feat: add obj drawing possibility as python function (#2400)

Title says it all, since Obj is a natural visualisation of the Core library that doesn't need any extension, it's also handy from the python side.

This practically allows you to do
```python
acts.drawSurfacesObj(surfaces, context, colouring, filename)
```

Examples/Python/CMakeLists.txt

@@ -19,6 +19,7 @@ pybind11_add_module(ActsPythonBindings
   src/Input.cpp
   src/Propagation.cpp
   src/Generators.cpp
+  src/Obj.cpp
   src/TruthTracking.cpp
   src/TrackFitting.cpp
   src/TrackFinding.cpp

Examples/Python/src/ModuleEntry.cpp

@@ -150,6 +150,7 @@ void addHepMC3(Context& ctx);
 void addExaTrkXTrackFinding(Context& ctx);
 void addEDM4hep(Context& ctx);
 void addSvg(Context& ctx);
+void addObj(Context& ctx);
 void addOnnx(Context& ctx);
 void addOnnxMlpack(Context& ctx);
 void addOnnxNeuralCalibrator(Context& ctx);
@@ -399,6 +400,7 @@ PYBIND11_MODULE(ActsPythonBindings, m) {
   addHepMC3(ctx);
   addExaTrkXTrackFinding(ctx);
   addEDM4hep(ctx);
+  addObj(ctx);
   addSvg(ctx);
   addOnnx(ctx);
   addOnnxMlpack(ctx);

Examples/Python/src/Obj.cpp

@@ -0,0 +1,55 @@
+// This file is part of the Acts project.
+//
+// Copyright (C) 2023 CERN for the benefit of the Acts project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <Acts/Definitions/Algebra.hpp>
+#include <Acts/Geometry/GeometryContext.hpp>
+#include <Acts/Plugins/Python/Utilities.hpp>
+#include <Acts/Surfaces/Surface.hpp>
+#include <Acts/Visualization/GeometryView3D.hpp>
+#include <Acts/Visualization/ObjVisualization3D.hpp>
+#include <Acts/Visualization/ViewConfig.hpp>
+
+#include <memory>
+
+#include <pybind11/pybind11.h>
+#include <pybind11/stl.h>
+
+namespace py = pybind11;
+using namespace pybind11::literals;
+
+using namespace Acts;
+
+namespace Acts::Python {
+void addObj(Context& ctx) {
+  auto [m, mex] = ctx.get("main", "examples");
+
+  {
+    /// Write a collection of surfaces to an '.obj' file
+    ///
+    /// @param surfaces is the collection of surfaces
+    /// @param viewContext is the geometry context
+    /// @param viewRgb is the color of the surfaces
+    /// @param fileName is the path to the output file
+    ///
+    mex.def("writeSurfacesObj",
+            [](const std::vector<std::shared_ptr<Surface>>& surfaces,
+               const GeometryContext& viewContext,
+               const std::array<int, 3>& viewRgb, const std::string& fileName) {
+              Acts::ViewConfig sConfig = Acts::ViewConfig{viewRgb};
+              Acts::GeometryView3D view3D;
+              Acts::ObjVisualization3D obj;
+
+              for (const auto& surface : surfaces) {
+                view3D.drawSurface(obj, *surface, viewContext,
+                                   Acts::Transform3::Identity(), sConfig);
+              }
+              obj.write(fileName);
+            });
+  }
+}
+}  // namespace Acts::Python