[Mesa-dev] [PATCH 2/3] mesa/st: add per sample shading state to fp key and set interpolation

[Marek Olšák]

There is this vague statement in the sample shading spec:

    When the sample shading fraction is 1.0, a separate set of colors and
    other associated data are evaluated for each sample, each set of values
    are evaluated at the sample location.

I thought it was about interpolation, meaning that the fraction must
1.0 for the per-sample interpolation to be enabled, right?

Marek


On Sat, Jul 5, 2014 at 6:07 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
> This enables a gallium driver not to care about the semantics of
> ARB_sample_shading vs ARB_gpu_shader5 sample attributes. When
> ARB_sample_shading-style sample shading is enabled, all of the fp inputs
> are marked for interpolation at the sample location.
>
> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
> ---
>
> I _think_ I got this right... at least the tests still pass. But my
> understanding of all the various update atoms, etc is really weak... please
> read carefully :)
>
> Now that I understand all this interpolation stuff better, I see why it was
> suggested I add proper per-sample interpolation first and the
> ARB_sample_shading stuff second. Oh well...
>
>  src/mesa/state_tracker/st_atom_shader.c | 6 +++++-
>  src/mesa/state_tracker/st_program.c     | 3 +++
>  src/mesa/state_tracker/st_program.h     | 3 +++
>  3 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/src/mesa/state_tracker/st_atom_shader.c b/src/mesa/state_tracker/st_atom_shader.c
> index 67c6157..6515a98 100644
> --- a/src/mesa/state_tracker/st_atom_shader.c
> +++ b/src/mesa/state_tracker/st_atom_shader.c
> @@ -89,6 +89,10 @@ update_fp( struct st_context *st )
>     key.clamp_color = st->clamp_frag_color_in_shader &&
>                       st->ctx->Color._ClampFragmentColor;
>
> +   /* Ignore sample qualifier while computing this flag. */
> +   key.persample_shading =
> +      _mesa_get_min_invocations_per_fragment(st->ctx, &stfp->Base, true) > 1;
> +
>     st->fp_variant = st_get_fp_variant(st, stfp, &key);
>
>     st_reference_fragprog(st, &st->fp, stfp);
> @@ -108,7 +112,7 @@ update_fp( struct st_context *st )
>  const struct st_tracked_state st_update_fp = {
>     "st_update_fp",                                     /* name */
>     {                                                   /* dirty */
> -      _NEW_BUFFERS,                                    /* mesa */
> +      _NEW_BUFFERS | _NEW_MULTISAMPLE,                 /* mesa */
>        ST_NEW_FRAGMENT_PROGRAM                           /* st */
>     },
>     update_fp                                   /* update */
> diff --git a/src/mesa/state_tracker/st_program.c b/src/mesa/state_tracker/st_program.c
> index b603759..9d7b7c4 100644
> --- a/src/mesa/state_tracker/st_program.c
> +++ b/src/mesa/state_tracker/st_program.c
> @@ -548,6 +548,9 @@ st_translate_fragment_program(struct st_context *st,
>           else
>              interpLocation[slot] = TGSI_INTERPOLATE_LOC_CENTER;
>
> +         if (key->persample_shading)
> +            interpLocation[slot] = TGSI_INTERPOLATE_LOC_SAMPLE;
> +
>           switch (attr) {
>           case VARYING_SLOT_POS:
>              input_semantic_name[slot] = TGSI_SEMANTIC_POSITION;
> diff --git a/src/mesa/state_tracker/st_program.h b/src/mesa/state_tracker/st_program.h
> index ce9174f..9a5b6a8 100644
> --- a/src/mesa/state_tracker/st_program.h
> +++ b/src/mesa/state_tracker/st_program.h
> @@ -58,6 +58,9 @@ struct st_fp_variant_key
>
>     /** for ARB_color_buffer_float */
>     GLuint clamp_color:1;
> +
> +   /** for ARB_sample_shading */
> +   GLuint persample_shading:1;
>  };
>
>
> --
> 1.8.5.5
>
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