Geant4 API
===========
Review `G4UserXXXAction` API with eye to external optical photon
propagation (a la Chroma).
Chroma grabs and kills optical photons tracks
in `G4UserTrackingAction::PreUserTrackingAction` and seemingly doesnt give them back.
G4EventManager Overview
------------------------
* http://www.tunl.duke.edu/~tajima/geant4/pdf/jun2009b/1/kernel.pdf
* An event is the basic unit of simulation in Geant4.
* At beginning of processing, primary tracks are generated. These primary tracks are pushed into a stack.
* A track is popped up from the stack one by one and tracked. Resulting secondary tracks are pushed into the stack.
* This tracking lasts as long as the stack has a track.
* When the stack becomes empty, processing of one event is over.
Optional User Actions
-------------------------
* http://geant4.web.cern.ch/geant4/G4UsersDocuments/UsersGuides/ForApplicationDeveloper/html/UserActions/OptionalActions.html
G4EventManager::DoProcessing
------------------------------
::
098 void G4EventManager::DoProcessing(G4Event* anEvent)
...
139 trackContainer->PrepareNewEvent();
...
145 sdManager = G4SDManager::GetSDMpointerIfExist();
146 if(sdManager)
147 { currentEvent->SetHCofThisEvent(sdManager->PrepareNewEvent()); }
148
149 if(userEventAction) userEventAction->BeginOfEventAction(currentEvent);
...
171 G4VTrajectory* previousTrajectory;
172 while( ( track = trackContainer->PopNextTrack(&previousTrajectory) ) != 0 )
173 {
...
184 tracking = true;
185 trackManager->ProcessOneTrack( track );
186 istop = track->GetTrackStatus();
187 tracking = false;
...
217 G4TrackVector * secondaries = trackManager->GimmeSecondaries();
218 switch (istop)
219 {
220 case fStopButAlive:
221 case fSuspend:
222 trackContainer->PushOneTrack( track, aTrajectory );
223 StackTracks( secondaries );
224 break;
225
226 case fPostponeToNextEvent:
227 trackContainer->PushOneTrack( track );
228 StackTracks( secondaries );
229 break;
230
231 case fStopAndKill:
232 StackTracks( secondaries );
233 delete track;
234 break;
235
236 case fAlive:
237 G4cout << "Illeagal TrackStatus returned from G4TrackingManager!"
238 << G4endl;
239 case fKillTrackAndSecondaries:
240 //if( secondaries ) secondaries->clearAndDestroy();
241 if( secondaries )
242 {
243 for(size_t i=0;i<secondaries->size();i++)
244 { delete (*secondaries)[i]; }
245 secondaries->clear();
246 }
247 delete track;
248 break;
249 }
250 }
G4UserEventAction
-------------------
G4UserStackingAction
---------------------
`ClassifyNewTrack()`
~~~~~~~~~~~~~~~~~~~~~~
* invoked by G4StackManager whenever a new G4Track object is "pushed" onto a stack by G4EventManager
* returns an enumerator, G4ClassificationOfNewTrack with one of four possible values:
* fUrgent - track is placed in the urgent stack
* fWaiting - track is placed in the waiting stack, and will not be simulated until the urgent stack is empty
* fPostpone - track is postponed to the next event
* fKill - the track is deleted immediately and not stored in any stack.
`NewStage()`
~~~~~~~~~~~~~
Invoked when the urgent stack is empty and the waiting stack contains at least one G4Track object.
Here the user may kill or re-assign to different stacks all the tracks in the
waiting stack by calling the `stackManager->ReClassify()` method which, in turn,
calls the `ClassifyNewTrack()` method.
If no user action is taken, all tracks in the waiting stack are transferred to the urgent stack.
The user may also decide to abort the current event even though some tracks may remain in the waiting
stack by calling `stackManager->clear()`.
This method is valid and safe only if it is called from the G4UserStackingAction class.
