VecGeomG4NavigatorBase.h

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// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
// All rights not expressly granted are reserved.
//
// This software is distributed under the terms of the GNU General Public
// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
//
// In applying this license CERN does not waive the privileges and immunities
// granted to it by virtue of its status as an Intergovernmental Organization
// or submit itself to any jurisdiction.
 
#ifndef O2_SIMSETUP_VECGEOMG4NAVIGATORBASE_H_
#define O2_SIMSETUP_VECGEOMG4NAVIGATORBASE_H_
 
#include "VecGeomG4Map.h"
 
#include "G4Navigator.hh"
#include "G4SystemOfUnits.hh"
#include "G4ThreeVector.hh"
 
#include <VecGeom/base/Transformation3D.h>
#include <VecGeom/base/Vector3D.h>
#include <VecGeom/navigation/NavigationState.h>
#include <VecGeom/volumes/PlacedVolume.h>
 
namespace o2::simsetup
{
 
class VecGeomG4NavigatorBase : public G4Navigator
{
 protected:
  using V3 = vecgeom::Vector3D<double>;
  static constexpr double kG4ToVG = 1. / CLHEP::cm;
  static constexpr double kVGToG4 = CLHEP::cm;
 
  explicit VecGeomG4NavigatorBase(VecGeomG4Map const& map) : mMap(map) {}
 
  static V3 toVG(const G4ThreeVector& p) { return {p.x() * kG4ToVG, p.y() * kG4ToVG, p.z() * kG4ToVG}; }
  static V3 toDir(const G4ThreeVector& d) { return {d.x(), d.y(), d.z()}; }
 
  G4VPhysicalVolume* historyFromState(vecgeom::NavigationState const& state);
 
  bool stateFromHistory(vecgeom::NavigationState& state) const;
 
  [[gnu::always_inline]] static bool directionLeaves(const V3& n, const V3& dir)
  {
    constexpr double kMinExitingNormalCosine = 1e-3; // as in G4NormalNavigation
    return n.Dot(dir) >= kMinExitingNormalCosine;
  }
 
  [[gnu::always_inline]] static bool directionLeaves(vecgeom::NavigationState const& exited, const V3& point,
                                                     const V3& dir)
  {
    if (exited.IsOutside() || exited.Top() == nullptr) {
      return false;
    }
    vecgeom::Transformation3D m;
    exited.TopMatrix(m);
    V3 n;
    exited.Top()->GetUnplacedVolume()->Normal(m.Transform(point), n);
    if (!(n.Mag2() > 0.5)) {
      return false; // no valid exit normal: Geant4 does not block either
    }
    return directionLeaves(m.InverseTransformDirection(n), dir);
  }
 
  VecGeomG4Map const& mMap;
};
 
} // namespace o2::simsetup
 
#endif