Template Function lvr2::walkContour(const BaseMesh<BaseVecT>&, EdgeHandle, VisitorF, PredF)

Function Documentation

template<typename BaseVecT, typename VisitorF, typename PredF>
void lvr2::walkContour(const BaseMesh<BaseVecT> &mesh, EdgeHandle startH, VisitorF visitor, PredF exists)

Walks on a boundary contour starting at startH.

To make the method more generic, it has a exists function object which can filter out faces. Each face for which exists returns false is treated as if it wouldn’t exist in the mesh at all! If you don’t want to ignore faces, you can just not provide the exists parameter to use the other overload.

The given startH as well as all other edges on the contour mustn’t be a lonely edge (when ignoring faces according to exists).

The edges of the contour are visited in counter-clockwise order. That is, if you look at the contour as if it were a hole in the mesh. If you are thinking of the contour as an outer contour, it’s in clockwise order. This matter is pretty confusing and I don’t know how to explain it a lot better. Here another attempt:

Inner contours are visited in counter-clockwise order and outer ones in clockwise order. Inner contours are commonly referred to as “holes in the

mesh”, while the outer one is often called “mesh boundary”. However, for 3D meshes, the distinction isn’t all that clear. What matters here is the planar embedding of the mesh. There are many possible planar embeddings, including the ones that make the “mesh boundary” look like a hole and vice versa.

Anyway, we can say this for sure: given one concrete embedding for your mesh, the outer contour’s edges are returned in clockwise order and the edges of all inner contours are returned in counter-clockwise order.

Parameters:

  • visitor – A function object taking two parameters: a VertexHandle and an EdgeHandle. The vertex is the vertex of the edge that comes “before” the edge, speaking about the direction of visiting the edges.

  • exists – A function object taking one FaceHandle as parameter and returning bool. This function decides whether a face should be treated as existing or not. This is mainly used to walk on the boundary of clusters. This can be achieved by making exists return false for all faces not in the cluster.