wrlib/color.c

   1 /* color.c - color stuff (rgb -> hsv convertion etc.)
   2  *
   3  *  Raster graphics library
   4  *
   5  *  Copyright (c) 1998-2002 Alfredo K. Kojima
   6  *
   7  *  This library is free software; you can redistribute it and/or
   8  *  modify it under the terms of the GNU Library General Public
   9  *  License as published by the Free Software Foundation; either
  10  *  version 2 of the License, or (at your option) any later version.
  11  *
  12  *  This library is distributed in the hope that it will be useful,
  13  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  *  Library General Public License for more details.
  16  *
  17  *  You should have received a copy of the GNU Library General Public
  18  *  License along with this library; if not, write to the Free
  19  *  Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20  */
  21
  22 #include <config.h>
  23
  24
  25 #include <stdlib.h>
  26 #include <stdio.h>
  27 #include <string.h>
  28 #include <X11/Xlib.h>
  29
  30 #include <assert.h>
  31
  32 #include "wraster.h"
  33
  34
  35
  36 #define MIN(a,b)        ((a)<(b) ? (a) : (b))
  37 #define MAX(a,b)        ((a)>(b) ? (a) : (b))
  38
  39 #define MIN3(a,b,c)     MIN(MIN(a,b), c)
  40 #define MAX3(a,b,c)     MAX(MAX(a,b), c)
  41
  42
  43 void
  44 RHSVtoRGB(RHSVColor *hsv, RColor *rgb)
  45 {
  46     int h = hsv->hue % 360;
  47     int s = hsv->saturation;
  48     int v = hsv->value;
  49     int i, f;
  50     int p, q, t;
  51
  52     if (s == 0) {
  53         rgb->red = rgb->green = rgb->blue = v;
  54         return;
  55     }
  56     i = h / 60;
  57     f = h % 60;
  58     p = v * (255 - s) / 255;
  59     q = v * (255 - s * f / 60) / 255;
  60     t = v * (255 - s * (60 - f) / 60) / 255;
  61
  62     switch (i) {
  63       case 0:
  64         rgb->red = v;
  65         rgb->green = t;
  66         rgb->blue = p;
  67         break;
  68       case 1:
  69         rgb->red = q;
  70         rgb->green = v;
  71         rgb->blue = p;
  72         break;
  73       case 2:
  74         rgb->red = p;
  75         rgb->green = v;
  76         rgb->blue = t;
  77         break;
  78       case 3:
  79         rgb->red = p;
  80         rgb->green = q;
  81         rgb->blue = v;
  82         break;
  83       case 4:
  84         rgb->red = t;
  85         rgb->green = p;
  86         rgb->blue = v;
  87         break;
  88       case 5:
  89         rgb->red = v;
  90         rgb->green = p;
  91         rgb->blue = q;
  92         break;
  93     }
  94 }
  95
  96
  97 void
  98 RRGBtoHSV(RColor *rgb, RHSVColor *hsv)
  99 {
 100     int h, s, v;
 101     int max = MAX3(rgb->red, rgb->green, rgb->blue);
 102     int min = MIN3(rgb->red, rgb->green, rgb->blue);
 103
 104     v = max;
 105
 106     if (max == 0)
 107         s = 0;
 108     else
 109         s = (max - min) * 255 / max;
 110
 111     if (s == 0)
 112         h = 0;
 113     else {
 114         int rc, gc, bc;
 115
 116         rc = (max - rgb->red) * 255 / (max - min);
 117         gc = (max - rgb->green) * 255 / (max - min);
 118         bc = (max - rgb->blue) * 255 / (max - min);
 119
 120         if (rgb->red == max) {
 121             h = ((bc - gc) * 60 / 255);
 122         } else if (rgb->green == max) {
 123             h = 2*60 + ((rc - bc) * 60 / 255);
 124         } else {
 125             h = 4*60 + ((gc - rc) * 60 / 255);
 126         }
 127         if (h < 0)
 128             h += 360;
 129     }
 130
 131     hsv->hue = h;
 132     hsv->saturation = s;
 133     hsv->value = v;
 134 }