color.h

/*
	DDS GIMP plugin

	Copyright (C) 2004-2012 Shawn Kirst <skirst@gmail.com>,
   with parts (C) 2003 Arne Reuter <homepage@arnereuter.de> where specified.

	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; see the file COPYING.  If not, write to
	the Free Software Foundation, 51 Franklin Street, Fifth Floor
	Boston, MA 02110-1301, USA.
*/

#ifndef COLOR_H
#define COLOR_H

#include "imath.h"

/* sRGB encoding/decoding */
int linear_to_sRGB(int c);
int sRGB_to_linear(int c);

/* YCoCg encoding */
static inline void RGB_to_YCoCg(unsigned char *dst, int r, int g, int b)
{
   int y  = ((r +     (g << 1) + b) + 2) >> 2;
   int co = ((((r << 1) - (b << 1)) + 2) >> 2) + 128;
   int cg = (((-r +   (g << 1) - b) + 2) >> 2) + 128;

   dst[0] = 255;
   dst[1] = (cg > 255 ? 255 : (cg < 0 ? 0 : cg));
   dst[2] = (co > 255 ? 255 : (co < 0 ? 0 : co));
   dst[3] = (y  > 255 ? 255 : (y  < 0 ? 0 :  y));
}

/* other color conversions */

static inline int rgb_to_luminance(int r, int g, int b)
{
   /* ITU-R BT.709 luma coefficents, scaled by 256 */
   return(((r * 54 + g * 182 + b * 20) + 128) >> 8);
}

static inline unsigned short pack_r5g6b5(int r, int g, int b)
{
   return((mul8bit(r, 31) << 11) |
          (mul8bit(g, 63) <<  5) |
          (mul8bit(b, 31)      ));
}

static inline unsigned short pack_rgba4(int r, int g, int b, int a)
{
   return((mul8bit(a, 15) << 12) |
          (mul8bit(r, 15) <<  8) |
          (mul8bit(g, 15) <<  4) |
          (mul8bit(b, 15)      ));
}

static inline unsigned short pack_rgb5a1(int r, int g, int b, int a)
{
   return((((a >> 7) & 0x01) << 15) |
          (mul8bit(r, 31)    << 10) |
          (mul8bit(g, 31)    <<  5) |
          (mul8bit(b, 31)         ));
}

static inline unsigned char pack_r3g3b2(int r, int g, int b)
{
   return((mul8bit(r, 7) << 5) |
          (mul8bit(g, 7) << 2) |
          (mul8bit(b, 3)     ));
}

static inline unsigned int pack_rgb10a2(int r, int g, int b, int a)
{
   return(((unsigned int)((a >> 6) & 0x003) << 30) |
          ((unsigned int)((r << 2) & 0x3ff) << 20) |
          ((unsigned int)((g << 2) & 0x3ff) << 10) |
          ((unsigned int)((b << 2) & 0x3ff)      ));
}

#endif