geant4/source/geometry/magneticfield/include/G4TCachedMagneticField.hh

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// G4TCachedMagneticField

// Author: Josh Xie (CERN, Google Summer of Code 2014), June 2014
// Supervisors:  Sandro Wenzel, John Apostolakis (CERN)
// --------------------------------------------------------------------
#ifndef G4TCACHED_MAGNETIC_FIELD_HH
#define G4TCACHED_MAGNETIC_FIELD_HH

#include "G4Types.hh"
#include "G4ThreeVector.hh"
#include "G4MagneticField.hh"

/**
 * @brief G4TCachedMagneticField is a templated implementation for a specialisation
 * of G4MagneticField used to cache the Magnetic Field value.
 */

template <class T_Field>
class G4TCachedMagneticField : public G4MagneticField
{
  public:

    G4TCachedMagneticField(T_Field* pTField, G4double distance)
      : G4MagneticField()
      , fLastLocation(DBL_MAX, DBL_MAX, DBL_MAX)
      , fLastValue(DBL_MAX, DBL_MAX, DBL_MAX)
      , fCountCalls(0)
      , fCountEvaluations(0)
    {
      fpMagneticField = pTField;
      fDistanceConst  = distance;

      this->ClearCounts();
    }

    virtual ~G4TCachedMagneticField() = default;

    G4TCachedMagneticField(const G4TCachedMagneticField<T_Field>& rightCMF)
    {
      fpMagneticField = rightCMF.fpMagneticField;
      fDistanceConst  = rightCMF.fDistanceConst;
      fLastLocation   = rightCMF.fLastLocation;
      fLastValue      = rightCMF.fLastValue;
      this->ClearCounts();
    }

    G4TCachedMagneticField& operator=(const G4TCachedMagneticField& right)
    {
      if(&right == this) { return *this; }

      fpMagneticField = right.fpMagneticField;

      fDistanceConst= right.fDistanceConst;
      fLastLocation = right.fLastLocation;
      fLastValue = right.fLastValue;

      fCountCalls = 0;
      fCountEvaluations = 0;
    
      return *this;
    }

    G4TCachedMagneticField* Clone() const
    {
      G4cout << "Clone is called" << G4endl;
      // Cannot use copy constructor: I need to clone associated magnetic field
      T_Field* aF = this->fpMagneticField->T_Field::Clone();
      G4TCachedMagneticField* cloned = new G4TCachedMagneticField(aF, this->fDistanceConst);
      cloned->fLastLocation = this->fLastLocation;
      cloned->fLastValue    = this->fLastValue;
      return cloned;
    }

    void ReportStatistics()
    {
      G4cout << " Cached field: " << G4endl
             << "   Number of calls:        " << fCountCalls << G4endl
             << "   Number of evaluations : " << fCountEvaluations << G4endl;
    }

    virtual void GetFieldValue(const G4double Point[4], G4double* Bfield) const
    {
      G4ThreeVector newLocation(Point[0], Point[1], Point[2]);

      G4double distSq = (newLocation - fLastLocation).mag2();
      fCountCalls++;
      if(distSq < fDistanceConst * fDistanceConst)
      {
        Bfield[0] = fLastValue.x();
        Bfield[1] = fLastValue.y();
        Bfield[2] = fLastValue.z();
      }
      else
      {
        fpMagneticField->T_Field::GetFieldValue(Point, Bfield);
        fCountEvaluations++;
        fLastLocation = G4ThreeVector(Point[0], Point[1], Point[2]);
        fLastValue = G4ThreeVector(Bfield[0], Bfield[1], Bfield[2]);
      }
    }

    G4double GetConstDistance() const { return fDistanceConst; }
    void SetConstDistance(G4double dist) { fDistanceConst = dist; }

    G4int GetCountCalls() const { return fCountCalls; }
    G4int GetCountEvaluations() const { return fCountEvaluations; }
    void ClearCounts()
    {
      fCountCalls       = 0;
      fCountEvaluations = 0;
    }

  protected:

    mutable G4int fCountCalls, fCountEvaluations;

  private:

    T_Field* fpMagneticField;

    /** When the field is evaluated within this distance it will not change. */
    G4double fDistanceConst;

    /** Caching state. */
    mutable G4ThreeVector fLastLocation;
    mutable G4ThreeVector fLastValue;
};

#endif