[Mesa-dev] [PATCH 01/15] i965: get the proper vertex surface type for doubles on gen8+

[Kenneth Graunke]

On Wednesday, May 4, 2016 3:30:13 PM PDT Alejandro Piñeiro wrote:
> 
> On 04/05/16 12:31, Kenneth Graunke wrote:
> > On Thursday, April 28, 2016 1:40:31 PM PDT Antia Puentes wrote:
> >> From: Alejandro Piñeiro <apinheiro at igalia.com>
> >>
> >> This commit adds support for PASSTHRU format when pushing
> >> double-precision attributes.
> >>
> >> Check glarray->Doubles in order to know if we should choose a format
> >> that does a conversion to float, or just passthru the 64-bit double.
> >> ---
> >>  src/mesa/drivers/dri/i965/brw_draw_upload.c | 30 +++++++++++++++++++++++
++
> > +---
> >>  1 file changed, 27 insertions(+), 3 deletions(-)
> > What's the motivation for using the PASSTHRU formats?  Is there some
> > advantage over just using the R64*FLOAT formats?
> 
> We can't use R64*FLOAT because it does a double to float conversion, as
> explained at the bdw PRM (vol 7, section 10.15, page 470, Table "Source
> Element Formats Supported in VF Unit"). PASSTHRU ensures that the
> 64-bits are passed without any conversion, that is what we want. If it
> is not clear reading the commit message, I could expand it.

Ahh...thanks.  For some reason, I just assumed that R64_FLOAT meant
double precision float, not "reads a 64 bit float and outputs a 32 bit
float".  Heh :)

Thanks for the explanation!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: This is a digitally signed message part.
URL: <https://lists.freedesktop.org/archives/mesa-dev/attachments/20160504/9a2e5663/attachment.sig>