libgimpwidgets: add gimp_widget_get_color_transform()

Which returns a GimpColorTransform to transform a GimpColorManaged's
pixels to a GtkWidget's color space, using a GimpColorConfig's
settings. This is *unfinished* API and in the end will enable simple
display color management for the app, libgimp and plug-ins.

libgimpwidgets/gimpwidgetsutils.c

@@ -31,10 +31,13 @@
 #include <CoreServices/CoreServices.h>
 #endif
 
+#include <lcms2.h>
+
 #include <gegl.h>
 #include <gtk/gtk.h>
 
 #include "libgimpcolor/gimpcolor.h"
+#include "libgimpconfig/gimpconfig.h"
 
 #include "gimpwidgetstypes.h"
 
@@ -455,3 +458,154 @@ gimp_widget_get_color_profile (GtkWidget *widget)
 
   return profile;
 }
+
+static GimpColorProfile
+get_rgb_profile (GimpColorManaged *managed,
+                 GimpColorConfig  *config)
+{
+  GimpColorProfile  profile = NULL;
+  const guint8     *data;
+  gsize             len;
+
+  data = gimp_color_managed_get_icc_profile (managed, &len);
+
+  if (data)
+    profile = gimp_lcms_profile_open_from_data (data, len, NULL);
+
+  if (profile && ! gimp_lcms_profile_is_rgb (profile))
+    {
+      gimp_lcms_profile_close (profile);
+      profile = NULL;
+    }
+
+  if (! profile)
+    profile = gimp_color_config_get_rgb_profile (config, NULL);
+
+  return profile;
+}
+
+static GimpColorProfile
+get_display_profile (GtkWidget       *widget,
+                     GimpColorConfig *config)
+{
+  GimpColorProfile profile;
+
+  profile = gimp_widget_get_color_profile (widget);
+
+  if (! profile)
+    profile = gimp_color_config_get_display_profile (config, NULL);
+
+  return profile;
+}
+
+GimpColorTransform
+gimp_widget_get_color_transform (GtkWidget        *widget,
+                                 GimpColorManaged *managed,
+                                 GimpColorConfig  *config,
+                                 const Babl       *src_format,
+                                 const Babl       *dest_format)
+{
+  GimpColorTransform transform     = NULL;
+  GimpColorProfile   src_profile   = NULL;
+  GimpColorProfile   dest_profile  = NULL;
+  GimpColorProfile   proof_profile = NULL;
+  cmsUInt32Number    lcms_src_format;
+  cmsUInt32Number    lcms_dest_format;
+  cmsUInt16Number    alarmCodes[cmsMAXCHANNELS] = { 0, };
+
+  g_return_val_if_fail (widget == NULL || GTK_IS_WIDGET (widget), NULL);
+  g_return_val_if_fail (GIMP_IS_COLOR_MANAGED (managed), NULL);
+  g_return_val_if_fail (GIMP_IS_COLOR_CONFIG (config), NULL);
+  g_return_val_if_fail (src_format != NULL, NULL);
+  g_return_val_if_fail (dest_format != NULL, NULL);
+
+  switch (config->mode)
+    {
+    case GIMP_COLOR_MANAGEMENT_OFF:
+      return NULL;
+
+    case GIMP_COLOR_MANAGEMENT_SOFTPROOF:
+      proof_profile = gimp_color_config_get_printer_profile (config, NULL);
+      /*  fallthru  */
+
+    case GIMP_COLOR_MANAGEMENT_DISPLAY:
+      src_profile  = get_rgb_profile (managed, config);
+      dest_profile = get_display_profile (widget, config);
+      break;
+    }
+
+  src_format  = gimp_lcms_get_format (src_format,  &lcms_src_format);
+  dest_format = gimp_lcms_get_format (dest_format, &lcms_dest_format);
+
+  if (proof_profile)
+    {
+      cmsUInt32Number softproof_flags = 0;
+
+      if (! src_profile)
+        src_profile = gimp_lcms_create_srgb_profile ();
+
+      if (! dest_profile)
+        dest_profile = gimp_lcms_create_srgb_profile ();
+
+      softproof_flags |= cmsFLAGS_SOFTPROOFING;
+
+      if (config->simulation_use_black_point_compensation)
+        {
+          softproof_flags |= cmsFLAGS_BLACKPOINTCOMPENSATION;
+        }
+
+      if (config->simulation_gamut_check)
+        {
+          guchar r, g, b;
+
+          softproof_flags |= cmsFLAGS_GAMUTCHECK;
+
+          gimp_rgb_get_uchar (&config->out_of_gamut_color, &r, &g, &b);
+
+          alarmCodes[0] = (cmsUInt16Number) r * 256;
+          alarmCodes[1] = (cmsUInt16Number) g * 256;
+          alarmCodes[2] = (cmsUInt16Number) b * 256;
+
+          cmsSetAlarmCodes (alarmCodes);
+        }
+
+      transform =
+        cmsCreateProofingTransform (src_profile,  lcms_src_format,
+                                    dest_profile, lcms_dest_format,
+                                    proof_profile,
+                                    config->simulation_intent,
+                                    config->display_intent,
+                                    softproof_flags);
+
+      gimp_lcms_profile_close (proof_profile);
+    }
+  else if (src_profile || dest_profile)
+    {
+      cmsUInt32Number display_flags = 0;
+
+      if (! src_profile)
+        src_profile = gimp_lcms_create_srgb_profile ();
+
+      if (! dest_profile)
+        dest_profile = gimp_lcms_create_srgb_profile ();
+
+      if (config->display_use_black_point_compensation)
+        {
+          display_flags |= cmsFLAGS_BLACKPOINTCOMPENSATION;
+        }
+
+      transform =
+        cmsCreateTransform (src_profile,  lcms_src_format,
+                            dest_profile, lcms_dest_format,
+                            config->display_intent,
+                            display_flags);
+    }
+
+  if (src_profile)
+    gimp_lcms_profile_close (src_profile);
+
+  if (dest_profile)
+    gimp_lcms_profile_close (dest_profile);
+
+  return transform;
+}