Add a gamma correction function

simgear/screen/Makefile.am

@@ -12,10 +12,10 @@ IMAGE_SERVER_INCL =
 IMAGE_SERVER_SRCS = 
 endif
 
-noinst_HEADERS = \
+noinst_HEADERS = colours.h
-        colours.h
 
 include_HEADERS = \
+	colors.hxx \
 	texture.hxx \
 	$(IMAGE_SERVER_INCL) \
 	screen-dump.hxx \

simgear/screen/colors.hxx

@@ -0,0 +1,50 @@
+// colours.h 
+//
+// -- This header file contains color related functions
+//
+// Copyright (C) 2003  FlightGear Flight Simulator
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+//
+// $Id$
+
+
+#ifndef _SG_COLORS_HXX
+#define _SG_COLORS_HXX 1
+
+#include <math.h>
+
+#if defined( macintosh )
+const float system_gamma = 1.4;
+
+#elif defined (sgi)
+const float system_gamma = 1.7;
+
+#else	// others
+const float system_gamma = 2.5;
+#endif
+
+
+// simple architecture independant gamma correction function.
+inline void gamma_correct(float *color,
+                          float reff = 2.5, float system = system_gamma)
+{
+   color[0] = pow(color[0], reff/system);
+   color[1] = pow(color[1], reff/system);
+   color[2] = pow(color[2], reff/system);
+};
+
+#endif // _SG_COLORS_HXX
+