[gimp] Bug 325564 – Use CIE LCH instead of HSL for layer mode "Color"

[Martin Nordholts <martinn src gnome org>]

commit 77e233f4c76cb4b6cf69b9b483a9fec8e27e8f37
Author: Martin Nordholts <martinn src gnome org>
Date:   Sun Aug 2 11:07:40 2009 +0200

    Bug 325564 â?? Use CIE LCH instead of HSL for layer mode "Color"
    
    When GEGL is used for the projection, use CIE LCH instead of HSL for
    the "Color" layer mode. This give much more accurate and intuitive
    results. Requires at least 12d5cc4c1bcfb of babl.

 app/gegl/gimpoperationpointlayermode.c |   67 ++++++++++++++++++--------------
 1 files changed, 38 insertions(+), 29 deletions(-)
---
diff --git a/app/gegl/gimpoperationpointlayermode.c b/app/gegl/gimpoperationpointlayermode.c
index 6ace466..8b2f5be 100644
--- a/app/gegl/gimpoperationpointlayermode.c
+++ b/app/gegl/gimpoperationpointlayermode.c
@@ -45,6 +45,9 @@
 #define G     (GREEN)
 #define B     (BLUE)
 #define A     (ALPHA)
+#define L     0
+#define C     1
+#define H     2
 #define inA   (in[A])
 #define inCa  (in[c])
 #define inC   (in[A]  ? in[c]  / in[A]  : 0.0)
@@ -243,40 +246,46 @@ gimp_operation_point_layer_mode_get_new_color_hsv (GimpLayerModeEffects  blend_m
 }
 
 static void
-gimp_operation_point_layer_mode_get_new_color_hsl (GimpLayerModeEffects  blend_mode,
-                                                   const gfloat         *in,
-                                                   const gfloat         *lay,
-                                                   gfloat               *new)
+gimp_operation_point_layer_mode_get_new_color_lchab (GimpLayerModeEffects  blend_mode,
+                                                     const gfloat         *in,
+                                                     const gfloat         *lay,
+                                                     gfloat               *new)
 {
-  GimpRGB inRGB;
-  GimpHSL inHSL;
-  GimpRGB layRGB;
-  GimpHSL layHSL;
-  GimpRGB newRGB;
-  GimpHSL newHSL;
+  float in_lchab[3];
+  float lay_lchab[3];
+  float new_lchab[3];
+  Babl *ragabaa_to_lchab = babl_fish (babl_format ("RaGaBaA float"),
+                                      babl_format ("CIE LCH(ab) float"));
+  Babl *lchab_to_ragabaa = babl_fish (babl_format ("CIE LCH(ab) float"),
+                                      babl_format ("RaGaBaA float"));
 
-  gimp_rgb_set (&inRGB,  in[R],  in[G],  in[B]);
-  gimp_rgb_set (&layRGB, lay[R], lay[G], lay[B]);
-
-  gimp_rgb_to_hsl (&inRGB,  &inHSL);
-  gimp_rgb_to_hsl (&layRGB, &layHSL);
+  babl_process (ragabaa_to_lchab, (void*)in,  (void*)in_lchab,  1);
+  babl_process (ragabaa_to_lchab, (void*)lay, (void*)lay_lchab, 1);
 
   switch (blend_mode)
     {
     case GIMP_HUE_MODE:
-      gimp_hsl_set (&newHSL, layHSL.h, inHSL.s,  inHSL.l);
+      new_lchab[L] = in_lchab[L];
+      new_lchab[C] = in_lchab[C];
+      new_lchab[H] = lay_lchab[H];
       break;
 
     case GIMP_SATURATION_MODE:
-      gimp_hsl_set (&newHSL, inHSL.h,  layHSL.s, inHSL.l);
+      new_lchab[L] = in_lchab[L];
+      new_lchab[C] = lay_lchab[C];
+      new_lchab[H] = in_lchab[H];
       break;
 
     case GIMP_COLOR_MODE:
-      gimp_hsl_set (&newHSL, layHSL.h, layHSL.s, inHSL.l);
+      new_lchab[L] = in_lchab[L];
+      new_lchab[C] = lay_lchab[C];
+      new_lchab[H] = lay_lchab[H];
       break;
 
-    case GIMP_VALUE_MODE:
-      gimp_hsl_set (&newHSL, inHSL.h,  inHSL.s,  layHSL.l);
+    case GIMP_VALUE_MODE: /* GIMP_LIGHTNESS_MODE */
+      new_lchab[L] = lay_lchab[L];
+      new_lchab[C] = in_lchab[C];
+      new_lchab[H] = in_lchab[H];
       break;
 
     default:
@@ -284,11 +293,7 @@ gimp_operation_point_layer_mode_get_new_color_hsl (GimpLayerModeEffects  blend_m
       break;
     }
 
-  gimp_hsl_to_rgb (&newHSL, &newRGB);
-
-  new[R] = newRGB.r;
-  new[G] = newRGB.g;
-  new[B] = newRGB.b;
+  babl_process (lchab_to_ragabaa, new_lchab, new, 1);
 }
 
 static void
@@ -601,10 +606,14 @@ gimp_operation_point_layer_mode_process (GeglOperation       *operation,
            *
            * f(Sc, Dc) = New color
            */
-          gimp_operation_point_layer_mode_get_new_color_hsl (blend_mode,
-                                                             in,
-                                                             lay,
-                                                             new);
+
+          /* FIXME: Doing this call for each pixel is very slow, we
+           * should make conversions on larger chunks of data
+           */
+          gimp_operation_point_layer_mode_get_new_color_lchab (blend_mode,
+                                                               in,
+                                                               lay,
+                                                               new);
           EACH_CHANNEL (
           outCa = newCa * layA * inA + layCa * (1 - inA) + inCa * (1 - layA));
           break;