add Midpoint uniform subdivision scheme

src/OpenMesh/Tools/Subdivider/Uniform/MidpointT.hh

+#pragma once
+
+#include <OpenMesh/Core/Mesh/BaseKernel.hh>
+#include <OpenMesh/Tools/Subdivider/Uniform/SubdividerT.hh>
+#include <OpenMesh/Core/Utils/PropertyManager.hh>
+
+#include <algorithm>
+
+namespace OpenMesh {
+namespace Subdivider {
+namespace Uniform {
+
+template<typename MeshType, typename RealType = double>
+class MidpointT : public SubdividerT<MeshType, RealType>
+{
+public:
+    using real_t = RealType;
+    using mesh_t = MeshType;
+    using parent_t = SubdividerT<MeshType, RealType>;
+
+    using parent_t::parent_t;
+
+    const char* name() const { return "midpoint"; }
+
+protected: // SubdividerT interface
+    bool prepare(mesh_t& _m) override
+    {
+        return true;
+    }
+
+    bool subdivide(mesh_t& _m, size_t _n, const bool _update_points = true) override
+    {
+        auto edge_midpoint = makePropertyManagerFromNew<EPropHandleT<typename mesh_t::VertexHandle>>(_m, "edge_midpoint");
+        auto is_original_vertex = makePropertyManagerFromNew<VPropHandleT<bool>>(_m, "is_original_vertex");
+
+        for (size_t iteration = 0; iteration < _n; ++iteration) {
+            is_original_vertex.set_range(_m.vertices_begin(), _m.vertices_end(), true);
+            // Create vertices on edge midpoints
+            for (const auto& eh : _m.edges()) {
+                auto new_vh = _m.new_vertex(_m.calc_edge_midpoint(eh));
+                edge_midpoint[eh] = new_vh;
+                is_original_vertex[new_vh] = false;
+            }
+            // Create new faces from original faces
+            for (const auto& fh : _m.faces()) {
+                std::vector<typename mesh_t::VertexHandle> new_corners;
+                for (const auto& eh : _m.fe_range(fh)) {
+                    new_corners.push_back(edge_midpoint[eh]);
+                }
+                _m.add_face(new_corners);
+            }
+            // Create new faces from original vertices
+            for (const auto& vh : _m.vertices()) {
+                if (is_original_vertex[vh]) {
+                    if (!_m.is_boundary(vh)) {
+                        std::vector<typename mesh_t::VertexHandle> new_corners;
+                        for (const auto& eh : _m.ve_range(vh)) {
+                            new_corners.push_back(edge_midpoint[eh]);
+                        }
+                        std::reverse(begin(new_corners), end(new_corners));
+                        _m.add_face(new_corners);
+                    }
+                }
+            }
+            for (const auto& vh : _m.vertices()) {
+                if (is_original_vertex[vh]) {
+                    _m.delete_vertex(vh);
+                }
+            }
+        }
+        return true;
+    }
+
+    bool cleanup(mesh_t& _m) override
+    {
+        return true;
+    }
+};
+
+} // namespace Uniform
+} // namespace Subdivider
+} // namespace OpenMesh