gsd.cc

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// gemc
#include "gsd.h"
 
// geant4
#include "G4SDManager.hh"
 
// Thread-local sensitive detector instance.
// Constructor: initializes base logging, Geant4 SD name, and the hits collection name used for this detector.
GSensitiveDetector::GSensitiveDetector(const std::string&               sdName,
                                       const std::shared_ptr<GOptions>& goptions) :
    GBase(goptions, GSENSITIVE_LOGGER),
    G4VSensitiveDetector(sdName) {
    log->info(2, FUNCTION_NAME, " for " + sdName);
 
    // collectionName is a G4VSensitiveDetector G4CollectionNameVector.
    // GEMC uses its own handling of hits; this is set primarily for compatibility with Geant4 conventions/examples.
    std::string hitCollectionName = sdName + "__HitCollection";
    collectionName.insert(hitCollectionName);
 
    log->debug(CONSTRUCTOR, FUNCTION_NAME, " for " + sdName);
}
 
 
// Thread-local; called at the beginning of each event.
// Allocates and registers the per-event hits collection and resets per-event caches.
void GSensitiveDetector::Initialize(G4HCofThisEvent* g4hc) {
    std::string sdName = GetName();
    log->info(1, FUNCTION_NAME, sdName);
 
    // Hit content definition is read once per event from the digitization routine.
    gHitBitSet = digitization_routine->readoutSpecs->getHitBitSet();
 
    // Clearing touchableVector at the start of the event (per-event hit identity cache).
    touchableVector.clear();
 
    // Initializing gHitsCollection using the Geant4 G4THitsCollection constructor (expects detector and collection names).
    gHitsCollection = new GHitsCollection(sdName, collectionName[0]);
 
    // Add hits collection to the Geant4 event container.
    // hcID is assigned by Geant4 and can be retrieved later by collection name.
    auto hcID = G4SDManager::GetSDMpointer()->GetCollectionID(collectionName[0]);
    g4hc->AddHitsCollection(hcID, gHitsCollection);
 
    log->info(2, "Added collection id ", hcID, " to G4HCofThisEvent");
}
 
 
// Thread-local; called for each step in sensitive volumes.
// Applies plugin filtering and touchable transformation, then creates new hits or updates existing hits.
G4bool GSensitiveDetector::ProcessHits(G4Step* thisStep, [[maybe_unused]] G4TouchableHistory* g4th) {
    // If there is a decision to skip this hit based on deposited energy, return immediately.
 
    double depe = thisStep->GetTotalEnergyDeposit();
 
    if (digitization_routine->decisionToSkipHit(depe)) { return true; }
 
    // The hits collection should have been created in Initialize().
    if (gHitsCollection == nullptr) { log->error(ERR_NOCOLLECTION, "No hit collection found"); }
 
    // Get the vector of processed touchables returned by the digitization routine.
    // If not overridden by the plugin, the base implementation typically returns a vector with the input touchable only.
    std::vector<std::shared_ptr<GTouchable>> thisStepProcessedTouchables =
        digitization_routine->processTouchable(getGTouchable(thisStep), thisStep);
 
    auto hcsize = gHitsCollection->GetSize();
 
    log->info(2, FUNCTION_NAME, " for ", GetName(),
              " with ", std::to_string(thisStepProcessedTouchables.size()), " touchable(s), edep: ",
              std::to_string(depe), ", Hit collection size: ", hcsize);
 
    // If a new touchable is created, create a new GHit.
    // Otherwise, retrieve the existing hit and append step information according to gHitBitSet.
    for (auto thisGTouchable : thisStepProcessedTouchables) {
        // Track id is attached to the touchable to keep hit identity consistent across updates.
        thisGTouchable->assignTrackId(thisStep->GetTrack()->GetTrackID());
        thisGTouchable->assignPId(thisStep->GetTrack()->GetDefinition()->GetPDGEncoding());
 
        if (isThisANewTouchable(thisGTouchable)) {
            // New hit: constructor fills initial step information based on gHitBitSet.
            gHitsCollection->insert(new GHit(thisGTouchable, gHitBitSet, thisStep));
        }
        else {
            // Existing hit: locate it and add additional information from this step according to gHitBitSet.
            GHit* existingHit = getHitInHitCollectionUsingTouchable(thisGTouchable);
            if (existingHit != nullptr) {
                existingHit->addHitInfosForBitset(gHitBitSet, thisStep);
            }
        }
    }
 
    return true;
}
 
 
// Checks whether a touchable has already been seen in this event.
// If not present, it is appended to the per-event cache.
bool GSensitiveDetector::isThisANewTouchable(const std::shared_ptr<GTouchable>& thisTouchable) {
    log->info(2, "GSensitiveDetector::isThisANewTouchable for " + GetName(),
              " with touchable: " + thisTouchable->getIdentityString());
 
    if (thisTouchable->exists_in_vector(touchableVector)) {
        log->info(2, " ❌ not a new GTouchable, it is found, retrieving hit...");
        return false; // Not a new touchable.
    }
    else {
        log->info(2, " ✅ yes, new GTouchable. Adding it to touchableVector.");
        touchableVector.push_back(*thisTouchable);
        return true; // It's a new touchable.
    }
}
 
 
// Linear search for the hit matching the provided touchable.
// The collection is expected to contain a matching entry when called from ProcessHits().
GHit* GSensitiveDetector::getHitInHitCollectionUsingTouchable(const std::shared_ptr<GTouchable>& gtouchable) {
    for (unsigned int i = 0; i < gHitsCollection->GetSize(); i++) {
        GHit*                              thisHit           = (*gHitsCollection)[i];
        const std::shared_ptr<GTouchable>& thisHitGTouchable = thisHit->getGTouchable();
 
        if (*gtouchable == *thisHitGTouchable) {
            log->info(2, "GSensitiveDetector::getHitInHitCollectionUsingTouchable for " + GetName() +
                      " found existing hit in collection for touchable: " + gtouchable->getIdentityString() +
                      " at index: " + std::to_string(i));
            return thisHit;
        }
    }
 
    log->error(ERR_HITNOTFOUNDINCOLLECTION,
               "GHit not found in hit collection for touchable: " + gtouchable->getIdentityString(),
               "in ", GetName());
}
 
 
// Thread-local end-of-event hook.
// At this stage, Geant4 owns the event hit container that references the hits collection.
void GSensitiveDetector::EndOfEvent([[maybe_unused]] G4HCofThisEvent* g4hc) {
    log->info(1, "GSensitiveDetector::EndOfEvent for " + GetName());
}