[Mesa-dev] [PATCH v3 06/29] glsl: add ARB_gpu_shader_fp64 to the glsl extensions. (v2)

[Dave Airlie]

On 9 February 2015 at 09:30, Matt Turner <mattst88 at gmail.com> wrote:
> On Sun, Feb 8, 2015 at 2:51 PM, Dave Airlie <airlied at gmail.com> wrote:
>> On 9 February 2015 at 08:44, Aditya Avinash <adityaavinash1 at gmail.com> wrote:
>>> Ya. I just want to know that part "only some r600".
>>> I believe some of the nv0 cards doesn't support double. You have any ideas
>>> or suggestions to make it possible?
>>
>> For AMD
>> http://en.wikipedia.org/wiki/List_of_AMD_graphics_processing_units
>>
>> has what cards directly support double precision for r600/700/evergreen
>>
>> The plan is to implement a soffloat library like the fglrx drivers do for the
>> GPUs that don't do doubles just to satisfy the GL4.0 requirement.
>
> i965 hardware needs varying degrees of help to do doubles (the
> round-down instruction doesn't work on doubles, for instance), so
> we'll need some amount of this.
>
> But I'm curious about what you think the cost:benefit is to writing
> what sounds like a potentially significant amount of code [1] to
> support doubles on old cards? For a feature that no one seems to use,
> no less.
>
> Actually, looking at the link you gave, Wikipedia says they just
> support GL 3.3. Does fglrx expose ARB_gpu_shader_fp64 but not GL 4.0
> on them?

fglrx exposes GL4.0 on all evergreen and later cards, since they support
ever other feature. Only Khronos could be stupid enough to have a spec
which allows for optional features via extension mechanisms then mandate
those features even though most GPUs from one of the manufacturers
couldn't support them, and the competing spec made them optional.

On r600/700 the issue is less of a problem.

Dave.