`PrepareNewEvent()`
~~~~~~~~~~~~~~~~~~~~~
Invoked at the beginning of each event. At this point no primary particles
have been converted to tracks, so the urgent and waiting stacks are empty.
However, there may be tracks in the postponed-to-next-event stack; for each of
these the `ClassifyNewTrack()` method is called and the track is assigned to the
appropriate stack.
Examples DsFastMuonStackAction, DsOpStackAction, ExampleN04
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
::
[blyth@cms01 src]$ vi /data/env/local/dyb/trunk/NuWa-trunk/dybgaudi/Simulation/DetSim/src/DsFastMuonStackAction.cc
* http://dayabay.bnl.gov/dox/DetSim/html/DsOpStackAction_8cc_source.html
G4UserTrackingAction
---------------------
G4UserSteppingAction
---------------------
G4SDManager
------------
* http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/html/ch04s04.html
* http://www.ge.infn.it/geant4/training/portland/readout.pdf
ProcessHits
~~~~~~~~~~~~
::
[blyth@cms01 src]$ grep ProcessHits *.cc
DsPmtSensDet.cc:bool DsPmtSensDet::ProcessHits(G4Step* step,
DsPmtSensDet.cc: error() << "ProcessHits: step has no or empty touchable history" << endreq;
DsRpcSensDet.cc:bool DsRpcSensDet::ProcessHits(G4Step* step,
DsRpcSensDet.cc: error() << "ProcessHits: step has no or empty touchable history."
[blyth@cms01 src]$
Registering hits on sensitive detectors
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Maybe possible lookahead to the next step with `fStep->GetPostStepPoint()->GetSensitiveDetector()`
to see if about to hit.
Whats the Chroma equivalent of SD "Collision detection"
::
42 42 117: G4StepStatus G4SteppingManager::Stepping()
. . 118: //////////////////////////////////////////
. . 119: {
. . 120:
. . 121: //--------
. . 122: // Prelude
. . 123: //--------
. . 124: #ifdef G4VERBOSE
. . 125: // !!!!! Verbose
10 10 126: if(verboseLevel>0) fVerbose->NewStep();
. . 127: else
13 13 128: if(verboseLevel==-1) {
. . 129: G4VSteppingVerbose::SetSilent(1);
. . 130: }
. . 131: else
9 246 132: G4VSteppingVerbose::SetSilent(0);
. . 133: #endif
. . 134:
. . 135: // Store last PostStepPoint to PreStepPoint, and swap current and nex
. . 136: // volume information of G4Track. Reset total energy deposit in one Step.
169 1759 137: fStep->CopyPostToPreStepPoint();
265 317 138: fStep->ResetTotalEnergyDeposit();
. . 139:
. . 140: // Switch next touchable in track to current one
390 9025 141: fTrack->SetTouchableHandle(fTrack->GetNextTouchableHandle());
...
...
...
. . 218: //-------
. . 219: // Finale
. . 220: //-------
. . 221:
. . 222: // Update 'TrackLength' and remeber the Step length of the current Step
69 144 223: fTrack->AddTrackLength(fStep->GetStepLength());
85 91 224: fPreviousStepSize = fStep->GetStepLength();
21 36 225: fStep->SetTrack(fTrack);
. . 226: #ifdef G4VERBOSE
. . 227: // !!!!! Verbose
. . 228:
108 108 229: if(verboseLevel>0) fVerbose->StepInfo();
. . 230: #endif
. . 231: // Send G4Step information to Hit/Dig if the volume is sensitive
270 2794 232: fCurrentVolume = fStep->GetPreStepPoint()->GetPhysicalVolume();
288 296 233: StepControlFlag = fStep->GetControlFlag();
29 29 234: if( fCurrentVolume != 0 && StepControlFlag != AvoidHitInvocation) {
. . 235: fSensitive = fStep->GetPreStepPoint()->
258 278 236: GetSensitiveDetector();
26 26 237: if( fSensitive != 0 ) {
1 4325 238: fSensitive->Hit(fStep);
. . 239: }
. . 240: }