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In Issue 8(4) of Computer Graphics Forum, the last issue of the 80's, contains five refereed papers, along with the usual clutch of reports of events, book reviews and a listing with descriptions of recent PhD theses in computer graphics and related areas.

The 6rst paper in the issue, by Bennis and Gagalowin, presents a method of handling patterns as a structured description giving the opportunity to manipulate the pattern definition at both a macros- copic and microscopic level. This gives them the ability to produce in each pattern a separation between the material and the pattern in which the material is included and then to provide distorsions to each. The advantage claimed for the method is that the computing resources used are comparable to previous unstructured methods. The reader is also referred to the paper by the authors in the EURO- GRAPHICS '89 Proceedings, which describes other aspects of their work.

Ivan Herman's paper presents a general formulation for conics and conic arcs based on principles and theorems of projective geometry and suitable for computer graphics. Use of this formulation in the graphics pipeline would allow the conics to be handled as conics right up to the rendering stage (i.e. without using polyline approximations to compensate for inadequate projection or segment handling software). This gives economies in data volumes in the pipeline and in storage and hence to perfor- mance improvements. In addition since the actual approximation used can now be tailored to the final view used in the rendering, smoother visualisations are possible without overkill in u ~ ~ ~ s s a r i l y fine approximations in regions of small detail, for example. Herman concludes that projective invariant representations should be sought for any primitive used in the pipeline, and urges the reader to revisit classical geometrical techniques to seek pointers to better methods in computer graphics.

Kuijk and Blake present the latest of a recent spate of papers in the area of improvements to Phong shading algorithms. In their approach they use angular interpolation for Phong shading of planar polygons which leads to economies in the normalisation stage of processing normal Phong shad- ing. They also propose some approximation methods which provide additional speedups. This paper is closely related to two papers given at EUROGRAPHICS '89, which were awarded the fmt and third prizes in the Best Paper Competition. In particular the paper by Ute Claussen, which is refered to by Kuijk and Blake, is recommended as additional reading for those investigating the area. The paper by Popsel and Hornung is also related.

Thomas, Netravali and Fox present a method for producing ray-traced and anti-aliased images using object space anti-aliasing. There method avoids the computational expense of supersampling and by using covers around surfaces of objects of interest in antialiasing a scene, they reduce the number of intersection tests used in the anti-aliasing. The results they report show a quality of rendering equivalent to use of super-sampling at at least four times the pixel density.

The final paper in this issue, by Manjula Patel, proposes a method for incorporating CSG models into a PHIGS or PHIGS PLUS system. She demonstrates that most of the essential components are already there, but that there would be a need to cater for regulised Boolean operators within the PHIGS system and to incorporate checks that primitives used did define enclosed, bounded volumes. The only alternative would be to build the modelling system on top of the PHIGS system reducing its usefulness in the support of CSG applications. This paper is related in some ways to that by Ivan Her- man described above, in that the motivation is to try and bring the data as far down the graphics pipe- line as possible in a form which remains close to its original definition and therefore allows usefullocal manipulation, close to the point of rendering. It would therefore be a shame if the conclusion of the work was a need to build on top of the standard system.

290 Editorial

Tlus then is Computer Graphics Forum 8(4), which we take pleasure in recommending to our readers. The editors would Like to take this opportunity of wishing all readers seasonal greetings and all good fortune as we move into the 1990’s.

David Arnold Behr de Ruiter