EXACT

Abstract

Computer Graphics, vol. 27, no. 4, August 1993 (SIGGRAPH ’93 Proceedings), pp. 85–92 The EXACT (EXact Area Coverage calculaTion) algorithm presented in this paper solves the Hidden Surface Elimination (HSE) problem on the subpixel level. The use of subpixel masks for anti-aliasing causes some problems with the HSE on the pixel level that are difficult to overcome. The approximations of the well known A-buffer algorithm are replaced by an exact solution that avoids erratic pixels along intersecting or touching surfaces. With EXACT the HSE problem on the subpixel level is solved with the help of p-masks. P-masks (priority masks) are subpixel masks that indicate for each subpixel which one of two given planes is closer to the viewer. An algorithm to produce the p-masks in an efficient way and its hardware implementation are presented. The p-mask generator is used in a hardware implementation of an A-buffer algorithm in the form of a rendering pipeline. Of course the algorithm can also be used in software to enhance an existing A-buffer implementation. The paper ends with the description of the list processing architecture for which the EXACT A-buffer has been built1. ∗Wilhelm–Schickard–Institut fur Informatik, Graphisch–Interaktive Systeme, Auf der Morgenstelle 10/C9, 7400 Tubingen, E-mail: andreas@gris.informatik.uni-tuebingen.de, strasser@gris.informatik.uni-tuebingen.de. 1The experiences described here were gained in a research project partly supported by the Commission of the European Communities through the ESPRIT II-Project SPIRIT-workstation, Project No. 2484. CR