[io] introduce gmsh format backend

frackit/io/CMakeLists.txt

 install(FILES
 brepwriter.hh
+gmshbackend.hh
 gmshwriter.hh
 DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/frackit/io)

frackit/io/gmshbackend.hh

+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+/*****************************************************************************
+ *   See the file COPYING for full copying permissions.                      *
+ *                                                                           *
+ *   This program is free software: you can redistribute it and/or modify    *
+ *   it under the terms of the GNU General Public License as published by    *
+ *   the Free Software Foundation, either version 3 of the License, or       *
+ *   (at your option) any later version.                                     *
+ *                                                                           *
+ *   This program is distributed in the hope that it will be useful,         *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of          *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the            *
+ *   GNU General Public License for more details.                            *
+ *                                                                           *
+ *   You should have received a copy of the GNU General Public License       *
+ *   along with this program.  If not, see <http://www.gnu.org/licenses/>.   *
+ *****************************************************************************/
+/*!
+ * \file
+ * \ingroup IO
+ * \brief Backend for Gmsh Syntax, depending on the desired .geo file format version.
+ */
+#ifndef FRACKIT_GMSH_FORMAT_BACKEND_HH
+#define FRACKIT_GMSH_FORMAT_BACKEND_HH
+
+#include <string>
+#include <cassert>
+#include <type_traits>
+
+namespace Frackit::Gmsh {
+
+/*!
+ * \ingroup IO
+ * \brief Backend for writing Gmsh Syntax to files,
+ *        depending on the desired .geo file format version.
+ */
+class GmshFormatBackend
+{
+
+public:
+
+    /*!
+     * \brief Default constructor.
+     */
+    GmshFormatBackend()
+    {
+        setVersion(4, 0);
+    }
+
+    /*!
+     * \brief Constructor defining the gmsh version
+     *        for which a .geo file is to be written.
+     * \param majVersion major gmsh version
+     * \param minVersion minor gmsh version
+     */
+    GmshFormatBackend(int maj, int min)
+    {
+        setVersion(maj, min);
+    }
+
+    /*!
+     * \brief Update version settings.
+     */
+    void setVersion(int maj, int min)
+    {
+        // we use two-digits minor version
+        if (min < 10) min *= 10;
+
+        assert(min < 100);
+        gmshVersion_ = maj*100 + min;
+        assert(gmshVersion_ < 1000);
+    }
+
+    /*!
+     * \brief Write a physical entity definition.
+     * \param geoFile The geoFile to write to
+     * \param entityDimension Entity dimension
+     * \param physicalId The id to give the physical entity
+     * \param elementaryIds Ids of the elementary entities composing the physical entity
+     */
+    template<class IdList>
+    void writePhysicalGeometry(std::ofstream& geoFile,
+                               int entityDimension,
+                               std::size_t physicalId,
+                               const IdList& elementaryIds) const
+    {
+        static_assert(std::is_integral_v<typename IdList::value_type>,
+                      "Ids must be integral types");
+
+        const auto& geomKey = getGeometryKeyword_(entityDimension);
+        geoFile << "Physical " << geomKey << "(" << physicalId << ") = ";
+        writeIdList_(geoFile, elementaryIds);
+        geoFile << ";\n";
+    }
+
+    /*!
+     * \brief Write variable definition.
+     * \param geoFile The geoFile to write to
+     * \param varName variable name
+     * \param varValue variable value
+     */
+    template<class ValueType>
+    void writeVariableDefinition(std::ofstream& geoFile,
+                                 const std::string& varName,
+                                 const ValueType& varValue) const
+    {
+        geoFile << varName << " = " << varValue << ";\n";
+    }
+
+    /*!
+     * \brief Write mesh size definition.
+     * \param geoFile The geoFile to write to
+     * \param entityDimension Dimension of the entity on which to set the mesh size.
+     * \param elementaryIds List of elementary entity ids (must correspond
+     *                      to entities with dimension entityDimension)
+     * \param size string containing the size or size variable name.
+     */
+    template<class IdList>
+    void writeMeshSizeDefinition(std::ofstream& geoFile,
+                                 int entityDimension,
+                                 const IdList& idList,
+                                 const std::string& size) const
+    {
+        const auto& meshSizeKey = getMeshSizeKeyword_();
+        const auto& geomKey = getGeometryKeyword_(entityDimension);
+        geoFile << meshSizeKey << "{ PointsOf{" << geomKey;
+        writeIdList_(geoFile, idList);
+        geoFile << ";} } = " << size << ";\n";
+    }
+
+private:
+    template<class IdList>
+    void writeIdList_(std::ofstream& geoFile, const IdList& idList) const
+    {
+        geoFile << "{";
+        geoFile << idList[0];
+        for (unsigned int j = 1; j < idList.size(); ++j)
+            geoFile << ", " << idList[j];
+        geoFile << "}";
+    }
+
+    std::string getGeometryKeyword_(unsigned int geomDim) const
+    {
+        assert(geomDim <= 3);
+        static const std::vector<std::string> keywords = {
+            "Point", "Curve", "Surface", "Volume"
+        };
+
+        return keywords[geomDim];
+    }
+
+    std::string getMeshSizeKeyword_() const
+    {
+        if (gmshVersion_ < 470)
+            return "Characteristic Length";
+        return "MeshSize";
+    }
+
+    int gmshVersion_;
+};
+
+} // end namespace Frackit::Gmsh
+
+#endif // FRACKIT_GMSH_BACKEND_HH