基础概念

一个星球（例如地球）的气候系统主要是一些基本参数基于公转周期（年）和自转周期（日）的变化，这其中会有两个变化因素：地理位置（经纬度）和天气变化（冷暖空气流动或台风等）。

公转、自转及时间

时间决定于星球的公转周期形成年、星球的自转周期形成日，其下可以更细分出来月、时分秒等。

另外以地球为例，计时还和经度（时区）相关，部分区域可能还有夏令时等。维度决定了日出日落时间的区别，比如会出现极昼极夜等。

基本气候参数

温度：

湿度：

压强：

云量：

日照强度：

风速（方向、强度）：

降雨强度：

降雪强度：

雾霾（颜色、强度）：

雷暴：打雷闪电出现的频次和强度

另外有些衍生参数：

积水量：

积雪量：

积尘量：

气候影响因素

时间变化（四季和昼夜）：

全年随着四季变化，各种基础参数指标会有个变化的曲线；基本所有的气候参数的基础值从这里产生；

极昼太阳远近会有基础气候参数变化，极夜太阳远近也有一些基础气候参数变化（可能比较小），然后中间维度区域在日出和日落事件发生后会逐渐做昼夜切换。

天气变化：

由于随机变化的冷暖气流变化，引起短期和随机的基础气候变化。可以分为：降水天气（雨、雪、冰雹）、雷暴天气、雾霾天气、强风天气（含飓风）。注意部分天气可能会同时发生，比如雷阵雨，同时包含下雨和雷暴甚至同时包含狂风。

游戏逻辑：

由于特殊的技能需要或者BOSS状态等也可能会引起气候参数的变化，此类状态变化独立于自然气候变化并且具有更高优先级，消失后会过渡回自然天气。

系统设计

中间全局管理器ClimateCoordinator用来管理各种基本气候参数，并且会在当前参数值和目标参数值之间做自然过渡。

特定区域内的气候可以根据四季、昼夜等时间变化做变化，另外会有一系列区域内会出现的天气变化，他们应用时也会影响区域内的基础气象参数。游戏逻辑可以在任何时候直接操作ClimateCoordinator来实现从自然天气到游戏逻辑参数的过渡。

对于需要根据气候表现做表演的对象，直接根据ClimateCoordinator中的值来进行对应值修改或者效果表现即可，如果表现参数和气候参数不直接对应可以添加中间对象转换。

方案

中间状态ClimateCoordinator

class CLIMATERUNTIME_API UClimateCoordinator : public UTickableWorldSubsystem
{
...void RegistVolume(AClimateVolume* Volume);void UnRegistVolume(AClimateVolume* Volume);void BindEarthGlobalInfo(UClimateEarthGlobalInfoComponent* Component);void UnbindEarthGlobalInfo(UClimateEarthGlobalInfoComponent* Component);// 0~1: degree of a yearUFUNCTION(BlueprintCallable, Category = "RuntimeClimate|DateTime")const float GetYearDegree() const;// 0~1: degree of a dayUFUNCTION(BlueprintCallable, Category = "RuntimeClimate|DateTime")const float GetDayDegree() const;UFUNCTION(BlueprintCallable, Category = "RuntimeClimate|DateTime")const FDateTime GetDateTime() const { return AreaDateTime; }UFUNCTION(BlueprintCallable, Category = "RuntimeClimate|DateTime")void SetDateTime(const FDateTime& DateTime) { AreaDateTime = DateTime; }UFUNCTION(BlueprintCallable, Category = "RuntimeClimate")const int32 GetTimeScalar() const;UFUNCTION(BlueprintCallable, Category = "RuntimeClimate")void SetTimeScalar(const int32 TimeScalar);UFUNCTION(BlueprintCallable, Category = "RuntimeClimate|Weather")void OverwriteTemperature(bool bOverwirte, const float Temperature, const float FadeDuration);UFUNCTION(BlueprintCallable, Category = "RuntimeClimate|Weather")const float GetTemperature() const;UFUNCTION(BlueprintCallable, Category = "RuntimeClimate|Weather")void OverwriteHumidity(bool bOverwirte, const float Humidity, const float FadeDuration);UFUNCTION(BlueprintCallable, Category = "RuntimeClimate|Weather")const float GetHumidity() const;
...
}

