[Mesa-dev] [PATCH 4/5] gallium: Add PIPE_SHADER_CAP_DOUBLES

[Roland Scheidegger]

Am 18.06.2014 01:54, schrieb Dave Airlie:
> On 18 June 2014 05:08, Roland Scheidegger <sroland at vmware.com> wrote:
>> This looks ok to me though since tgsi currently doesn't have any double
>> opcodes (well the docs have them...) it doesn't really apply to most
>> drivers (at least I assume you don't want to add support for it for tgsi).
> 
> I've mostly forward ported the old gallium double code, and have
> written most of ARB_gpu_shader_fp64 on top,
> 
> Though the question I did want to ask Tom is if he is just going to
> expose hw that has doubles, or does
> he plan on emulating doubles.
> 
> For a lot of GLSL4.0 GPUs from AMD fglrx emulates doubles using
> massive magic shaders, I'm unsure
> if we should have a lowering pass above/below the TGSI line for these
> types of situations and what that
> would mean for this CAP.

Oh that's interesting. I always thought drivers didn't emulate that, and
if apps want doubles but the device doesn't provide them it needs to do
that itself. For which chips does fglrx do that?
If you'd want to emulate this, the other question is if you can do it at
the tgsi level, or if this was exploiting some hw specific bits (well of
course you could still do it at tgsi level, but if the hw has some bits
to make this easier, then this isn't efficient). In any case I guess
this could be decided later.

Roland