3362dd5535
git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@1244 fdac6126-5c0c-442c-9429-916003d36597
135 lines
4.3 KiB
Plaintext
135 lines
4.3 KiB
Plaintext
/** \page mesh_operations Some basic operations: Flipping and collapsing edges
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In this section you will learn about some basic operations on a mesh that %OpenMesh
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already provides. Comprising the flipping of edges in a triangle mesh as well as
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collapsing edges by joining the two adjacent vertices.
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\li \ref op_flip
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\li \ref op_collapse
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\section op_flip Flipping edges in triangle meshes
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Considering two adjacent faces of a triangle mesh, there exist exactly two
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different configurations of the inner edge. Calling the function
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OpenMesh::TriConnectivity::flip(EdgeHandle _eh) will flip the specified edge to
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its opposite orientation as shown in the illustration below.
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\image html mesh.flip.png "Flipping edges in a triangle mesh"
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So, the following snippet of code shows how to use this in your applications:
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\code
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TriMesh mesh;
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// Add some vertices
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TriMesh::VertexHandle vhandle[4];
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vhandle[0] = mesh.add_vertex(MyMesh::Point(0, 0, 0));
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vhandle[1] = mesh.add_vertex(MyMesh::Point(0, 1, 0));
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vhandle[2] = mesh.add_vertex(MyMesh::Point(1, 1, 0));
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vhandle[3] = mesh.add_vertex(MyMesh::Point(1, 0, 0));
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// Add two faces
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std::vector<TriMesh::VertexHandle> face_vhandles;
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face_vhandles.push_back(vhandle[2]);
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face_vhandles.push_back(vhandle[1]);
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face_vhandles.push_back(vhandle[0]);
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mesh.add_face(face_vhandles);
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face_vhandles.clear();
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face_vhandles.push_back(vhandle[2]);
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face_vhandles.push_back(vhandle[0]);
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face_vhandles.push_back(vhandle[3]);
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mesh.add_face(face_vhandles);
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// Now the edge adjacent to the two faces connects
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// vertex vhandle[0] and vhandle[2].
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// Find this edge and then flip it
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for(TriMesh::EdgeIter it = mesh.edges_begin(); it != mesh.edges_end(); ++it) {
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if(!mesh.is_boundary(*it)) {
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// Flip edge
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mesh.flip(*it);
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}
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}
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// The edge now connects vertex vhandle[1] and vhandle[3].
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\endcode
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\section op_collapse Collapsing edges
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In this section you will learn how to collapse edges such that the
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two adjacent vertices join. %OpenMesh provides the function OpenMesh::PolyConnectivity::collapse(HalfedgeHandle _heh) to
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perform this operation. This will collapse the from-vertex (remeber that halfedges are directed)
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to the to-vertex of the halfedge as illustrated below. Note that collapsing edges
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might cause topological inconsistencies to your mesh. You should verify consistency after
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collapsing edges by calling OpenMesh::PolyConnectivity::is_collapse_ok().
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\note You have to request status attributes in order to use the collapse and delete functions!
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\image html mesh.collapse.png "Collapsing will always be performed in the direction the halfedge points to."
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A simple code example related to the illustration might look like this:
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\code
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PolyMesh mesh;
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// Request required status flags
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mesh.request_vertex_status();
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mesh.request_edge_status();
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mesh.request_face_status();
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// Add some vertices as in the illustration above
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PolyMesh::VertexHandle vhandle[7];
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vhandle[0] = mesh.add_vertex(MyMesh::Point(-1, 1, 0));
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vhandle[1] = mesh.add_vertex(MyMesh::Point(-1, 3, 0));
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vhandle[2] = mesh.add_vertex(MyMesh::Point(0, 0, 0));
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vhandle[3] = mesh.add_vertex(MyMesh::Point(0, 2, 0));
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vhandle[4] = mesh.add_vertex(MyMesh::Point(0, 4, 0));
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vhandle[5] = mesh.add_vertex(MyMesh::Point(1, 1, 0));
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vhandle[6] = mesh.add_vertex(MyMesh::Point(1, 3, 0));
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// Add three quad faces
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std::vector<PolyMesh::VertexHandle> face_vhandles;
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face_vhandles.push_back(vhandle[1]);
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face_vhandles.push_back(vhandle[0]);
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face_vhandles.push_back(vhandle[2]);
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face_vhandles.push_back(vhandle[3]);
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mesh.add_face(face_vhandles);
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face_vhandles.clear();
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face_vhandles.push_back(vhandle[1]);
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face_vhandles.push_back(vhandle[3]);
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face_vhandles.push_back(vhandle[5]);
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face_vhandles.push_back(vhandle[4]);
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mesh.add_face(face_vhandles);
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face_vhandles.clear();
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face_vhandles.push_back(vhandle[3]);
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face_vhandles.push_back(vhandle[2]);
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face_vhandles.push_back(vhandle[6]);
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face_vhandles.push_back(vhandle[5]);
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mesh.add_face(face_vhandles);
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// Now find the edge between vertex vhandle[2]
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// and vhandle[3]
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for(PolyMesh::HalfedgeIter it = mesh.halfedges_begin(); it != mesh.halfedges_end(); ++it) {
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if( mesh.to_vertex_handle(*it) == vhandle[3] &&
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mesh.from_vertex_handle(*it) == vhandle[2])
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{
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// Collapse edge
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mesh.collapse(*it);
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break;
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}
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}
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// Our mesh now looks like in the illustration above after the collapsing.
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\endcode
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*/
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