地理信息

class AEarthInfo : public AInfo
{
...float Latitude = 45.0f;float Longitude = -73.0f;float NorthOffset = 0;float BaseElevation = 0;int32 TimeZone = -5.0;int32 Year = 2022;int32 Month = 5;int32 Day = 17;int32 Hours = 12;int32 Minutes = 0;int32 Seconds = 0;uint8 bIsDaylightSavingTime : 1;int32 DSTStartMonth = 6;int32 DSTStartDay = 1;int32 DSTEndMonth = 8;int32 DSTEndDay = 31;int32 TimeScalar = 0;...
}

区域气候盒子

class CLIMATERUNTIME_API AClimateVolume : public AVolume
{
...int32 Priority = 0;uint32 bEnabled : 1;uint32 bUnbound : 1;virtual void PostRegisterAllComponents() override;virtual void PostUnregisterAllComponents() override;virtual void Tick(float DeltaSeconds) override;uint32 bTemperatureValid : 1;float Temperature = 20;float TemperatureUpdateSpeed = 0.01;
...
}

一系列表演辅助类

雾效影响组件：

UCLASS(ClassGroup = (Climate), meta = (BlueprintSpawnableComponent))
class CLIMATERUNTIME_API UClimateFogComponent : public UActorComponent
{GENERATED_UCLASS_BODY()public:virtual void OnRegister() override;virtual void OnUnregister() override;virtual void TickComponent(float DeltaTime, enum ELevelTick TickType, FActorComponentTickFunction* ThisTickFunction) override;UPROPERTY(EditAnywhere, Category = ExponentialHeightFog)FRuntimeFloatCurve ExponentialHeightFogDensityCurveFloat;UPROPERTY(EditAnywhere, Category = ExponentialHeightFog)FRuntimeCurveLinearColor ExponentialHeightFogScatteringColorCurveFloat;private:UPROPERTY(Transient)class UExponentialHeightFogComponent* ManagedComponent = nullptr;UPROPERTY(Transient)class UClimateCoordinator* ClimateCoordinator = nullptr;
};

