openmesh - impl - Remove Duplicated Vertices

openmesh - impl - Remove Duplicated Vertices

关于openmesh元素删除实现的介绍参见：openmesh - src - trimesh delete and add elements - grassofsky - 博客园 (cnblogs.com)

重复点删除的主要步骤如下：

• 找到所有的重复顶点，并设定每组重复顶点中需要保留的顶点；
• 记录这些重复顶点对应的三角形；（因为下一步在顶点删除的时候，会将顶点周围关联的三角形都删除，并将顶点的状态设置为deleted）；
• 删除所有的重复的顶点；（此时会删除关联的三角形和半边）；
• 可能出现孤立点，删除孤立点；（此步骤可选）；
• 回收，边和面的资源；（此步骤为了后续添加关联面做准备）；
• 遍历所有的重复顶点关联的三角形，如果这个三角形中仅含有一个重复点，那么添加该三角形，并将重复点替换为对应的保留的点；
• 恢复重新添加的保留的顶点的删除状态；
• 资源回收；

具体实现代码如下：

#include <iostream>
#include <OpenMesh/Core/Mesh/TriMesh_ArrayKernelT.hh>
#include <OpenMesh/Tools/Utils/Timer.hh>

#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
#include "doctest.h"

using namespace OpenMesh;

struct MyTraits : public OpenMesh::DefaultTraits
{
#if 1
  typedef OpenMesh::Vec3f Point;
  typedef OpenMesh::Vec3f Normal;
#else
  typedef OpenMesh::Vec3d Point;
  typedef OpenMesh::Vec3d Normal;
#endif
};

typedef OpenMesh::TriMesh_ArrayKernelT<MyTraits>  TriMesh;


//-----------------------------------------------------------------------------

bool HasDuplicatedVertex(const TriMesh& mesh)
{
    std::map<TriMesh::Point, int> mapPoints;
    for (auto iter = mesh.vertices_begin(); iter != mesh.vertices_end(); ++iter)
    {
        auto iterPt = mapPoints.find(mesh.point(*iter));
        if (iterPt == mapPoints.end())
        {
            mapPoints.insert_or_assign(mesh.point(*iter), 1);
        }
        else
        {
            return true;
        }
    }

    return false;
}

int RemoveDuplicatedVertex(TriMesh& mesh)
{
    // Find all duplicated vertices
    int iOriginalNumVertices = static_cast<int>(mesh.n_vertices());
    std::map<TriMesh::Point, TriMesh::VertexHandle> mapPoints;
    std::map<TriMesh::VertexHandle, std::set<TriMesh::VertexHandle>> mapDuplicatedVertices;

    for (auto iter = mesh.vertices_begin(); iter != mesh.vertices_end(); ++iter)
    {
        auto& pt = mesh.point(*iter);
        if (mapPoints.find(pt) != mapPoints.end())
        {
            auto& vh = mapPoints[pt];
            auto iterDuplicatedVertices = mapDuplicatedVertices.find(vh);
            if (iterDuplicatedVertices == mapDuplicatedVertices.end())
            {
                mapDuplicatedVertices.insert(std::make_pair(vh, std::set<TriMesh::VertexHandle>{ vh, *iter }));
            }
            else
            {
                iterDuplicatedVertices->second.insert(*iter);
            }
        }
        else
        {
            mapPoints.insert(std::make_pair(pt, *iter));
        }
    }

    // Record the duplicated vertices related faces
    std::map<TriMesh::VertexHandle, std::set<std::array<TriMesh::VertexHandle, 3>>> mapVertexFaces;
    for (auto iter = mapDuplicatedVertices.begin(); iter != mapDuplicatedVertices.end(); ++iter)
    {
        auto pair = mapVertexFaces.insert(std::make_pair(iter->first, std::set<std::array<TriMesh::VertexHandle, 3>>{}));
        auto& vecFaces = pair.first->second;
        for (auto v_it = iter->second.begin(); v_it != iter->second.end(); ++v_it)
        {
            for (auto vf_it = mesh.vf_iter(*v_it); vf_it.is_valid(); ++vf_it)
            {
                std::array<TriMesh::VertexHandle, 3> face;
                int i = 0;
                auto fv_it = mesh.fv_begin(*vf_it);
                face[i++] = *(fv_it++);
                face[i++] = *(fv_it++);
                face[i++] = *(fv_it++);
                vecFaces.insert(face);
            }
        }
    }

    if (!mesh.has_vertex_status()) mesh.request_vertex_status();
    if (!mesh.has_face_status())   mesh.request_face_status();
    if (!mesh.has_edge_status())   mesh.request_edge_status();

