[Mesa-dev] [PATCH 2/3] nir/lower-tex: add srgb->linear lowering

[Jason Ekstrand]

On Tue, Apr 19, 2016 at 6:58 AM, Rob Clark <robdclark at gmail.com> wrote:

> From: Rob Clark <robclark at freedesktop.org>
>
> Signed-off-by: Rob Clark <robclark at freedesktop.org>
> ---
>  src/compiler/nir/nir.h           |  7 ++++++
>  src/compiler/nir/nir_lower_tex.c | 46
> ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 53 insertions(+)
>
> diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
> index bbbc208..2c0f705 100644
> --- a/src/compiler/nir/nir.h
> +++ b/src/compiler/nir/nir.h
> @@ -2301,6 +2301,13 @@ typedef struct nir_lower_tex_options {
>      * while 4 and 5 represent 0 and 1 respectively.
>      */
>     uint8_t swizzles[32][4];
> +
> +   /**
> +    * Bitmap of textures that need srgb to linear conversion.  If
> +    * (srgb_to_linear & (1 << texture_index)) then the rgb (xyz)
> +    * components of the texture are lowered to linear.
> +    */
> +   unsigned lower_srgb;
>

You have lower_srgb here and srgb_to_linear in the comment.  Please pick
one.  I think I prefer srgb_to_linear as it's more explicit.


>  } nir_lower_tex_options;
>
>  bool nir_lower_tex(nir_shader *shader,
> diff --git a/src/compiler/nir/nir_lower_tex.c
> b/src/compiler/nir/nir_lower_tex.c
> index 7740e58..6bae3b7 100644
> --- a/src/compiler/nir/nir_lower_tex.c
> +++ b/src/compiler/nir/nir_lower_tex.c
> @@ -275,6 +275,45 @@ swizzle_result(nir_builder *b, nir_tex_instr *tex,
> const uint8_t swizzle[4])
>                                    swizzled->parent_instr);
>  }
>
> +static void
> +linearize_srgb_result(nir_builder *b, nir_tex_instr *tex)
> +{
> +   assert(tex->dest.is_ssa);
> +   assert(nir_tex_instr_dest_size(tex) == 4);
> +   assert(nir_alu_type_get_base_type(tex->dest_type) == nir_type_float);
> +
> +   b->cursor = nir_after_instr(&tex->instr);
> +
> +   nir_ssa_def *components[4];
> +
> +   /* first three channels are rgb: */
> +   for (unsigned i = 0; i < 3; i++) {
>

Um... NIR is a vector IR.  Why are we looping over channels?  Just do a
nir_swizzle to pick off the first three, do the sRGB conversion, and
nir_vec them back together with the alpha channel.


> +      /* Formula is:
> +       *    (comp <= 0.04045) ?
> +       *          (comp / 12.92) :
> +       *          pow((comp + 0.055) / 1.055, 2.4)
> +       */
> +      nir_ssa_def *comp = nir_channel(b, &tex->dest.ssa, i);
> +      nir_ssa_def *low  = nir_fmul(b, comp, nir_imm_float(b, 1.0 /
> 12.92));
>
+      nir_ssa_def *high = nir_fpow(b,
> +                                   nir_fmul(b,
> +                                            nir_fadd(b,
> +                                                     comp,
> +                                                     nir_imm_float(b,
> 0.055)),
> +                                            nir_imm_float(b, 1.0 /
> 1.055)),
> +                                   nir_imm_float(b, 2.4));
> +      nir_ssa_def *cond = nir_fge(b, nir_imm_float(b, 0.04045), comp);
> +      components[i] = nir_bcsel(b, cond, low, high);
> +   }
> +
> +   /* alpha is untouched: */
> +   components[3] = nir_channel(b, &tex->dest.ssa, 3);
> +
> +   nir_ssa_def *linearized = nir_vec(b, components, 4);
> +   nir_ssa_def_rewrite_uses_after(&tex->dest.ssa,
> nir_src_for_ssa(linearized),
> +                                  linearized->parent_instr);
> +}
> +
>  static bool
>  nir_lower_tex_block(nir_block *block, void *void_state)
>  {
> @@ -323,6 +362,13 @@ nir_lower_tex_block(nir_block *block, void
> *void_state)
>           swizzle_result(b, tex, options->swizzles[tex->texture_index]);
>           state->progress = true;
>        }
> +
> +      /* should be after swizzle so we know which channels are rgb: */
> +      if (((1 << tex->texture_index) & options->lower_srgb) &&
> +          !nir_tex_instr_is_query(tex) && !tex->is_shadow) {
> +         linearize_srgb_result(b, tex);
> +         state->progress = true;
> +      }
>     }
>
>     return true;
> --
> 2.5.5
>
>
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