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Diffstat (limited to 'plugins/color/gsd-night-light-common.c')
| -rw-r--r-- | plugins/color/gsd-night-light-common.c | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/plugins/color/gsd-night-light-common.c b/plugins/color/gsd-night-light-common.c new file mode 100644 index 0000000..5fe756e --- /dev/null +++ b/plugins/color/gsd-night-light-common.c @@ -0,0 +1,137 @@ +/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 8 -*- + * + * Copyright (C) 2017 Richard Hughes <richard@hughsie.com> + * + * 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; if not, see <http://www.gnu.org/licenses/>. + * + */ + +#include "config.h" + +#include <glib.h> +#include <math.h> + +#include "gsd-night-light-common.h" + +static gdouble +deg2rad (gdouble degrees) +{ + return (M_PI * degrees) / 180.f; +} + +static gdouble +rad2deg (gdouble radians) +{ + return radians * (180.f / M_PI); +} + +/* + * Formulas taken from https://www.esrl.noaa.gov/gmd/grad/solcalc/calcdetails.html + * + * The returned values are fractional hours, so 6am would be 6.0 and 4:30pm + * would be 16.5. + * + * The values returned by this function might not make sense for locations near + * the polar regions. For example, in the north of Lapland there might not be + * a sunrise at all. + */ +gboolean +gsd_night_light_get_sunrise_sunset (GDateTime *dt, + gdouble pos_lat, gdouble pos_long, + gdouble *sunrise, gdouble *sunset) +{ + g_autoptr(GDateTime) dt_zero = g_date_time_new_utc (1900, 1, 1, 0, 0, 0); + GTimeSpan ts = g_date_time_difference (dt, dt_zero); + + g_return_val_if_fail (pos_lat <= 90.f && pos_lat >= -90.f, FALSE); + g_return_val_if_fail (pos_long <= 180.f && pos_long >= -180.f, FALSE); + + gdouble tz_offset = (gdouble) g_date_time_get_utc_offset (dt) / G_USEC_PER_SEC / 60 / 60; // B5 + gdouble date_as_number = ts / G_USEC_PER_SEC / 24 / 60 / 60 + 2; // B7 + gdouble time_past_local_midnight = 0; // E2, unused in this calculation + gdouble julian_day = date_as_number + 2415018.5 + + time_past_local_midnight - tz_offset / 24; + gdouble julian_century = (julian_day - 2451545) / 36525; + gdouble geom_mean_long_sun = fmod (280.46646 + julian_century * + (36000.76983 + julian_century * 0.0003032), 360); // I2 + gdouble geom_mean_anom_sun = 357.52911 + julian_century * + (35999.05029 - 0.0001537 * julian_century); // J2 + gdouble eccent_earth_orbit = 0.016708634 - julian_century * + (0.000042037 + 0.0000001267 * julian_century); // K2 + gdouble sun_eq_of_ctr = sin (deg2rad (geom_mean_anom_sun)) * + (1.914602 - julian_century * (0.004817 + 0.000014 * julian_century)) + + sin (deg2rad (2 * geom_mean_anom_sun)) * (0.019993 - 0.000101 * julian_century) + + sin (deg2rad (3 * geom_mean_anom_sun)) * 0.000289; // L2 + gdouble sun_true_long = geom_mean_long_sun + sun_eq_of_ctr; // M2 + gdouble sun_app_long = sun_true_long - 0.00569 - 0.00478 * + sin (deg2rad (125.04 - 1934.136 * julian_century)); // P2 + gdouble mean_obliq_ecliptic = 23 + (26 + ((21.448 - julian_century * + (46.815 + julian_century * (0.00059 - julian_century * 0.001813)))) / 60) / 60; // Q2 + gdouble obliq_corr = mean_obliq_ecliptic + 0.00256 * + cos (deg2rad (125.04 - 1934.136 * julian_century)); // R2 + gdouble sun_declin = rad2deg (asin (sin (deg2rad (obliq_corr)) * + sin (deg2rad (sun_app_long)))); // T2 + gdouble var_y = tan (deg2rad (obliq_corr/2)) * tan (deg2rad (obliq_corr / 2)); // U2 + gdouble eq_of_time = 4 * rad2deg (var_y * sin (2 * deg2rad (geom_mean_long_sun)) - + 2 * eccent_earth_orbit * sin (deg2rad (geom_mean_anom_sun)) + + 4 * eccent_earth_orbit * var_y * + sin (deg2rad (geom_mean_anom_sun)) * + cos (2 * deg2rad (geom_mean_long_sun)) - + 0.5 * var_y * var_y * sin (4 * deg2rad (geom_mean_long_sun)) - + 1.25 * eccent_earth_orbit * eccent_earth_orbit * + sin (2 * deg2rad (geom_mean_anom_sun))); // V2 + gdouble ha_sunrise = rad2deg (acos (cos (deg2rad (90.833)) / (cos (deg2rad (pos_lat)) * + cos (deg2rad (sun_declin))) - tan (deg2rad (pos_lat)) * + tan (deg2rad (sun_declin)))); // W2 + gdouble solar_noon = (720 - 4 * pos_long - eq_of_time + tz_offset * 60) / 1440; // X2 + gdouble sunrise_time = solar_noon - ha_sunrise * 4 / 1440; // Y2 + gdouble sunset_time = solar_noon + ha_sunrise * 4 / 1440; // Z2 + + /* convert to hours */ + if (sunrise != NULL) + *sunrise = sunrise_time * 24; + if (sunset != NULL) + *sunset = sunset_time * 24; + return TRUE; +} + +gdouble +gsd_night_light_frac_day_from_dt (GDateTime *dt) +{ + return g_date_time_get_hour (dt) + + (gdouble) g_date_time_get_minute (dt) / 60.f + + (gdouble) g_date_time_get_second (dt) / 3600.f; +} + +gboolean +gsd_night_light_frac_day_is_between (gdouble value, + gdouble start, + gdouble end) +{ + /* wrap end to the next day if it is before start, + * considering equal values as a full 24h period + */ + if (end <= start) + end += 24; + + /* wrap value to the next day if it is before the range */ + if (value < start && value < end) + value += 24; + + /* Check whether value falls into range; together with the 24h + * wrap around above this means that TRUE is always returned when + * start == end. + */ + return value >= start && value < end; +} |