根据经纬度、时区等信息计算日出、日落时间的计算函数：

void CalcSunPositionByLocationAndDateTime(float Latitude, float Longitude, float TimeZone, bool bIsDaylightSavingTime, const FDateTime& CalcTime, FClimateSunPosition& SunPositionData)
{float TimeOffset = TimeZone;if (bIsDaylightSavingTime){TimeOffset += 1.0f;}double LatitudeRad = FMath::DegreesToRadians(Latitude);// Get the julian day (number of days since Jan 1st of the year 4713 BC)double JulianDay = CalcTime.GetJulianDay() + (CalcTime.GetTimeOfDay().GetTotalHours() - TimeOffset) / 24.0;double JulianCentury = (JulianDay - 2451545.0) / 36525.0;// Get the sun's mean longitude , referred to the mean equinox of julian datedouble GeomMeanLongSunDeg = FMath::Fmod(280.46646 + JulianCentury * (36000.76983 + JulianCentury * 0.0003032), 360.0);double GeomMeanLongSunRad = FMath::DegreesToRadians(GeomMeanLongSunDeg);// Get the sun's mean anomalydouble GeomMeanAnomSunDeg = 357.52911 + JulianCentury * (35999.05029 - 0.0001537 * JulianCentury);double GeomMeanAnomSunRad = FMath::DegreesToRadians(GeomMeanAnomSunDeg);// Get the earth's orbit eccentricitydouble EccentEarthOrbit = 0.016708634 - JulianCentury * (0.000042037 + 0.0000001267 * JulianCentury);// Get the sun's equation of the centerdouble SunEqOfCtr = FMath::Sin(GeomMeanAnomSunRad) * (1.914602 - JulianCentury * (0.004817 + 0.000014 * JulianCentury))+ FMath::Sin(2.0 * GeomMeanAnomSunRad) * (0.019993 - 0.000101 * JulianCentury)+ FMath::Sin(3.0 * GeomMeanAnomSunRad) * 0.000289;// Get the sun's true longitudedouble SunTrueLongDeg = GeomMeanLongSunDeg + SunEqOfCtr;// Get the sun's true anomaly//	double SunTrueAnomDeg = GeomMeanAnomSunDeg + SunEqOfCtr;//	double SunTrueAnomRad = FMath::DegreesToRadians(SunTrueAnomDeg);// Get the earth's distance from the sun//	double SunRadVectorAUs = (1.000001018*(1.0 - EccentEarthOrbit*EccentEarthOrbit)) / (1.0 + EccentEarthOrbit*FMath::Cos(SunTrueAnomRad));// Get the sun's apparent longitudedouble SunAppLongDeg = SunTrueLongDeg - 0.00569 - 0.00478 * FMath::Sin(FMath::DegreesToRadians(125.04 - 1934.136 * JulianCentury));double SunAppLongRad = FMath::DegreesToRadians(SunAppLongDeg);// Get the earth's mean obliquity of the eclipticdouble MeanObliqEclipticDeg = 23.0 + (26.0 + ((21.448 - JulianCentury * (46.815 + JulianCentury * (0.00059 - JulianCentury * 0.001813)))) / 60.0) / 60.0;// Get the oblique correctiondouble ObliqCorrDeg = MeanObliqEclipticDeg + 0.00256 * FMath::Cos(FMath::DegreesToRadians(125.04 - 1934.136 * JulianCentury));double ObliqCorrRad = FMath::DegreesToRadians(ObliqCorrDeg);// Get the sun's right ascensiondouble SunRtAscenRad = FMath::Atan2(FMath::Cos(ObliqCorrRad) * FMath::Sin(SunAppLongRad), FMath::Cos(SunAppLongRad));double SunRtAscenDeg = FMath::RadiansToDegrees(SunRtAscenRad);// Get the sun's declinationdouble SunDeclinRad = FMath::Asin(FMath::Sin(ObliqCorrRad) * FMath::Sin(SunAppLongRad));double SunDeclinDeg = FMath::RadiansToDegrees(SunDeclinRad);double VarY = FMath::Pow(FMath::Tan(ObliqCorrRad / 2.0), 2.0);// Get the equation of timedouble EqOfTimeMinutes = 4.0 * FMath::RadiansToDegrees(VarY * FMath::Sin(2.0 * GeomMeanLongSunRad) - 2.0 * EccentEarthOrbit * FMath::Sin(GeomMeanAnomSunRad) + 4.0 * EccentEarthOrbit * VarY * FMath::Sin(GeomMeanAnomSunRad) * FMath::Cos(2.0 * GeomMeanLongSunRad) - 0.5 * VarY * VarY * FMath::Sin(4.0 * GeomMeanLongSunRad) - 1.25 * EccentEarthOrbit * EccentEarthOrbit * FMath::Sin(2.0 * GeomMeanAnomSunRad));// Get the hour angle of the sunrisedouble HASunriseDeg = FMath::RadiansToDegrees(FMath::Acos(FMath::Cos(FMath::DegreesToRadians(90.833)) / (FMath::Cos(LatitudeRad) * FMath::Cos(SunDeclinRad)) - FMath::Tan(LatitudeRad) * FMath::Tan(SunDeclinRad)));//	double SunlightDurationMinutes = 8.0 * HASunriseDeg;// Get the local time of the sun's rise and setdouble SolarNoonLST = (720.0 - 4.0 * Longitude - EqOfTimeMinutes + TimeOffset * 60.0) / 1440.0;double SunriseTimeLST = SolarNoonLST - HASunriseDeg * 4.0 / 1440.0;double SunsetTimeLST = SolarNoonLST + HASunriseDeg * 4.0 / 1440.0;// Get the true solar timedouble TrueSolarTimeMinutes = FMath::Fmod(CalcTime.GetTimeOfDay().GetTotalMinutes() + EqOfTimeMinutes + 4.0 * Longitude - 60.0 * TimeOffset, 1440.0);// Get the hour angle of current timedouble HourAngleDeg = TrueSolarTimeMinutes < 0 ? TrueSolarTimeMinutes / 4.0 + 180 : TrueSolarTimeMinutes / 4.0 - 180.0;double HourAngleRad = FMath::DegreesToRadians(HourAngleDeg);// Get the solar zenith angledouble SolarZenithAngleRad = FMath::Acos(FMath::Sin(LatitudeRad) * FMath::Sin(SunDeclinRad) + FMath::Cos(LatitudeRad) * FMath::Cos(SunDeclinRad) * FMath::Cos(HourAngleRad));double SolarZenithAngleDeg = FMath::RadiansToDegrees(SolarZenithAngleRad);// Get the sun elevationdouble SolarElevationAngleDeg = 90.0 - SolarZenithAngleDeg;double SolarElevationAngleRad = FMath::DegreesToRadians(SolarElevationAngleDeg);double TanOfSolarElevationAngle = FMath::Tan(SolarElevationAngleRad);// Get the approximated atmospheric refractiondouble ApproxAtmosphericRefractionDeg = 0.0;if (SolarElevationAngleDeg <= 85.0){if (SolarElevationAngleDeg > 5.0){ApproxAtmosphericRefractionDeg = 58.1 / TanOfSolarElevationAngle - 0.07 / FMath::Pow(TanOfSolarElevationAngle, 3) + 0.000086 / FMath::Pow(TanOfSolarElevationAngle, 5) / 3600.0;}else{if (SolarElevationAngleDeg > -0.575){ApproxAtmosphericRefractionDeg = 1735.0 + SolarElevationAngleDeg * (-518.2 + SolarElevationAngleDeg * (103.4 + SolarElevationAngleDeg * (-12.79 + SolarElevationAngleDeg * 0.711)));}else{ApproxAtmosphericRefractionDeg = -20.772 / TanOfSolarElevationAngle;}}ApproxAtmosphericRefractionDeg /= 3600.0;}// Get the corrected solar elevationdouble SolarElevationcorrectedforatmrefractionDeg = SolarElevationAngleDeg + ApproxAtmosphericRefractionDeg;// Get the solar azimuth double tmp = FMath::RadiansToDegrees(FMath::Acos(((FMath::Sin(LatitudeRad) * FMath::Cos(SolarZenithAngleRad)) - FMath::Sin(SunDeclinRad)) / (FMath::Cos(LatitudeRad) * FMath::Sin(SolarZenithAngleRad))));double SolarAzimuthAngleDegcwfromN = HourAngleDeg > 0.0 ? FMath::Fmod(tmp + 180.0, 360.0) : FMath::Fmod(540.0 - tmp, 360.0);// offset elevation angle to fit with UE coords systemSunPositionData.Elevation = 180.0f + SolarElevationAngleDeg;SunPositionData.CorrectedElevation = 180.0f + SolarElevationcorrectedforatmrefractionDeg;SunPositionData.Azimuth = SolarAzimuthAngleDegcwfromN;SunPositionData.SolarNoon = FTimespan::FromDays(SolarNoonLST);SunPositionData.SunriseTime = FTimespan::FromDays(SunriseTimeLST);SunPositionData.SunsetTime = FTimespan::FromDays(SunsetTimeLST);
}

参考