[gimp] libgimpcolor: optimize gimp_color_profile_get_format() for cairo-RGB24

[Michael Natterer <mitch src gnome org>]

commit 7326f346c37b3f200086c9a0118ed994902c1aa4
Author: Michael Natterer <mitch gimp org>
Date:   Wed May 25 12:24:06 2016 +0200

    libgimpcolor: optimize gimp_color_profile_get_format() for cairo-RGB24
    
    Trick lcms into converting cairo-RGB24 pixels directly, by using
    TYPE_BGRA_8 on little endian and TYPE_ARGB_8 on big endian. They have
    the same byte order, and the alpha channel (ignored by lcms anyway)
    takes the place of the unused byte of cairo-RGB24.
    
    This saves two babl conversions around cmsDoTransform().

 libgimpcolor/gimpcolorprofile.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/libgimpcolor/gimpcolorprofile.c b/libgimpcolor/gimpcolorprofile.c
index 93f291c..385a79b 100644
--- a/libgimpcolor/gimpcolorprofile.c
+++ b/libgimpcolor/gimpcolorprofile.c
@@ -1480,9 +1480,13 @@ gimp_color_profile_get_format (const Babl *format,
 
   if (format == babl_format ("cairo-RGB24"))
     {
-      *lcms_format = TYPE_RGB_8;
+#if G_BYTE_ORDER == G_LITTLE_ENDIAN
+      *lcms_format = TYPE_BGRA_8;
+#else
+      *lcms_format = TYPE_ARGB_8;
+#endif
 
-      return babl_format ("R'G'B' u8");
+      return format;
     }
   else if (format == babl_format ("cairo-ARGB32"))
     {