MMPrimaryGeneratorAction.cpp

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// This file is part of the Acts project.
//
// Copyright (C) 2017 CERN for the benefit of the Acts project
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

#include "ACTFW/Plugins/Geant4/MMPrimaryGeneratorAction.hpp"

#include <stdexcept>

#include "G4Event.hh"
#include "G4ParticleDefinition.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4RandomDirection.hh"
#include "G4UnitsTable.hh"
#include "Randomize.hh"

FW::Geant4::MMPrimaryGeneratorAction*
    FW::Geant4::MMPrimaryGeneratorAction::fgInstance = nullptr;

FW::Geant4::MMPrimaryGeneratorAction::MMPrimaryGeneratorAction(
    const G4String& particleName, G4double energy, G4int randomSeed1,
    G4int randomSeed2)
    : G4VUserPrimaryGeneratorAction(), fParticleGun(nullptr) {
  // configure the run
  if (fgInstance) {
    throw std::logic_error("Attempted to duplicate a singleton");
  } else {
    fgInstance = this;
  }
  G4int nofParticles = 1;
  fParticleGun = std::make_unique<G4ParticleGun>(nofParticles);

  // default particle kinematic
  G4ParticleTable* particleTable = G4ParticleTable::GetParticleTable();
  G4ParticleDefinition* particle = particleTable->FindParticle(particleName);
  fParticleGun->SetParticleDefinition(particle);
  fParticleGun->SetParticleEnergy(energy);
  G4UnitDefinition::PrintUnitsTable();

  // set the random seeds
  CLHEP::HepRandom::getTheEngine()->setSeed(randomSeed1, randomSeed2);
}

FW::Geant4::MMPrimaryGeneratorAction::~MMPrimaryGeneratorAction() {
  fgInstance = nullptr;
}

FW::Geant4::MMPrimaryGeneratorAction*
FW::Geant4::MMPrimaryGeneratorAction::Instance() {
  // Static acces function via G4RunManager
  return fgInstance;
}

void FW::Geant4::MMPrimaryGeneratorAction::GeneratePrimaries(G4Event* anEvent) {
  // this function is called at the begining of event
  G4double phi = -M_PI + G4UniformRand() * 2. * M_PI;
  G4double theta = G4UniformRand() * M_PI;
  // build a direction
  m_direction =
      G4ThreeVector(cos(phi) * sin(theta), sin(phi) * sin(theta), cos(theta));
  m_position = G4ThreeVector(
      0., 0., 0.);  
  // set to the particle gun and
  fParticleGun->SetParticleMomentumDirection(m_direction);
  fParticleGun->SetParticlePosition(m_position);

  fParticleGun->GeneratePrimaryVertex(anEvent);
}