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/* See LICENSE file for copyright and license details. */
#if defined(__GNUC__)
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wunsuffixed-float-constants"
#endif
#ifndef LIBRED_COMPILING_PARSER
# include "libred.h"
# include <errno.h>
# include <math.h>
# include <stddef.h>
/**
* Colour temperatures in CIE xy (xyY without Y)
*/
static struct xy {double x, y;} xy_table[] = {
# include "10deg-xy.i"
};
/**
* Colour temperatures in sRGB
*/
static struct rgb {double r, g, b;} rgb_table[] = {
# include "10deg-rgb.i"
};
#endif
/**
* Convert from CIE xyY to [0, 1] sRGB
*
* @param x The 'x' component
* @param y The 'y' component
* @param Y The 'Y' component
* @param r Output parameter for the “red” value
* (Seriously, sRGB red is orange, just look at it fullscreen)
* @param g Output parameter for the green value
* @param b Output parameter for the blue value
*/
static void
ciexyy_to_srgb(double x, double y, double Y, double *r, double *g, double *b)
{
#define SRGB(C) (((C) <= 0.0031308) ? (12.92 * (C)) : ((1.0 + 0.055) * pow((C), 1.0 / 2.4) - 0.055))
double X, Z, max;
#if __GNUC__
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wfloat-equal"
#endif
/* Convert CIE xyY to CIE XYZ */
X = Y * (y == 0.0 ? 0.0 : (x / y));
Z = Y * (y == 0.0 ? 0.0 : ((1.0 - x - y) / y));
#if __GNUC__
# pragma GCC diagnostic pop
#endif
/* Convert CIE XYZ to [0, 1] linear RGB (ciexyz_to_linear) */
*r = ( 3.240450 * X) + (-1.537140 * Y) + (-0.4985320 * Z);
*g = (-0.969266 * X) + ( 1.876010 * Y) + ( 0.0415561 * Z);
*b = (0.0556434 * X) + (-0.204026 * Y) + ( 1.0572300 * Z);
/* Convert [0, 1] linear RGB to [0, 1] sRGB */
SRGB(*r), SRGB(*g), SRGB(*b);
/* Adjust colours for use */
max = fmax(fmax(fabs(*r), fabs(*g)), fabs(*b));
#if __GNUC__
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wfloat-equal"
#endif
if (max != 0.0) *r /= max, *g /= max, *b /= max;
#if __GNUC__
# pragma GCC diagnostic pop
#endif
*r = *r > 0.0 ? *r : 0.0;
*g = *g > 0.0 ? *g : 0.0;
*b = *b > 0.0 ? *b : 0.0;
}
#ifndef LIBRED_COMPILING_PARSER
/**
* Perform linear interpolation (considered very good)
* between the CIE xyY values for two colour temperatures
* and convert the result to sRGB. The two colours should
* be the closest below the desired colour temperature,
* and the closest above the desired colour temperature
*
* @param x1 The 'x' component for the low colour
* @param y1 The 'y' component for the low colour
* @param x2 The 'x' component for the high colour
* @param y2 The 'y' component for the high colour
* @param temp The desired colour temperature
* @param r Output parameter for the “red” value
* @param g Output parameter for the green value
* @param b Output parameter for the blue value
*/
static void
interpolate(double x1, double y1, double x2, double y2, double temp, double *r, double *g, double *b)
{
double weight = fmod(temp - (LIBRED_LOWEST_TEMPERATURE % LIBRED_DELTA_TEMPERATURE),
(double)LIBRED_DELTA_TEMPERATURE) / (double)LIBRED_DELTA_TEMPERATURE;
double x = x1 * (1 - weight) + x2 * weight;
double y = y1 * (1 - weight) + y2 * weight;
ciexyy_to_srgb(x, y, 1.0, r, g, b);
}
/**
* Get the [0, 1] sRGB values of a colour temperature
*
* libred has a table of colour temperature values, this
* function interpolates values that are missing. If you
* don't want any interpolation the `temp` parameter can
* be specified in one of the following ways:
*
* - floor:
* (temp - LIBRED_LOWEST_TEMPERATURE) /
* LIBRED_DELTA_TEMPERATURE *
* LIBRED_DELTA_TEMPERATURE +
* LIBRED_LOWEST_TEMPERATURE
*
* - ceiling:
* (temp - LIBRED_LOWEST_TEMPERATURE +
* LIBRED_DELTA_TEMPERATURE - 1) /
* LIBRED_DELTA_TEMPERATURE *
* LIBRED_DELTA_TEMPERATURE +
* LIBRED_LOWEST_TEMPERATURE
*
* - round to nearest:
* (temp - LIBRED_LOWEST_TEMPERATURE +
* LIBRED_DELTA_TEMPERATURE / 2) /
* LIBRED_DELTA_TEMPERATURE *
* LIBRED_DELTA_TEMPERATURE +
* LIBRED_LOWEST_TEMPERATURE
*
* @param temp The desired colour temperature
* @param r Output parameter for the “red” value
* @param g Output parameter for the green value
* @param b Output parameter for the blue value
* @return 0 on succeess, -1 on error
* @throws EDOM The selected temperature is below 1000K
*/
int
libred_get_colour(long int temp, double *r, double *g, double *b)
{
double x1, y1, x2, y2;
size_t i;
long int tmp;
if (temp > LIBRED_HIGHEST_TEMPERATURE)
temp = LIBRED_HIGHEST_TEMPERATURE;
if (temp < LIBRED_LOWEST_TEMPERATURE) {
errno = EDOM;
return -1;
}
tmp = temp - LIBRED_LOWEST_TEMPERATURE;
i = (size_t)(tmp / LIBRED_DELTA_TEMPERATURE);
if (tmp % LIBRED_DELTA_TEMPERATURE) {
x1 = xy_table[i].x;
y1 = xy_table[i].y;
x2 = xy_table[i + 1].x;
y2 = xy_table[i + 1].y;
interpolate(x1, y1, x2, y2, (double)temp, r, g, b);
} else {
*r = rgb_table[i].r;
*g = rgb_table[i].g;
*b = rgb_table[i].b;
}
return 0;
}
#endif
#if __GNUC__
# pragma GCC diagnostic pop
#endif
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