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#include "environment.h"
#include <chronology.h>
#include <gfx/gl/sceneRenderer.h>
Environment::Environment() : worldTime {"2024-01-01T12:00:00"_time_t} { }
void
Environment::tick(TickDuration)
{
worldTime += 50;
}
void
Environment::render(const SceneRenderer & renderer, const SceneProvider & scene) const
{
constexpr RGB baseAmbient {0.1F}, baseDirectional {0.0F};
constexpr RGB relativeAmbient {0.3F, 0.3F, 0.4F}, relativeDirectional {0.6F, 0.6F, 0.5F};
const auto sunPos = getSunPos({}, worldTime);
const auto sunDir = (glm::mat3 {rotate_yp({sunPos.y + pi, sunPos.x})} * north);
const auto vertical = -std::min(0.F, sunDir.z - 0.1F);
const auto ambient = baseAmbient + relativeAmbient * vertical;
const auto directional = baseDirectional + relativeDirectional * vertical;
renderer.setAmbientLight(ambient);
renderer.setDirectionalLight(directional, sunDir, scene);
}
// Based on the C++ code published at https://www.psa.es/sdg/sunpos.htm
// Linked from https://www.pveducation.org/pvcdrom/properties-of-sunlight/suns-position-to-high-accuracy
Direction2D
Environment::getSunPos(const Direction2D position, const time_t time)
{
auto & longitude = position.x;
auto & latitude = position.y;
using std::acos;
using std::asin;
using std::atan2;
using std::cos;
using std::floor;
using std::sin;
using std::tan;
static const auto JD2451545 = "2000-01-01T12:00:00"_time_t;
// Calculate difference in days between the current Julian Day
// and JD 2451545.0, which is noon 1 January 2000 Universal Time
// Calculate time of the day in UT decimal hours
const auto dDecimalHours = static_cast<float>(time % 86400) / 3600.F;
const auto dElapsedJulianDays = static_cast<float>(time - JD2451545) / 86400.F;
// Calculate ecliptic coordinates (ecliptic longitude and obliquity of the
// ecliptic in radians but without limiting the angle to be less than 2*Pi
// (i.e., the result may be greater than 2*Pi)
const auto dOmega = 2.1429F - 0.0010394594F * dElapsedJulianDays;
const auto dMeanLongitude = 4.8950630F + 0.017202791698F * dElapsedJulianDays; // Radians
const auto dMeanAnomaly = 6.2400600F + 0.0172019699F * dElapsedJulianDays;
const auto dEclipticLongitude = dMeanLongitude + 0.03341607F * sin(dMeanAnomaly)
+ 0.00034894F * sin(2 * dMeanAnomaly) - 0.0001134F - 0.0000203F * sin(dOmega);
const auto dEclipticObliquity = 0.4090928F - 6.2140e-9F * dElapsedJulianDays + 0.0000396F * cos(dOmega);
// Calculate celestial coordinates ( right ascension and declination ) in radians
// but without limiting the angle to be less than 2*Pi (i.e., the result may be
// greater than 2*Pi)
const auto dSin_EclipticLongitude = sin(dEclipticLongitude);
const auto dY = cos(dEclipticObliquity) * dSin_EclipticLongitude;
const auto dX = cos(dEclipticLongitude);
auto dRightAscension = atan2(dY, dX);
if (dRightAscension < 0) {
dRightAscension = dRightAscension + two_pi;
}
const auto dDeclination = asin(sin(dEclipticObliquity) * dSin_EclipticLongitude);
// Calculate local coordinates ( azimuth and zenith angle ) in degrees
const auto dGreenwichMeanSiderealTime = 6.6974243242F + 0.0657098283F * dElapsedJulianDays + dDecimalHours;
const auto dLocalMeanSiderealTime
= (dGreenwichMeanSiderealTime * 15.0F + (longitude / degreesToRads)) * degreesToRads;
const auto dHourAngle = dLocalMeanSiderealTime - dRightAscension;
const auto dLatitudeInRadians = latitude;
const auto dCos_Latitude = cos(dLatitudeInRadians);
const auto dSin_Latitude = sin(dLatitudeInRadians);
const auto dCos_HourAngle = cos(dHourAngle);
Direction2D udtSunCoordinates;
udtSunCoordinates.y
= (acos(dCos_Latitude * dCos_HourAngle * cos(dDeclination) + sin(dDeclination) * dSin_Latitude));
udtSunCoordinates.x = atan2(-sin(dHourAngle), tan(dDeclination) * dCos_Latitude - dSin_Latitude * dCos_HourAngle);
if (udtSunCoordinates.x < 0) {
udtSunCoordinates.x = udtSunCoordinates.x + two_pi;
}
// Parallax Correction
const auto dParallax = (earthMeanRadius / astronomicalUnit) * sin(udtSunCoordinates.y);
udtSunCoordinates.y = half_pi - (udtSunCoordinates.y + dParallax);
return udtSunCoordinates;
}
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