De/Serialization for wavefront object files

Adds to export/import topology as wavefront object files. This enables users to view/edit/use topology inside 3rd party 3D editors

ff/Serialize.cpp

+//  ************************************************************************************************
+//
+//  BornAgain: simulate and fit reflection and scattering
+//
+//! @file      ff/Serialize.cpp
+//! @brief     Implements serializing and deserializing of topologies.
+//!
+//! @homepage  https://jugit.fz-juelich.de/mlz/libformfactor
+//! @license   GNU General Public License v3 or higher (see COPYING)
+//! @copyright Forschungszentrum Jülich GmbH 2022
+//! @authors   Scientific Computing Group at MLZ (see CITATION, AUTHORS)
+//
+//  ************************************************************************************************
+
+#include "ff/Serialize.h"
+#include <fstream>
+namespace {
+
+std::string parse_topology_as_wavefront_obj(const ff::PolyhedralTopology& topology,
+                                            const std::vector<R3> vertices)
+{
+    std::stringstream stream;
+    stream << "o 1"
+           << "\n";
+    for (auto vertice : vertices) {
+        stream << "v"
+               << " " << vertice.x() << " " << vertice.y() << " " << vertice.z() << "\n";
+    }
+    stream << "usemtl Default\n";
+
+    for (auto& poly : topology.faces) {
+        if (poly.vertexIndices.size() == 0)
+            continue;
+        stream << "f"
+               << " ";
+        for (size_t i = 0; i < poly.vertexIndices.size(); i++) {
+            stream << poly.vertexIndices[i] + 1;
+            stream << (i == poly.vertexIndices.size() - 1 ? "\n" : " ");
+        }
+    }
+    return stream.str();
+}
+
+std::pair<ff::PolyhedralTopology, std::vector<R3>> parse_string_as_wavefront_obj(std::string data)
+{
+    std::vector<R3> vertices;
+    ff::PolyhedralTopology topology;
+    std::string line;
+    std::stringstream datastream(data);
+    while (std::getline(datastream, line)) {
+        std::istringstream is(line);
+        if (line.at(0) == 'v' && line.at(1) == ' ') {
+            std::string data;
+            std::string tp;
+            double x, y, z;
+            std::getline(is, data, ' ');
+            is >> x >> y >> z;
+            vertices.push_back(R3(x, y, z));
+        }
+        if (line.at(0) == 'f') {
+            std::string data;
+            std::string tp;
+            std::string a, b, c;
+            std::vector<std::string> seglist;
+            std::vector<int> intlist;
+            while (std::getline(is, data, ' ')) {
+                seglist.push_back(data);
+            }
+            seglist.erase(seglist.begin());
+            for (auto seg : seglist) {
+                auto i = std::stoi(seg.substr(0, seg.find("/"))) - 1;
+                intlist.push_back(i);
+            }
+            topology.faces.push_back({intlist, false});
+        }
+    }
+    return {topology, vertices};
+}
+
+} // namespace
+
+namespace ff::io {
+
+void export_ff_to_obj(std::string fileName, const PolyhedralTopology& topology,
+                      const std::vector<R3> vertices)
+{
+    std::ofstream myfile;
+    myfile.open(fileName);
+    myfile << parse_topology_as_wavefront_obj(topology, vertices);
+    myfile.close();
+}
+
+std::pair<PolyhedralTopology, std::vector<R3>> import_obj_to_ff(std::string fileName)
+{
+    std::pair<PolyhedralTopology, std::vector<R3>> tp;
+    std::ifstream file;
+    file.open(fileName);
+    tp = parse_string_as_wavefront_obj(
+        std::string((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>()));
+    file.close();
+    return tp;
+}
+
+} // namespace ff::io