[Mesa-dev] [PATCH 08/29] nir/format_convert: Add linear <-> sRGB helpers

[Pohjolainen, Topi]

On Fri, Jan 26, 2018 at 05:59:37PM -0800, Jason Ekstrand wrote:
> ---
>  src/compiler/nir/nir_format_convert.h | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)

I don't what is the official reference for the formulas and I just took what
google gave me first. There was discussion about the cutoff point between
linear and curved. I got the impression that what you chose below
(open-ended: 0 <= linear < 0.0031308f and 0 <= linear < 0.04045f instead of
close-ended) was more "correct". Just thought I check that anyway (that you
chose that on purpose).

Reviewed-by: Topi Pohjolainen <topi.pohjolainen at intel.com>

> 
> diff --git a/src/compiler/nir/nir_format_convert.h b/src/compiler/nir/nir_format_convert.h
> index e09c955..07618dc 100644
> --- a/src/compiler/nir/nir_format_convert.h
> +++ b/src/compiler/nir/nir_format_convert.h
> @@ -104,3 +104,29 @@ nir_format_pack_uint(nir_builder *b, nir_ssa_def *color,
>     return nir_format_pack_uint_unmasked(b, nir_iand(b, color, mask_imm),
>                                          bits, num_components);
>  }
> +
> +static inline nir_ssa_def *
> +nir_format_linear_to_srgb(nir_builder *b, nir_ssa_def *c)
> +{
> +   nir_ssa_def *linear = nir_fmul(b, c, nir_imm_float(b, 12.92f));
> +   nir_ssa_def *curved =
> +      nir_fsub(b, nir_fmul(b, nir_imm_float(b, 1.055f),
> +                              nir_fpow(b, c, nir_imm_float(b, 1.0 / 2.4))),
> +                  nir_imm_float(b, 0.055f));
> +
> +   return nir_fsat(b, nir_bcsel(b, nir_flt(b, c, nir_imm_float(b, 0.0031308f)),
> +                                   linear, curved));
> +}
> +
> +static inline nir_ssa_def *
> +nir_format_srgb_to_linear(nir_builder *b, nir_ssa_def *c)
> +{
> +   nir_ssa_def *linear = nir_fdiv(b, c, nir_imm_float(b, 12.92f));
> +   nir_ssa_def *curved =
> +      nir_fpow(b, nir_fdiv(b, nir_fadd(b, c, nir_imm_float(b, 0.055f)),
> +                              nir_imm_float(b, 1.055f)),
> +                  nir_imm_float(b, 2.4f));
> +
> +   return nir_fsat(b, nir_bcsel(b, nir_flt(b, c, nir_imm_float(b, 0.04045f)),
> +                                   linear, curved));
> +}
> -- 
> 2.5.0.400.gff86faf
> 
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