// TODO: Euler operators from http://www.cgal.org/Manual/3.2/doc_html/cgal_manual/HalfedgeDS_ref/Class_HalfedgeDS_decorator.html#Cross_link_anchor_573
/// <summary>
/// Split the face across a diagonal between two vertices a and b.
/// The returned edge has a pair of faces accessible through its
/// Faces property. edge.Faces.First will always be the new face
/// instance. edge.Faces.Second will always be the original reduced
/// face instance that was supplied as a parameter.
/// </summary>
/// <param name="face">The face to be split</param>
/// <param name="a">The start of the diagonal</param>
/// <param name="b">The end of the diagonal</param>
/// <returns></returns>
public TEdge SplitFace(FaceBase face, VertexBase a, VertexBase b)
{
// Two vertices alone are not sufficient to determine a
// unique face, so the face is also supplied. (The two
// vertices may lie on the same boundary between two faces.
Half p = a.FindHalfEdge(half => (half.Face == face));
Half q = b.FindHalfEdge(half => (half.Face == face));
Half h = p.previous;
Half g = q.previous;
return(SplitFace(h, g));
}
/// <summary>
/// Find an existing half-edge between fromVertex to toVertex
/// </summary>
/// <param name="fromVertex">The hald-edge source.</param>
/// <param name="toVertex">The half-edge target.</param>
/// <returns>An existing half-edge, or null.</returns>
private static Half FindHalf(VertexBase fromVertex, VertexBase toVertex)
{
Half result = fromVertex.FindHalfEdge(half => half.Target == toVertex);
return(result);
}
