LlGetSunDirection

Returns a vector that is the direction of the sun in the region.

The sun position can be dynamic or static depending upon the wishes of the sim owner.

This can be used to quickly determine whether it is day or night (in shortened SL days) as the script runs: if the returned vector's Z element is positive, then the sun is above the horizon.

integer lightsOn = -1;//not TRUE or FALSE
 
CheckSun()
{
    vector sun = llGetSunDirection();
    integer turnLightsOn = (sun.z < 0);
    if(turnLightsOn != lightsOn)
    {
        lightsOn = turnLightsOn;
        llSetPrimitiveParams([ PRIM_FULLBRIGHT, ALL_SIDES, lightsOn ]);
    }
}

AVERAGE_SUN_TILT = -.25 * pi
SEASONAL_SUN_TILT = .03 * pi
SUN_NORMALIZED_OFFSET = .45

This is how mSunOffset is calculated:

F64 daily_phase  = DAILY_OMEGA * U64_to_F64(local_time / USEC_PER_SEC);
F32 sun_phase = (F32)fmod(daily_phase, 2.0*F_PI);
sun_hour -= 6.0f;
mSunOffset = HOURS_TO_RADIANS * sun_hour - (0.25f * F_PI) * cosf(HOURS_TO_RADIANS * sun_hour) - sun_phase;
 
//And here's how sun direction is calculated:
 
void LLRegion::calculateSunInfo(
       U64 current_time,
       LLVector3& directionp,
       LLVector3& ang_velocityp,
       F32& sun_phase)
{
   U64 local_time = current_time;
   if(getSunFixed())
   {
       local_time = 0;
   }
     // Sun moves (once a day) about a circle that lies on a tilted plane.
     // The angle of the plane cycles (once a year) a few radians about
     // some average.
     // These are F64's, otherwise we get rounding errors over time
   F64 daily_phase  = DAILY_OMEGA * U64_to_F64(local_time / USEC_PER_SEC) + mSunOffset;
   F64 yearly_phase = YEARLY_OMEGA * U64_to_F64(local_time / USEC_PER_SEC);
   F32 tilt = AVERAGE_SUN_TILT + SEASONAL_SUN_TILT_AMPLITUDE * (F32)sin(yearly_phase);
 
   sun_phase = (F32)fmod(daily_phase, 2.0*F_PI);
     // move sun around a circle
   directionp.setVec((F32)cos(-daily_phase), (F32)sin(-daily_phase), 0.0f);
     //tilt the circle about X-axis (due east)  
   directionp.rotVec(tilt, 1.0f, 0.0f, 0.0f);
 
     // calculate angular velocity (radians per second)
   ang_velocityp.setVec(0.0f, 0.0f, (F32)DAILY_OMEGA);
   ang_velocityp.rotVec((F32)tilt, 1.0f, 0.0f, 0.0f);
 
     // James wanted the night to be shorter than the day.
     // We can do this by offsetting the center of the sun's orbit in the positive
     // z-direction and normalizing the new vector.
   directionp.mV[VZ] += SUN_NORMALIZED_OFFSET;
   F32 R = directionp.normVec();
 
     // We also need to correct the angular velocity
     //
     // V = W % R
     // V has constant magnitude
     // As R goes up, W must go down
     // W and R are always perpendicular
     // ===>
     // W *= 1 / |R|
   ang_velocityp *= 1.0f / R;
}

Source: Zyzzy Zarf

Functions