Add vertices and faces to the Mesh

[czc98]

Hi!
Is there an easy way to add new vertices and faces to the Mesh?
For example, fill holes, the new face will have some vertices from the old Mesh as well as some new vertices.

[czc98]

I found the addPart method, but after merging two Meshes, the identical vertex parts are not merged.

[Fedr]

Hi,

Is there an easy way to add new vertices and faces to the Mesh?
For example, fill holes, the new face will have some vertices from the old Mesh as well as some new vertices.

Actually, there are many different ways of accomplishing it. You can look at our fill hole implementation, for example.

As to high-level function, please consider addTriangles from MRMeshBuilder.h:

// adds triangles in the existing topology, given face indecies must be free;
// settings.region on output contain the remaining triangles that could not be added into the topology right now, but may be added later when other triangles appear in the mesh
MRMESH_API void addTriangles( MeshTopology & res, const Triangulation & t, const BuildSettings & settings = {} );

// adds triangles in the existing topology, auto selecting face ids for them;
// vertTriples on output contain the remaining triangles that could not be added into the topology right now, but may be added later when other triangles appear in the mesh
MRMESH_API void addTriangles( MeshTopology & res, std::vector<VertId> & vertTriples,
    FaceBitSet * createdFaces = nullptr ); //< this set receives indices of added triangles

These functions allows one to add triangles to existing mesh topology, properly connecting them with existing triangles, if they share common vertices. And vertex coordinates can be set directly in mesh.points.

I found the addPart method, but after merging two Meshes, the identical vertex parts are not merged.

Mesh::addPart is another option. Indeed it adds new triangles always as new connected components not joined with existing triangles in the mesh. For the latter task there is another method:

/// this version has more parameters:
///   if flipOrientation then every from triangle is inverted before adding
MRMESH_API void Mesh::addPartByMask( const Mesh & from, const FaceBitSet & fromFaces, bool flipOrientation = false,
    const std::vector<EdgePath> & thisContours = {}, // contours on this mesh that have to be stitched with
    const std::vector<EdgePath> & fromContours = {}, // contours on from mesh during addition
    // optionally returns mappings: from.id -> this.id
    const PartMapping & map = {} );

It joins new triangles with existing triangles along common edges given in "contour"-arguments.

[Fedr]

In general mesh class can store vertex and face elements that are not actually present in mesh, e.g. if they were deleted previously. MeshTopology::hasFace and MeshTopology::hasVert return false for such elements. mesh.pack() optimizes memory storage of a mesh leaving only active elements in it, so MeshTopology::hasFace and MeshTopology::hasVert return only true after mesh.pack().

[Grantim]

Could you also provide real data to reproduce the issue? i. g. mesh and all side data that you use?

[czc98]

I modified my code and got the desired effect.

Eigen::VectorXi vertIdInMesh(V2_3d.rows());
for (int i = 0, len = V2_3d.rows(); i < len; i++)
{
    if (VM2(i, 0) == 0 || VM2(i, 0) == -2)
    {
        // change
        vertIdInMesh(i) = mesh.addPoint(MR::Vector3f(V2_3d(i, 0), V2_3d(i, 1), V2_3d(i, 2))).get();
    }
    else
    {
        if (VM2(i, 0) == -1)
        {
            vertIdInMesh(i) = 0;
        }
        else
        {
            vertIdInMesh(i) = VM2(i, 0);
        }
    }
}
MR::Triangulation new_tris;
for (int i = 0, len = F2.rows(); i < len; i++)
{
    Eigen::RowVector3i face = F2.row(i);
    new_tris.push_back(MR::ThreeVertIds({MR::VertId(vertIdInMesh(face(0))), MR::VertId(vertIdInMesh(face(1))), MR::VertId(vertIdInMesh(face(2)))}));
}
MR::MeshBuilder::BuildSettings setting;
setting.shiftFaceId = mesh.topology.numValidFaces();
MR::MeshBuilder::addTriangles(mesh.topology, new_tris, setting); // change
mesh.pack();

The code logic hasn't changed, but I still don't know what was wrong with the previous code.
I also have a question as to whether there is an easy way to get the added triangle's FaceBitSet.

[Grantim]

Hello!
Easiest way to get new faces bitset is this:

auto oldFaceBitSet = mesh.topology.getValidFaces();
MR::MeshBuilder::BuildSettings setting;
setting.shiftFaceId = mesh.topology.numValidFaces();
MR::MeshBuilder::addTriangles(mesh.topology, new_tris, setting); // change
auto newFaces = mesh.topology.getValidFaces() - oldFaceBitSet;

// note that pack can change faces order so we need to map FaceBitSet after it
FaceMap packFMap;
mesh.pack( &packFMap );

// map FaceBitSet after packing
FaceBitSet newFacesAfterPack(mesh.topology.getValidFaces().size());
for ( auto of : newFaces )
    if ( auto nf = packFMap[of] )
        newFacesAfterPack.set( nf );

[czc98]

Thanks! I need to consult you again.
Knowing the VertId of a vertex, how to get its 1-ring vertex id. I checked the api but couldn't find the right way

[Fedr]

For iterating over all 1-ring vertex neighbours d of vertex v, please use orgRing function from MeshLib/source/MRMesh/MRRingIterator.h:

for ( auto e : orgRing( mesh.topology, v ) )
{
    assert( mesh.topology.org( e ) == v );
    auto d = mesh.topology.dest( e );
    ...
}

[czc98]

thanks!