A geometry and lighting graphics accelerator with an improved clipping process. Clipping is performed prior to any calculation or evaluation of primitives for lighting, texture, fog, or color. Barycentric coordinates are used to define all vertices: original, intermediate, and final intersection points. Use of barycentric coordinates results in less storage space. A circular buffer is used during the clipping process to store input and output polygons. Use of the circular buffer also results is reduced storage requirements.