On Shadow Volume Silhouettes

In shadow volume rendering, the shadow volume silhouette edges are used to create primitives that model the shadow volume. A common misconception is that the vertices on such silhouettes can only be connected to two silhouette edges, i.e., have degree two. Furthermore, some believe that the degree of such a vertex can have any degree. In this short note, we present a geometric proof that shows that the degree of a silhouette vertex must be even, and not necessarily two.