnerstag, den 24.01.2019, 22:25 -0800 schrieb Stéphane Marchesin:
> > >
> > > Yes, it's for running virgl on top of GLES. To emulate fp64 in GL on
> > > the guest side, we need fp64 on the host...
> >
> > BTW: we could also get it emulated from the guest side. When Elie (in
> > CC)  initially proposed the fp64 emulation series it was for r600 and
> > TGSI was emitted. The created shaders are horribly long and it is
> > certainly not performant, but if it's just for getting OpenGL 4.0
> > exposed it should be good enough.
> 
> Yes, Ilia suggested this on IRC yesterday. My impression is that not
> many applications/games need high performance fp64 (it's likely mostly
> compute stuff, which is not our target). I could be wrong though. If
> anyone knows differently, please tell us :)
> 
> >
> > I'm not sure though how much work it would be to add this to the soft
> > fp64 as it has now landed for NIR, though.
> 
> Yes, with virgl not using NIR, I am not sure how much work soft fp64
> will require.

I spent a bit of time on the project recently.
My thinking so far:
* FP64 is bad . But everyone knows that. :)
* Using the current soft fp64 require to emulate int64.
* Soft fp64 and int64 involve function call which is, iiuc, not really
supported in TGSI.
* Soft fp64 is tied to NIR. Some pass/hack need to be port to GLSLIR.

So the project will require a lot of work.

Elie

> 
> Stéphane
> 
> 
> >
> > Best,
> > Gert
> >