Clipping, the process of extracting a portion of a data base, is fundamental to several aspects of computer graphics. In addition to its more typical use in selecting only the specific information required to display a particular scene or view from a larger environment, it is also useful in hidden line, hidden surface, shadow, and texture algorithms. In the context of many applications, e.g., hidden surface removal, the ability to clip concave polygons is required. Discussed below is a very powerful polygon clipping algorithm due to Kevin Weiler and Peter Atherton [6].