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-rw-r--r--game/environment.cpp94
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diff --git a/game/environment.cpp b/game/environment.cpp
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+++ b/game/environment.cpp
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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;
+}