PHIGS+ functional description revision

This is a set of proposed extensions to the proposed PHIGS graphics standard (dpANS X3.144-198x. DIS 9592) to cover the areas of lighting, shading and advanced primitives which have thus far not been addressed by that standard. This document is organized to promote its eventual integration with the existing PHIGS documentation and is therefore not tutorial in nature. It assumes that the reader is familiar with PHIGS. with rendering and with curves and surfaces. This specification has been made available to standards bodies for their consideration.