[babl] babl: handle 7 parameter ICC v4 TRCs

[Øyvind "pippin" Kolås <ok src gnome org>]

commit b61af1caa1b7f0282ade13493e6a517c112934ec
Author: Øyvind Kolås <pippin gimp org>
Date:   Fri Aug 7 21:59:36 2020 +0200

    babl: handle 7 parameter ICC v4 TRCs

 babl/babl-icc.c      | 21 ++++++++-------------
 babl/babl-internal.h |  2 +-
 babl/babl-trc.c      | 28 +++++++++++++++++++---------
 3 files changed, 28 insertions(+), 23 deletions(-)
---
diff --git a/babl/babl-icc.c b/babl/babl-icc.c
index a21888f70..aa5a3862d 100644
--- a/babl/babl-icc.c
+++ b/babl/babl-icc.c
@@ -386,16 +386,16 @@ babl_trc_from_icc (ICC         *state,
               break;
             case 3:
               {
-                float a,b,c,d;
+                float a,b,c,d, e, f;
                 g = icc_read (s15f16, offset + 12 + 4 * 0);
                 a = icc_read (s15f16, offset + 12 + 4 * 1);
                 b = icc_read (s15f16, offset + 12 + 4 * 2);
                 c = icc_read (s15f16, offset + 12 + 4 * 3);
                 d = icc_read (s15f16, offset + 12 + 4 * 4);
-                //fprintf (stderr, "%f %f %f %f %f\n", g, a, b, c, d);
-                return babl_trc_formula_srgb (g, a, b, c, d);
+                e = 0.0f;
+                f = 0.0f;
+                return babl_trc_formula_srgb (g, a, b, c, d, e, f);
               }
-              break;
             case 4:
               {
                 float a,b,c,d,e,f;
@@ -406,15 +406,10 @@ babl_trc_from_icc (ICC         *state,
                 d = icc_read (s15f16, offset + 12 + 4 * 4);
                 e = icc_read (s15f16, offset + 12 + 4 * 5);
                 f = icc_read (s15f16, offset + 12 + 4 * 6);
-                fprintf (stderr, "%f %f %f %f %f %f %f\n",
-                              g, a, b, c, d, e, f);
-            {
-              fprintf (stderr, "unhandled parametric sRGB formula TRC type %i\n", function_type);
-              *error = "unhandled sRGB formula like TRC";
-              return babl_trc_gamma (2.2);
-            }
-                              }
-              break;
+                return babl_trc_formula_srgb (g, a, b, c, d, e, f);
+              }
+            case 1: // NYI
+            case 2: // NYI - can share code, like srgb formulas
             default:
               *error = "unhandled parametric TRC";
               fprintf (stderr, "unhandled parametric TRC type %i\n", function_type);
diff --git a/babl/babl-internal.h b/babl/babl-internal.h
index b3c97854f..1efdb0f2f 100644
--- a/babl/babl-internal.h
+++ b/babl/babl-internal.h
@@ -385,7 +385,7 @@ babl_conversion_create_name (Babl *source, Babl *destination, int type,
 
 void _babl_space_add_universal_rgb (const Babl *space);
 const Babl *
-babl_trc_formula_srgb (double gamma, double a, double b, double c, double d);
+babl_trc_formula_srgb (double gamma, double a, double b, double c, double d, double e, double f);
 
 
 const Babl *babl_space_match_trc_matrix (const Babl *trc_red,
diff --git a/babl/babl-trc.c b/babl/babl-trc.c
index e76bb9201..cfb31b1c3 100644
--- a/babl/babl-trc.c
+++ b/babl/babl-trc.c
@@ -165,16 +165,19 @@ _babl_trc_formula_srgb_from_linear (const Babl *trc_,
   float b = trc->lut[2];
   float c = trc->lut[3];
   float d = trc->lut[4];
-  if (x > c * d)  // XXX: verify that this math is the correct inverse
+  float e = trc->lut[5];
+  float f = trc->lut[6];
+
+  if (x - f > c * d)  // XXX: verify that this math is the correct inverse
   {
-    float v = _babl_trc_gamma_from_linear ((Babl *) trc, x);
+    float v = _babl_trc_gamma_from_linear ((Babl *) trc, x - f);
     v = (v-b)/a;
     if (v < 0.0 || v >= 0.0)
       return v;
     return 0.0;
   }
   if (c > 0.0)
-    return x / c;
+    return (x - e) / c;
   return 0.0;
 }
 
@@ -188,12 +191,14 @@ _babl_trc_formula_srgb_to_linear (const Babl *trc_,
   float b = trc->lut[2];
   float c = trc->lut[3];
   float d = trc->lut[4];
+  float e = trc->lut[5];
+  float f = trc->lut[6];
 
   if (x >= d)
   {
-    return _babl_trc_gamma_to_linear ((Babl *) trc, a * x + b);
+    return _babl_trc_gamma_to_linear ((Babl *) trc, a * x + b) + e;
   }
-  return c * x;
+  return c * x + f;
 }
 
 static inline float 
@@ -479,20 +484,25 @@ babl_trc_formula_srgb (double g,
                        double a, 
                        double b, 
                        double c, 
-                       double d)
+                       double d,
+                       double e,
+                       double f)
 {
   char name[128];
   int i;
-  float params[5]={g, a, b, c, d};
+  float params[7]={g, a, b, c, d, e, f};
 
   if (fabs (g - 2.400) < 0.01 &&
       fabs (a - 0.947) < 0.01 &&
       fabs (b - 0.052) < 0.01 &&
       fabs (c - 0.077) < 0.01 &&
-      fabs (d - 0.040) < 0.01)
+      fabs (d - 0.040) < 0.01 &&
+      fabs (e - 0.000) < 0.01 &&
+      fabs (f - 0.000) < 0.01
+      )
     return babl_trc ("sRGB");
 
-  snprintf (name, sizeof (name), "%.6f %.6f %.4f %.4f %.4f", g, a, b, c, d);
+  snprintf (name, sizeof (name), "%.6f %.6f %.4f %.4f %.4f %.4f %.4f", g, a, b, c, d, e, f);
   for (i = 0; name[i]; i++)
     if (name[i] == ',') name[i] = '.';
   while (name[strlen(name)-1]=='0')