/// <summary>
/// Method that determines whether photon reflects or refracts across interface. When this
/// method is called photon is sitting on boundary of region and CurrentRegionIndex is Index
/// of region photon had been in.
/// </summary>
public void CrossRegionOrReflect()
{
double cosTheta = _tissue.GetAngleRelativeToBoundaryNormal(this);
double nCurrent = _tissue.Regions[CurrentRegionIndex].RegionOP.N;
int neighborIndex = _tissue.GetNeighborRegionIndex(this);
double nNext = _tissue.Regions[neighborIndex].RegionOP.N;
double coscrit;
if (nCurrent > nNext)
{
coscrit = Math.Sqrt(1.0 - (nNext / nCurrent) * (nNext / nCurrent));
}
else
{
coscrit = 0.0;
}
double probOfReflecting;
double cosThetaSnell;
// call Fresnel be default to have uZSnell set, used to be within else
probOfReflecting = Optics.Fresnel(nCurrent, nNext, cosTheta, out cosThetaSnell);
if (cosTheta <= coscrit)
{
probOfReflecting = 1.0;
}
//else
// probOfReflecting = Optics.Fresnel(nCurrent, nNext, cosTheta, out cosThetaSnell);
/* Decide whether or not photon goes to next region */
// perform first check so that rng not called on pseudo-collisions
if ((probOfReflecting == 0.0) || (_rng.NextDouble() > probOfReflecting)) // transmitted
{
// if at border of system
if (_tissue.OnDomainBoundary(this.DP.Position) && !_firstTimeEnteringDomain)
{
DP.StateFlag = DP.StateFlag.Add(_tissue.GetPhotonDataPointStateOnExit(DP.Position));
// adjust CAW weight for portion of track prior to exit
if (Absorb == AbsorbContinuous)
{
AbsorbContinuous();
}
CurrentRegionIndex = neighborIndex;
//don't need to update these unless photon not dead upon exiting tissue
//DP.Direction.Ux *= nCurrent / nNext;
//DP.Direction.Uy *= nCurrent / nNext;
//DP.Direction.Uz = uZSnell;
}
else // not on domain boundary, at internal interface or first time enter tissue, pass to next
{
CurrentRegionIndex = neighborIndex;
DP.Direction = _tissue.GetRefractedDirection(DP.Position, DP.Direction,
nCurrent, nNext, cosThetaSnell);
if (_firstTimeEnteringDomain)
{
_firstTimeEnteringDomain = false;
}
}
}
else // don't cross, reflect
{
DP.Direction = _tissue.GetReflectedDirection(DP.Position, DP.Direction);
// check if specular reflection
if (_firstTimeEnteringDomain)
{
DP.StateFlag = DP.StateFlag.Add(PhotonStateType.PseudoSpecularTissueBoundary);
}
}
}