    // remove all duplicated vertices
    for (auto iter = mapDuplicatedVertices.begin(); iter != mapDuplicatedVertices.end(); ++iter)
    {
        for (auto v_it = iter->second.begin(); v_it != iter->second.end(); ++v_it)
        {
            mesh.delete_vertex(*v_it);
        }
    }

    mesh.delete_isolated_vertices();

    // garbage_collection edge and face
    mesh.garbage_collection(false, true, true);

    // add not degenereated faces
    std::set<TriMesh::VertexHandle> setRemainVertices;
    for (auto iter = mapVertexFaces.begin(); iter != mapVertexFaces.end(); ++iter)
    {
        for (auto f_it = iter->second.begin(); f_it != iter->second.end(); ++f_it)
        {
            std::array<TriMesh::VertexHandle, 3> face = *f_it;
            unsigned short result = 0;
            for (auto iter = mapDuplicatedVertices.begin(); iter != mapDuplicatedVertices.end(); ++iter)
            {
                // bit pos records if the vertex is duplicated vertex or not
                result = 0;
                result |= (iter->second.count(face[0]) == 0 ? 0 : 1);
                result |= (iter->second.count(face[1]) == 0 ? 0 : 2);
                result |= (iter->second.count(face[2]) == 0 ? 0 : 4);
                if (result == 1 || result == 2 || result == 4)
                {
                    // replace the duplicated vertex as remaining vertex
                    face[result / 2] = iter->first;
                    mesh.add_face(face[0], face[1], face[2]);
                    setRemainVertices.insert(face[0]);
                    setRemainVertices.insert(face[1]);
                    setRemainVertices.insert(face[2]);
                    break;
                }
            }
        }
    }

    // recover status of remain vertex
    for (auto v_it = setRemainVertices.begin(); v_it != setRemainVertices.end(); ++v_it)
    {
        mesh.status(*v_it).set_deleted(false);
    }

    // garbage_collection vertex
    mesh.garbage_collection();

    if (!mesh.has_vertex_status()) mesh.release_vertex_status();
    if (!mesh.has_face_status())   mesh.release_vertex_status();
    if (!mesh.has_edge_status())   mesh.release_vertex_status();

    return iOriginalNumVertices - static_cast<int>(mesh.n_vertices());
}

//-----------------------------------------------------------------------------


TEST_CASE("testing delete duplicated vertex")
{
    TriMesh mesh;
    // Add some vertices
    TriMesh::VertexHandle vhandle[7];
    vhandle[0] = mesh.add_vertex(TriMesh::Point(0, 0, 0));
    vhandle[1] = mesh.add_vertex(TriMesh::Point(0, 2, 0));
    vhandle[2] = mesh.add_vertex(TriMesh::Point(2, 2, 0));
    vhandle[3] = mesh.add_vertex(TriMesh::Point(2, 0, 0));
    vhandle[4] = mesh.add_vertex(TriMesh::Point(1, 1, 0));
    vhandle[5] = mesh.add_vertex(TriMesh::Point(1, 1, 0));
    vhandle[6] = mesh.add_vertex(TriMesh::Point(1, 1, 0));

    // Add faces
    mesh.add_face(vhandle[0], vhandle[1], vhandle[4]);
    mesh.add_face(vhandle[0], vhandle[4], vhandle[6]);
    mesh.add_face(vhandle[0], vhandle[6], vhandle[3]);
    mesh.add_face(vhandle[1], vhandle[5], vhandle[4]);
    mesh.add_face(vhandle[1], vhandle[2], vhandle[5]);
    mesh.add_face(vhandle[2], vhandle[6], vhandle[5]);
    mesh.add_face(vhandle[2], vhandle[3], vhandle[6]);
    mesh.add_face(vhandle[4], vhandle[5], vhandle[6]);

    auto iNDeleted = RemoveDuplicatedVertex(mesh);
    CHECK(iNDeleted == 2);
    CHECK(mesh.n_faces() == 4);
    CHECK(mesh.n_vertices() == 5);
    CHECK_FALSE(HasDuplicatedVertex(mesh));
}

其中test case对应的图如下：

其中，顶点v4，v5，v6是重复点。此处绘制的时候，将其分离开来是为了方便观察对应的拓扑结构。