#define DEGREE_IN_RADIANS 0.0174532925
#define EARTH_AXIAL_TILT 23.5			//earth axial tilt in degrees
#define EARTH_ORBITAL_PERIOD 365.25		//earth orbital period in days (length of a year)
#define EARTH_ROTATION_PERIOD 24.0		//earth rotation period in hours (length of a day)
#define LOCATION_TIME_SPRING_EQUINOX 81.0	//day number of the year when day and night cycle is exactly 12/12 hours
#define LOCATION_LATITUDE 48.0			//latitude of current location

void set_sun_position(var day_,var hour_,var minute_,var second_,var latitude_,var spring_equinox_)
{
	double B=(360.0/EARTH_ORBITAL_PERIOD) * (day_-spring_equinox_);

	//Equation of Time (EoT)
	double EoT=9.87*sin(2*B*DEGREE_IN_RADIANS) - 7.53*cos(B*DEGREE_IN_RADIANS) - 1.5*sin(B*DEGREE_IN_RADIANS);

	//Time Correction Factor (TC)
	double TC=EoT;

	//Local Time (LT)
	double LT=hour_ + (minute_/60.0) + (second_/3600.0);

	//Local Solar Time (LST)
	double LST=LT + TC/60.0;

	//Hour Angle (HRA)
	double HRA=15.0 * (LST - 12.0);

	//Number of days since the start of the year (d)
	double d=day_ + LT/24.0;

	//Declination (D)
	double D=EARTH_AXIAL_TILT * sin((360.0/EARTH_ORBITAL_PERIOD) * (d - spring_equinox_) * DEGREE_IN_RADIANS);

	//Sun Elevation (sun_angle.tilt)
	double sun_angle_tilt_sin=cos(HRA*DEGREE_IN_RADIANS)*cos(D*DEGREE_IN_RADIANS)*cos(LOCATION_LATITUDE*DEGREE_IN_RADIANS)+sin(D*DEGREE_IN_RADIANS)*sin(LOCATION_LATITUDE*DEGREE_IN_RADIANS);
	if(sun_angle_tilt_sin < -1){sun_angle_tilt_sin=-1;}
	if(sun_angle_tilt_sin > 1){sun_angle_tilt_sin=1;}		
	double sun_angle_tilt=asin(sun_angle_tilt_sin)/DEGREE_IN_RADIANS;

	//Sun Azimuth (sun_angle.pan)
	double sun_angle_pan_cos=(sin(D*DEGREE_IN_RADIANS)-sin(sun_angle_tilt*DEGREE_IN_RADIANS)*sin(LOCATION_LATITUDE*DEGREE_IN_RADIANS))/(cos(sun_angle_tilt*DEGREE_IN_RADIANS)*cos(LOCATION_LATITUDE*DEGREE_IN_RADIANS));
	if(sun_angle_pan_cos < -1){sun_angle_pan_cos=-1;}
	if(sun_angle_pan_cos > 1){sun_angle_pan_cos=1;}		
	double sun_angle_pan=acos(sun_angle_pan_cos)/DEGREE_IN_RADIANS;
	if(LST>12.0 && HRA>0.0){sun_angle_pan=360.0-sun_angle_pan;}
	sun_angle_pan=cycle(sun_angle_pan,0,360);
		
	sun_angle.pan=sun_angle_pan;
	sun_angle.tilt=sun_angle_tilt;
}

//set sun position to day 181 (june 30th) at time 14:30:00 (2:30 P.M.)
set_sun_position(181,14,30,0,LOCATION_LATITUDE,LOCATION_TIME_SPRING_EQUINOX);

var day= 0;
var hour = 0;
var minute = 0;
	
while(1) {
		
	minute++;
	if (minute == 60) {
		minute = 0;
		hour++;
		if (hour == 25) {
			hour = 0;
			day++;
			if (day == 366) {
				day = 0;
			}
		}
	}
		
set_sun_position(day,hour,minute,0,LOCATION_LATITUDE,LOCATION_TIME_SPRING_EQUINOX);
	wait(1);
}

var second_=0;
var minute_=0;
var hour_=12;
var time_speed_=0.5;
var day_=120; //april 30th

while(1)
{
	second_+=time_speed_*time_step;
	if(second_>=60)
	{
		minute_+=integer(second_/60);
		second_=fraction(second_/60);
		
