color_str.c

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/*!
   \file lib/gis/color_str.c
 
   \brief GIS library - color management, named color to RGB triplet
 
   (C) 2001-2016 by the GRASS Development Team
 
   This program is free software under the
   GNU General Public License (>=v2).
   Read the file COPYING that comes with GRASS
   for details.
 
   \author Original author CERL
 */
 
#include <math.h>
#include <string.h>
 
#include <grass/gis.h>
#include <grass/colors.h>
 
/* The order in this table is important! It will be indexed by color number */
static const struct color_rgb standard_colors_rgb[] = {
    {0, 0, 0},       /* This is a dummy value to make lookup easier */
    {0, 0, 0},       /* BLACK   */
    {255, 0, 0},     /* RED     */
    {0, 255, 0},     /* GREEN   */
    {0, 0, 255},     /* BLUE    */
    {255, 255, 0},   /* YELLOW  */
    {0, 255, 255},   /* CYAN    */
    {255, 0, 255},   /* MAGENTA */
    {255, 255, 255}, /* WHITE   */
    {128, 128, 128}, /* GRAY    */
    {255, 128, 0},   /* ORANGE  */
    {100, 128, 255}, /* AQUA    */
    {0, 128, 255},   /* INDIGO  */
    {128, 0, 255},   /* VIOLET  */
    {180, 77, 25}    /* BROWN   */
};
 
/* The order in this table has no meaning. */
static const struct color_name standard_color_names[] = {
    {"black", BLACK},     {"red", RED},       {"green", GREEN},
    {"blue", BLUE},       {"yellow", YELLOW}, {"cyan", CYAN},
    {"magenta", MAGENTA}, {"white", WHITE},   {"grey", GREY},
    {"gray", GRAY},       {"orange", ORANGE}, {"aqua", AQUA},
    {"indigo", INDIGO},   {"violet", VIOLET}, {"purple", PURPLE},
    {"brown", BROWN}};
 
/*!
   \brief Get number of named colors (RGB triplets)
 
   \return number of colors
 */
int G_num_standard_colors(void)
{
    return sizeof(standard_colors_rgb) / sizeof(standard_colors_rgb[0]);
}
 
/*!
   \brief Get RGB triplet of given color
 
   \param n color index
 */
struct color_rgb G_standard_color_rgb(int n)
{
    return standard_colors_rgb[n];
}
 
/*!
   \brief Get number of named colors (color names)
 
   \return number of colors
 */
int G_num_standard_color_names(void)
{
    return sizeof(standard_color_names) / sizeof(standard_color_names[0]);
}
 
/*!
   \brief Get color name
 
   \param n color index
 */
const struct color_name *G_standard_color_name(int n)
{
    return &standard_color_names[n];
}
 
/*!
   \brief Parse color string and set red,green,blue
 
   \param str color string
   \param[out] red red value
   \param[out] grn green value
   \param[out] blu blue value
 
   \return 1 OK
   \return 2 NONE
   \return 0 on error
 */
int G_str_to_color(const char *str, int *red, int *grn, int *blu)
{
    char buf[100];
    int num_names = G_num_standard_color_names();
    int i;
 
    strcpy(buf, str);
    G_chop(buf);
 
    G_debug(3, "G_str_to_color(): str = '%s'", buf);
 
    if (G_strcasecmp(buf, "NONE") == 0)
        return 2;
 
    if (sscanf(buf, "%d%*[,:; ]%d%*[,:; ]%d", red, grn, blu) == 3) {
        if (*red < 0 || *red > 255 || *grn < 0 || *grn > 255 || *blu < 0 ||
            *blu > 255)
            return 0;
 
        return 1;
    }
 
    unsigned int hex;
 
    if (sscanf(buf, "#%x", &hex) == 1) {
        *red = (hex >> 16) & 0xFF;
        *grn = (hex >> 8) & 0xFF;
        *blu = hex & 0xFF;
        if (*red < 0 || *red > 255 || *grn < 0 || *grn > 255 || *blu < 0 ||
            *blu > 255)
            return 0;
 
        return 1;
    }
 
    /* Look for this color in the standard (preallocated) colors */
    for (i = 0; i < num_names; i++) {
        const struct color_name *name = &standard_color_names[i];
 
        if (G_strcasecmp(buf, name->name) == 0) {
            struct color_rgb rgb = standard_colors_rgb[name->number];
 
            *red = (int)rgb.r;
            *grn = (int)rgb.g;
            *blu = (int)rgb.b;
 
            return 1;
        }
    }
 
    return 0;
}
 
/*!
   \brief Converts RGB color values to HSV format.
 
   \note This implementation is experimental and may be subject to change.
 
   \param r red component of the RGB color
   \param g green component of the RGB color
   \param b blue component of the RGB color
   \param[out] h pointer to store the calculated hue
   \param[out] s pointer to store the calculated saturation
   \param[out] v pointer to store the calculated value
 */
void G_rgb_to_hsv(int r, int g, int b, float *h, float *s, float *v)
{
    float r_norm = (float)r / 255.0f;
    float g_norm = (float)g / 255.0f;
    float b_norm = (float)b / 255.0f;
 
    float cmax = MAX(r_norm, MAX(g_norm, b_norm));
    float cmin = MIN(r_norm, MIN(g_norm, b_norm));
    float diff = cmax - cmin;
 
    if (cmax == cmin) {
        *h = 0;
    }
    else if (cmax == r_norm) {
        *h = fmodf((60.0f * ((g_norm - b_norm) / diff) + 360.0f), 360.0f);
    }
    else if (cmax == g_norm) {
        *h = fmodf((60.0f * ((b_norm - r_norm) / diff) + 120.0f), 360.0f);
    }
    else {
        *h = fmodf((60.0f * ((r_norm - g_norm) / diff) + 240.0f), 360.0f);
    }
 
    if (cmax == 0) {
        *s = 0;
    }
    else {
        *s = (diff / cmax) * 100.0f;
    }
 
    *v = cmax * 100.0f;
}