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Diffstat (limited to 'src/blackbody.c')
| -rw-r--r-- | src/blackbody.c | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/src/blackbody.c b/src/blackbody.c new file mode 100644 index 0000000..abe03a9 --- /dev/null +++ b/src/blackbody.c @@ -0,0 +1,130 @@ +/** + * Copyright © 2016 Mattias Andrée <maandree@member.fsf.org> + * + * 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 3 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, see <http://www.gnu.org/licenses/>. + */ +#include "blackbody.h" +#include "macros.h" +#include <math.h> +#include <errno.h> + + + +/** + * 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; + + /* 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)); + + /* 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); +} + + +/** + * 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, (double)DELTA_TEMPERATURE) / (double)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. + * + * @param fd File descriptor for the colour table. + * @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 0 The file did not have the expected size. + * @throws EDOM The selected temperature is below 1000 K. + */ +int +get_colour(int fd, long int temp, double *r, double *g, double *b) +{ + double values[10]; /* low:x,y,r,g,b + high:x,y,r,g,b */ + off_t offset; + double max; + + /* We do not have any values for above 40 000 K, but + * the differences will be unnoticeable, perhaps even + * unencodeable. */ + if (temp > HIGHEST_TEMPERATURE) temp = HIGHEST_TEMPERATURE; + /* Things do not glow below 1000 K. Yes, fire is hot! */ + if (temp < LOWEST_TEMPERATURE) t ((errno = EDOM)); + + /* Read table. */ + offset = ((off_t)temp - LOWEST_TEMPERATURE) / DELTA_TEMPERATURE; + offset *= (off_t)(sizeof(values) / 2); + errno = 0; xpread(fd, values, sizeof(values), offset); + + /* Get colour. */ + if (temp % DELTA_TEMPERATURE) + interpolate(values[0], values[1], values[6], values[7], (double)temp, r, g, b); + else + *r = values[2], *g = values[3], *b = values[4]; + + /* Adjust colours for use. */ + max = fmax(fmax(fabs(*r), fabs(*g)), fabs(*b)); + if (max != 0) *r /= max, *g /= max, *b /= max; + *r = *r > 0.0 ? *r : 0.0; + *g = *g > 0.0 ? *g : 0.0; + *b = *b > 0.0 ? *b : 0.0; + + return 0; +fail: + return -1; +} + |