buildSolid.cc

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// gemc
#include "gutilities.h"
 
// g4system
#include "cadSystemFactory.h"
 
// ───────────────── CADMesh single-header library ────────────────
// https://github.com/christopherpoole/CADMesh
//
// *Modifications applied to the vendor header:*
//   - Marked the following classes `final`
//       • BuiltInReader
//       • TessellatedMesh
//   - Reason: https://devblogs.microsoft.com/oldnewthing/20200619-00/?p=103877
//
// *Optional Dependencies*
// Define `USE_CADMESH_ASSIMP_READER` **before** including `CADMesh.hh`
// to enable Assimp-based file loading.
//
// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
// !!! SET THIS BEFORE INCLUDING CADMESH.HH TO USE THE ASSIMP READER
// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
#define USE_CADMESH_ASSIMP_READER
// If you want Assimp to be the default reader, uncomment:
// #define CADMESH_DEFAULT_READER ASSIMP
 
#include "CADMesh.hh"
 
// Geant4 units
#include "CLHEP/Units/SystemOfUnits.h"
 
G4VSolid* G4CadSystemFactory::buildSolid(const GVolume* s,
                                         std::unordered_map<std::string,
                                                            G4Volume*>* g4s) {
    std::string g4name = s->getG4Name();
 
    // Dependency check: solids can require other solids (copy/boolean operations).
    if (!checkSolidDependencies(s, g4s)) return nullptr;
 
    // Locate or allocate the wrapper used to cache solid/logical/physical pointers.
    auto thisG4Volume = getOrCreateG4Volume(g4name, g4s);
    if (thisG4Volume->getSolid() != nullptr) return thisG4Volume->getSolid();
 
    // CAD file handling:
    // - file path is stored in the volume "description" field
    // - extension determines which CADMesh reader path is used
    std::string fileName   = s->getDescription(); // full file path from DB
    G4String    g4filename = fileName;
 
    // File extension (last token after '.').
    std::string extension =
        gutilities::getStringVectorFromStringWithDelimiter(fileName, ".").back();
 
    // PLY / STL via CADMesh & Assimp reader.
    if (extension == "ply" || extension == "stl") {
        auto mesh = CADMesh::TessellatedMesh::From(g4filename,
                                                   CADMesh::File::ASSIMP());
 
        // Optional uniform scale factor, authored per volume in the "scale" YAML attribute and
        // carried through the geometry "parameters" column (CAD solids have no other use for it).
        // It multiplies the millimetre interpretation, e.g. scale=10 reads a mesh drawn in cm.
        double            scale = 1.0;
        const std::string pars  = s->getParameters();
        if (!pars.empty() && pars != "NULL") {
            try { scale = std::stod(pars); }
            catch (const std::exception&) {
                log->warning("G4CadSystemFactory: volume <", g4name,
                             "> has a non-numeric scale <", pars, ">; using 1.0");
            }
        }
 
        // The CAD file is interpreted in millimetres (times the per-volume scale) to match
        // typical detector CAD conventions.
        mesh->SetScale(CLHEP::mm * scale);
 
        // Do not flip vertex winding unless the CAD source requires it.
        mesh->SetReverse(false);
 
        thisG4Volume->setSolid(mesh->GetSolid(), log);
        return thisG4Volume->getSolid();
    }
 
    // Unsupported extension: return nullptr so the caller can decide whether to treat it as fatal.
    log->warning("G4CadSystemFactory: file <", fileName,
                 "> has unsupported extension <", extension, ">");
    return nullptr;
}