Add conversion of Geant4 transforms and basic solids to ORANGE (#1169)

src/geocel/g4vg/Scaler.hh

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <utility>
+#include <G4ThreeVector.hh>
 #include <G4TwoVector.hh>
 
 #include "geocel/detail/LengthUnits.hh"

src/geocel/g4vg/SolidConverter.cc

@@ -105,7 +105,7 @@ namespace
 [[maybe_unused]] auto calculate_theta_phi(G4ThreeVector const& axis)
     -> std::pair<double, double>
 {
-    // The components of the symmetry axis for G4Para/Trap are alway encoded
+    // The components of the symmetry axis for G4Para/Trap are always encoded
     // as a vector (A.tan(theta)cos(phi), A.tan(theta)sin(phi), A).
     double const tan_theta_cos_phi = axis.x() / axis.z();
     double const tan_theta_sin_phi = axis.y() / axis.z();

src/orange/CMakeLists.txt

@@ -82,6 +82,20 @@ if(CELERITAS_USE_JSON)
   list(APPEND PRIVATE_DEPS nlohmann_json::nlohmann_json)
 endif()
 
+if(CELERITAS_USE_Geant4 AND CELERITAS_REAL_TYPE STREQUAL "double")
+  set( _cg4org_sources
+    g4org/SolidConverter.cc
+  )
+  celeritas_get_g4libs(_cg4org_libs geometry)
+  list(APPEND _cg4org_libs Celeritas::corecel Celeritas::geocel)
+
+  celeritas_add_object_library(geocel_g4org ${_cg4org_sources})
+  celeritas_target_link_libraries(geocel_g4org PRIVATE ${_cg4org_libs})
+
+  list(APPEND SOURCES $<TARGET_OBJECTS:geocel_g4org>)
+  list(APPEND PRIVATE_DEPS geocel_g4org)
+endif()
+
 #-----------------------------------------------------------------------------#
 # Create library
 #-----------------------------------------------------------------------------#

src/orange/g4org/Scaler.hh

@@ -0,0 +1,65 @@
+//----------------------------------*-C++-*----------------------------------//
+// Copyright 2023-2024 UT-Battelle, LLC, and other Celeritas developers.
+// See the top-level COPYRIGHT file for details.
+// SPDX-License-Identifier: (Apache-2.0 OR MIT)
+//---------------------------------------------------------------------------//
+//! \file orange/g4org/Scaler.hh
+//---------------------------------------------------------------------------//
+#pragma once
+
+#include <utility>
+#include <G4ThreeVector.hh>
+#include <G4TwoVector.hh>
+
+#include "corecel/Assert.hh"
+#include "corecel/cont/Array.hh"
+#include "geocel/detail/LengthUnits.hh"
+
+namespace celeritas
+{
+namespace g4org
+{
+//---------------------------------------------------------------------------//
+/*!
+ * Convert a unit from Geant4 scale to another.
+ *
+ * The input is the length scale of the original input in the new units.
+ */
+class Scaler
+{
+  public:
+    //! Default scale to CLHEP units (mm)
+    Scaler() : scale_{celeritas::lengthunits::millimeter} {}
+
+    //! Scale with an explicit factor, probably for testing
+    explicit Scaler(double sc) : scale_{sc} { CELER_EXPECT(scale_ > 0); }
+
+    //! Multiply a value by the scale
+    double operator()(double val) const { return val * scale_; }
+
+    //! Convert and scale a 2D point
+    Array<double, 2> operator()(G4TwoVector const& vec) const
+    {
+        return this->to<Array<double, 2>>(vec.x(), vec.y());
+    }
+
+    //! Convert and scale a 3D point
+    Array<double, 3> operator()(G4ThreeVector const& vec) const
+    {
+        return this->to<Array<double, 3>>(vec.x(), vec.y(), vec.z());
+    }
+
+    //! Create an array or other object by scaling each argument
+    template<class S, class... Ts>
+    S to(Ts&&... args) const
+    {
+        return S{(*this)(std::forward<Ts>(args))...};
+    }
+
+  private:
+    double scale_;
+};
+
+//---------------------------------------------------------------------------//
+}  // namespace g4org
+}  // namespace celeritas