```// @(#):\$Name:  \$:\$Id: TGeoHalfSpace.cxx,v 1.10 2006/07/03 16:10:44 brun Exp \$
// Author: Mihaela Gheata   03/08/04

/*************************************************************************
*                                                                       *
* For the licensing terms see \$ROOTSYS/LICENSE.                         *
* For the list of contributors see \$ROOTSYS/README/CREDITS.             *
*************************************************************************/

//_____________________________________________________________________________
// TGeoHalfSpace - A half-space defined by:
//            p[3] - an arbitrary point on the plane
//            n[3] - normal at the plane in point P
//    A half-space is not really a shape, because it is infinite. The normal
//    points "outside" the half-space
//_____________________________________________________________________________

#include "Riostream.h"
#include "TGeoHalfSpace.h"

ClassImp(TGeoHalfSpace)

//_____________________________________________________________________________
TGeoHalfSpace::TGeoHalfSpace()
{
// Dummy constructor
SetShapeBit(TGeoShape::kGeoHalfSpace);
SetShapeBit(TGeoShape::kGeoInvalidShape);
memset(fP, 0, 3*sizeof(Double_t));
memset(fN, 0, 3*sizeof(Double_t));
}

//_____________________________________________________________________________
TGeoHalfSpace::TGeoHalfSpace(const char *name, Double_t *p, Double_t *n)
:TGeoBBox(name, 0,0,0)
{
// Constructor with name, point on the plane and normal
SetShapeBit(TGeoShape::kGeoHalfSpace);
SetShapeBit(TGeoShape::kGeoInvalidShape);
Double_t param[6];
memcpy(param, p, 3*sizeof(Double_t));
memcpy(&param[3], n, 3*sizeof(Double_t));
SetDimensions(param);
}

//_____________________________________________________________________________
TGeoHalfSpace::TGeoHalfSpace(Double_t *param)
:TGeoBBox(0,0,0)
{
// Default constructor specifying minimum and maximum radius
SetShapeBit(TGeoShape::kGeoHalfSpace);
SetShapeBit(TGeoShape::kGeoInvalidShape);
SetDimensions(param);
}

//_____________________________________________________________________________
TGeoHalfSpace::~TGeoHalfSpace()
{
// destructor
}

//_____________________________________________________________________________
void TGeoHalfSpace::ComputeNormal(Double_t * /*point*/, Double_t *dir, Double_t *norm)
{
// Compute normal to closest surface from POINT.
memcpy(norm, fN, 3*sizeof(Double_t));
if (norm[0]*dir[0]+norm[1]*dir[1]+norm[2]*dir[2]<0) {
norm[0] = -norm[0];
norm[1] = -norm[1];
norm[2] = -norm[2];
}
}

//_____________________________________________________________________________
Bool_t TGeoHalfSpace::Contains(Double_t *point) const
{
// test if point is inside the half-space
Double_t r[3];
r[0] = fP[0]-point[0];
r[1] = fP[1]-point[1];
r[2] = fP[2]-point[2];
Double_t rdotn = r[0]*fN[0]+r[1]*fN[1]+r[2]*fN[2];
if (rdotn < 0) return kFALSE;
return kTRUE;
}

//_____________________________________________________________________________
Int_t TGeoHalfSpace::DistancetoPrimitive(Int_t /*px*/, Int_t /*py*/)
{
// A half-space does not have a mesh primitive
return 999;
}

//_____________________________________________________________________________
Double_t TGeoHalfSpace::DistFromInside(Double_t *point, Double_t *dir, Int_t iact, Double_t step, Double_t *safe) const
{
// compute distance from inside point to the plane
Double_t r[3];
r[0] = fP[0]-point[0];
r[1] = fP[1]-point[1];
r[2] = fP[2]-point[2];
Double_t rdotn = r[0]*fN[0]+r[1]*fN[1]+r[2]*fN[2];
