C# Class LibTessDotNet.Tess

DiscardExterior zaps (ie. sets to null) all faces which are not marked "inside" the polygon. Since further mesh operations on NULL faces are not allowed, the main purpose is to clean up the mesh so that exterior loops are not represented in the data structure.

SetWindingNumber( value, keepOnlyBoundary ) resets the winding numbers on all edges so that regions marked "inside" the polygon have a winding number of "value", and regions outside have a winding number of 0. If keepOnlyBoundary is TRUE, it also deletes all edges which do not separate an interior region from an exterior one.

TessellateInterior( mesh ) tessellates each region of the mesh which is marked "inside" the polygon. Each such region must be monotone.

TessellateMonoRegion( face ) tessellates a monotone region (what else would it do??) The region must consist of a single loop of half-edges (see mesh.h) oriented CCW. "Monotone" in this case means that any vertical line intersects the interior of the region in a single interval. Tessellation consists of adding interior edges (actually pairs of half-edges), to split the region into non-overlapping triangles. The basic idea is explained in Preparata and Shamos (which I don't have handy right now), although their implementation is more complicated than this one. The are two edge chains, an upper chain and a lower chain. We process all vertices from both chains in order, from right to left. The algorithm ensures that the following invariant holds after each vertex is processed: the untessellated region consists of two chains, where one chain (say the upper) is a single edge, and the other chain is concave. The left vertex of the single edge is always to the left of all vertices in the concave chain. Each step consists of adding the rightmost unprocessed vertex to one of the two chains, and forming a fan of triangles from the rightmost of two chain endpoints. Determining whether we can add each triangle to the fan is a simple orientation test. By making the fan as large as possible, we restore the invariant (check it yourself).