4 files changed, 117 insertions, 0 deletions
diff --git a/game/environment.cpp b/game/environment.cpp
new file mode 100644
index 0000000..19aad84
--- /dev/null
+++ b/game/environment.cpp
@@ -0,0 +1,94 @@
+#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;
+}
diff --git a/game/environment.h b/game/environment.h
new file mode 100644
index 0000000..a6f3036
--- /dev/null
+++ b/game/environment.h
@@ -0,0 +1,18 @@
+#pragma once
+
+#include "config/types.h"
+#include "worldobject.h"
+
+class SceneRenderer;
+class SceneProvider;
+
+class Environment : public WorldObject {
+public:
+	Environment();
+	void tick(TickDuration elapsed) override;
+	void render(const SceneRenderer &, const SceneProvider &) const;
+	static Direction2D getSunPos(const Direction2D position, const time_t time);
+
+private:
+	time_t worldTime;
+};
diff --git a/game/gamestate.cpp b/game/gamestate.cpp
index fcd4248..910e8a7 100644
--- a/game/gamestate.cpp
+++ b/game/gamestate.cpp
@@ -1,4 +1,5 @@
 #include "gamestate.h"
+#include "environment.h"
 #include <cassert>
 
 GameState * gameState {nullptr};
@@ -7,6 +8,8 @@ GameState::GameState()
 {
 	assert(!gameState);
 	gameState = this;
+
+	environment = world.create<Environment>();
 }
 
 GameState::~GameState()
diff --git a/game/gamestate.h b/game/gamestate.h
index f07f844..892aa69 100644
--- a/game/gamestate.h
+++ b/game/gamestate.h
@@ -7,6 +7,7 @@
 
 class WorldObject;
 class GeoData;
+class Environment;
 
 class GameState {
 public:
@@ -17,6 +18,7 @@ public:
 
 	Collection<WorldObject> world;
 	std::shared_ptr<GeoData> geoData;
+	std::shared_ptr<Environment> environment;
 	AssetFactory::Assets assets;
 };