[gnome-photos] operation-saturation: Use CIE Lab for anything that is not CIE LCH(ab)

[Debarshi Ray <debarshir src gnome org>]

commit f5c8173669c71d4b7a3a739efdb53c2e8e06bdb7
Author: Debarshi Ray <debarshir gnome org>
Date:   Mon Jan 11 11:16:10 2016 +0100

    operation-saturation: Use CIE Lab for anything that is not CIE LCH(ab)
    
    The cost of converting from the RGB colour space to CIE LCH(ab) is much
    higher than the savings from one less floating point multiplication.
    
    This keeps the code in sync with gegl.

 src/photos-operation-saturation.c |   81 +++++++++++++++++++++++++++++++++++--
 1 files changed, 77 insertions(+), 4 deletions(-)
---
diff --git a/src/photos-operation-saturation.c b/src/photos-operation-saturation.c
index e882138..78ceb34 100644
--- a/src/photos-operation-saturation.c
+++ b/src/photos-operation-saturation.c
@@ -53,6 +53,57 @@ G_DEFINE_TYPE (PhotosOperationSaturation, photos_operation_saturation, GEGL_TYPE
 
 
 static void
+photos_operation_saturation_process_lab (GeglOperation *operation,
+                                         void *in_buf,
+                                         void *out_buf,
+                                         glong n_pixels,
+                                         const GeglRectangle *roi,
+                                         gint level)
+{
+  PhotosOperationSaturation *self = PHOTOS_OPERATION_SATURATION (operation);
+  gfloat *in = in_buf;
+  gfloat *out = out_buf;
+  glong i;
+
+  for (i = 0; i < n_pixels; i++)
+    {
+      out[0] = in[0];
+      out[1] = in[1] * self->scale;
+      out[2] = in[2] * self->scale;
+
+      in += 3;
+      out += 3;
+    }
+}
+
+
+static void
+photos_operation_saturation_process_lab_alpha (GeglOperation *operation,
+                                               void *in_buf,
+                                               void *out_buf,
+                                               glong n_pixels,
+                                               const GeglRectangle *roi,
+                                               gint level)
+{
+  PhotosOperationSaturation *self = PHOTOS_OPERATION_SATURATION (operation);
+  gfloat *in = in_buf;
+  gfloat *out = out_buf;
+  glong i;
+
+  for (i = 0; i < n_pixels; i++)
+    {
+      out[0] = in[0];
+      out[1] = in[1] * self->scale;
+      out[2] = in[2] * self->scale;
+      out[3] = in[3];
+
+      in += 4;
+      out += 4;
+    }
+}
+
+
+static void
 photos_operation_saturation_process_lch (GeglOperation *operation,
                                          void *in_buf,
                                          void *out_buf,
@@ -109,20 +160,42 @@ photos_operation_saturation_prepare (GeglOperation *operation)
   PhotosOperationSaturation *self = PHOTOS_OPERATION_SATURATION (operation);
   const Babl *format;
   const Babl *input_format;
+  const Babl *model_input;
+  const Babl *model_lch;
 
   input_format = gegl_operation_get_source_format (operation, "input");
   if (input_format == NULL)
     return;
 
+  model_input = babl_format_get_model (input_format);
+
   if (babl_format_has_alpha (input_format))
     {
-      format = babl_format ("CIE LCH(ab) alpha float");
-      self->process = photos_operation_saturation_process_lch_alpha;
+      model_lch = babl_model ("CIE LCH(ab) alpha");
+      if (model_input == model_lch)
+        {
+          format = babl_format ("CIE LCH(ab) alpha float");
+          self->process = photos_operation_saturation_process_lch_alpha;
+        }
+      else
+        {
+          format = babl_format ("CIE Lab alpha float");
+          self->process = photos_operation_saturation_process_lab_alpha;
+        }
     }
   else
     {
-      format = babl_format ("CIE LCH(ab) float");
-      self->process = photos_operation_saturation_process_lch;
+      model_lch = babl_model ("CIE LCH(ab)");
+      if (model_input == model_lch)
+        {
+          format = babl_format ("CIE LCH(ab) float");
+          self->process = photos_operation_saturation_process_lch;
+        }
+      else
+        {
+          format = babl_format ("CIE Lab float");
+          self->process = photos_operation_saturation_process_lab;
+        }
     }
 
   gegl_operation_set_format (operation, "input", format);