		if(minute_>=60)
		{
			hour_+=integer(minute_/60);
			minute_=fraction(minute_/60);
			
			hour_%=24;
		}
	}
	
	set_sun_position(day_,hour_,minute_,second_,LOCATION_LATITUDE,LOCATION_TIME_SPRING_EQUINOX);
	
	wait(1);
}

hour_+=integer(minute_/60);

while(1){
	DEBUG_VAR(second_, 10);
	DEBUG_VAR(minute_, 50);
	DEBUG_VAR(hour_, 100);
	second_ += time_speed_*time_step;
		
	if(second_ >= 60)
	{
		second_ = fraction(second_ / 60);
		minute_ += 1;
			
		if(minute_ >= 60)
		{
			minute_ = fraction(minute_ / 60);
			hour_+= 1;				
			hour_ %= 24;
		}
	}
		
	set_sun_position(day_, hour_, minute_, second_, LOCATION_LATITUDE, LOCATION_TIME_SPRING_EQUINOX);
		
	wait(1);
}

#define EARTH_AXIAL_TILT 23.5	//earth axial tilt in degrees
#define EARTH_ORBITAL_PERIOD 365.25	//earth orbital period in days (length of a year)
#define EARTH_ROTATION_PERIOD 24.0	//earth rotation period in hours (length of a day)
#define LOCATION_TIME_SPRING_EQUINOX 81	//day number of the year when day and night cycle is exactly 12/12 hours
#define LOCATION_LATITUDE 48		//latitude of current location

void set_sun_position(var day_,var hour_,var minute_,var second_,var latitude_,var spring_equinox_)
{
	var B=(360/EARTH_ORBITAL_PERIOD) * (day_-spring_equinox_);
	
	//Equation of Time (EoT)
	var EoT=9.87*sinv(2*B) - 7.53*cosv(B) - 1.5*sinv(B);
	
	//Time Correction Factor (TC)
	var TC=EoT;
	
	//Local Time (LT)
	var LT=hour_ + (minute_/60.0) + (second_/3600.0);
	
	//Local Solar Time (LST)
	var LST=LT + TC/60;
	
	//Hour Angle (HRA)
	var HRA=15 * (LST - 12);
	
	//Number of days since the start of the year (d)
	var d=day_ + LT/24;
	
	//Declination (D)
	var D=EARTH_AXIAL_TILT * sinv((360/EARTH_ORBITAL_PERIOD) * (d - spring_equinox_));
	
	//Sun Elevation (sun_angle.tilt)
	sun_angle.tilt=asinv((cosv(HRA) * cosv(D) * cosv(latitude_)) + (sinv(D) * sinv(latitude_)));
	
	//Sun Azimuth (sun_angle.pan)
	sun_angle.pan=acosv( (sinv(D) - sinv(sun_angle.tilt) * sinv(latitude_)) / (cosv(sun_angle.tilt) * cosv(latitude_)) );
	if(LST>12 && HRA >0){sun_angle.pan=360-sun_angle.pan;}
}

void main(){
	shadow_stencil = 2;
	
	level_load("");
	
	ENTITY* ground = ent_create(CUBE_MDL, vector(0, 0, 0), NULL);
	vec_set(ground.scale_x, vector(100, 100, 1));
	
	ENTITY* ball = ent_create(SPHERE_MDL, vector(random(20), random(20), 150), NULL);
	set(ball, SHADOW);
	
	vec_set(camera.x, vector(-1436, 0, 897));
	vec_set(camera.pan, vector(0, -36, 0));
	
	var second_ = 0;
	var minute_ = 0;
	var hour_ = 10;
	var time_speed_ = 150;
	var day_ = 120; // april 30th

	while(1)
	{
		DEBUG_VAR(second_, 10);
		DEBUG_VAR(minute_, 50);
		DEBUG_VAR(hour_, 100);
		second_ += time_speed_*time_step;
		
		if(second_ >= 60)
		{
			second_ = fraction(second_ / 60);
			minute_ += 1;
			
			if(minute_ >= 60)
			{
				minute_ = fraction(minute_ / 60);
				hour_+= 1;				
				hour_ %= 24;
			}
		}
		
		set_sun_position(day_, hour_, minute_, second_, LOCATION_LATITUDE, LOCATION_TIME_SPRING_EQUINOX);
		
		wait(1);
	}	
}