if (iact<3 && safe) {
*safe = rdotn;
if (iact==0) return TGeoShape::Big();
if ((iact==1) && (*safe>step)) return TGeoShape::Big();
}
// compute distance to plane
Double_t snxt = TGeoShape::Big();
Double_t ddotn = dir[0]*fN[0]+dir[1]*fN[1]+dir[2]*fN[2];
if (ddotn==0) return snxt;
snxt = rdotn/ddotn;
if (snxt<0) return TGeoShape::Big();
return snxt;
}

//_____________________________________________________________________________
Double_t TGeoHalfSpace::DistFromOutside(Double_t *point, Double_t *dir, Int_t iact, Double_t step, Double_t *safe) const
{
// compute distance from inside point to the plane
Double_t r[3];
r[0] = fP[0]-point[0];
r[1] = fP[1]-point[1];
r[2] = fP[2]-point[2];
Double_t rdotn = r[0]*fN[0]+r[1]*fN[1]+r[2]*fN[2];
if (iact<3 && safe) {
*safe = -rdotn;
if (iact==0) return TGeoShape::Big();
if ((iact==1) && (step<*safe)) return TGeoShape::Big();
}
// compute distance to plane
Double_t snxt = TGeoShape::Big();
Double_t ddotn = dir[0]*fN[0]+dir[1]*fN[1]+dir[2]*fN[2];
if (ddotn==0) return snxt;
snxt = rdotn/ddotn;
if (snxt<0) return TGeoShape::Big();
return snxt;
}

//_____________________________________________________________________________
TGeoVolume *TGeoHalfSpace::Divide(TGeoVolume * /*voldiv*/, const char * /*divname*/, Int_t /*iaxis*/, Int_t /*ndiv*/,
Double_t /*start*/, Double_t /*step*/)
{
// Divide the shape along one axis.
Error("Divide", "Half-spaces cannot be divided");
return 0;
}

//_____________________________________________________________________________
void TGeoHalfSpace::InspectShape() const
{
// print shape parameters
printf("*** Shape %s: TGeoHalfSpace ***\n", GetName());
printf("    Point    : %11.5f, %11.5f, %11.5f\n", fP[0], fP[1], fP[2]);
printf("    Normal   : %11.5f, %11.5f, %11.5f\n", fN[0], fN[1], fN[2]);
}

//_____________________________________________________________________________
Double_t TGeoHalfSpace::Safety(Double_t *point, Bool_t /*in*/) const
{
// computes the closest distance from given point to this shape, according
// to option. The matching point on the shape is stored in spoint.
Double_t r[3];
r[0] = fP[0]-point[0];
r[1] = fP[1]-point[1];
r[2] = fP[2]-point[2];
Double_t rdotn = r[0]*fN[0]+r[1]*fN[1]+r[2]*fN[2];
return TMath::Abs(rdotn);
}

//_____________________________________________________________________________
void TGeoHalfSpace::SavePrimitive(ostream &out, Option_t * /*option*/ /*= ""*/)
{
// Save a primitive as a C++ statement(s) on output stream "out".
if (TObject::TestBit(kGeoSavePrimitive)) return;
out << "   // Shape: " << GetName() << " type: " << ClassName() << endl;
out << "   point[0] = " << fP[0] << ";" << endl;
out << "   point[1] = " << fP[1] << ";" << endl;
out << "   point[2] = " << fP[2] << ";" << endl;
out << "   norm[0]  = " << fN[0] << ";" << endl;
out << "   norm[1]  = " << fN[1] << ";" << endl;
out << "   norm[2]  = " << fN[2] << ";" << endl;
out << "   TGeoShape *" << GetPointerName() << " = new TGeoHalfSpace(\"" << GetName() << "\", point,norm);" << endl;
TObject::SetBit(TGeoShape::kGeoSavePrimitive);
}

//_____________________________________________________________________________
void TGeoHalfSpace::SetDimensions(Double_t *param)
{
// Set half-space parameters as stored in an array.
memcpy(fP, param, 3*sizeof(Double_t));
memcpy(fN, &param[3], 3*sizeof(Double_t));
Double_t nsq = TMath::Sqrt(fN[0]*fN[0]+fN[1]*fN[1]+fN[2]*fN[2]);
fN[0] /= nsq;
fN[1] /= nsq;
fN[2] /= nsq;
}
```

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