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

Sun, 04 Mar 2018 05:37:13 -0800

On March 4, 2018 01:57:33 "Pohjolainen, Topi" <[email protected]> wrote: 


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).


I have no recollection whatsoever why I chose that one.


Reviewed-by: Topi Pohjolainen <[email protected]>




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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