[Mesa-dev] [PATCH 3/7] gallium: add FBFETCH opcode to retrieve the current sample value

[Erik Faye-Lund]

Ah, right. Thanks for the explanation!

On Jan 4, 2017 14:02, "Ilia Mirkin" <imirkin at alum.mit.edu> wrote:

> On Wed, Jan 4, 2017 at 4:24 AM, Erik Faye-Lund <kusmabite at gmail.com>
> wrote:
> > On Jan 2, 2017 06:03, "Ilia Mirkin" <imirkin at alum.mit.edu> wrote:
> >
> > Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
> > ---
> >  src/gallium/auxiliary/tgsi/tgsi_info.c     |  2 +-
> >  src/gallium/docs/source/tgsi.rst           | 11 +++++++++++
> >  src/gallium/include/pipe/p_shader_tokens.h |  2 +-
> >  3 files changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/gallium/auxiliary/tgsi/tgsi_info.c
> > b/src/gallium/auxiliary/tgsi/tgsi_info.c
> > index 37549aa..e34b8c7 100644
> > --- a/src/gallium/auxiliary/tgsi/tgsi_info.c
> > +++ b/src/gallium/auxiliary/tgsi/tgsi_info.c
> > @@ -106,7 +106,7 @@ static const struct tgsi_opcode_info
> > opcode_info[TGSI_OPCODE_LAST] =
> >     { 1, 3, 0, 0, 0, 0, 0, COMP, "CMP", TGSI_OPCODE_CMP },
> >     { 1, 1, 0, 0, 0, 0, 0, CHAN, "SCS", TGSI_OPCODE_SCS },
> >     { 1, 2, 1, 0, 0, 0, 0, OTHR, "TXB", TGSI_OPCODE_TXB },
> > -   { 0, 1, 0, 0, 0, 0, 1, NONE, "", 69 },      /* removed */
> > +   { 1, 1, 0, 0, 0, 0, 0, OTHR, "FBFETCH", TGSI_OPCODE_FBFETCH },
> >     { 1, 2, 0, 0, 0, 0, 0, COMP, "DIV", TGSI_OPCODE_DIV },
> >     { 1, 2, 0, 0, 0, 0, 0, REPL, "DP2", TGSI_OPCODE_DP2 },
> >     { 1, 2, 1, 0, 0, 0, 0, OTHR, "TXL", TGSI_OPCODE_TXL },
> > diff --git a/src/gallium/docs/source/tgsi.rst
> > b/src/gallium/docs/source/tgsi.rst
> > index d2d30b4..accbe1d 100644
> > --- a/src/gallium/docs/source/tgsi.rst
> > +++ b/src/gallium/docs/source/tgsi.rst
> > @@ -2561,6 +2561,17 @@ Resource Access Opcodes
> >    image, while .w will contain the number of samples for multi-sampled
> >    images.
> >
> > +.. opcode:: FBFETCH - Load data from framebuffer
> > +
> > +  Syntax: ``FBFETCH dst, output``
> > +
> > +  Example: ``FBFETCH TEMP[0], OUT[0]``
> > +
> > +  Returns the color of the current position in the framebuffer from
> > +  before this fragment shader invocation. Always returns the same
> > +  value from multiple calls for a particular output within a single
> > +  invocation.
> > +
> >
> >
> > What does this instruction do under MRT? Tegra (AR20) has the ability to
> > select the MRT index...
>
> Fetches the relevant output's value. Just as with the new sysval-based
> implementation,
>
> DECL SV[0], COLOR[1]
>
> would fetch the value in RT1. This could be used to implement
> EXT_shader_framebuffer_fetch, although more cap's would be necessary
> to differentiate the use-cases.
>
> Cheers,
>
>   -ilia
>
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