Volume 08 (1989)

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Interesting New Tutorial Topics at Eurgraphics 89
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Purgathofer, W.; Schonhut, J.
Visualizing Curvature Discontinuities of Free-Form Surfaces
(Eurographics Association, 1989) Pottmann, Helmut
A new method for the visualization of curvature discontinuities of free-form surfaces is presented. It is based upon an improvement and refinement of the well-known technique of displaying isophotes.
Report of the Third International Conference on Computer Graphics June 22-24, 1988, Dubrovnik, Yugoslavia
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Suzjevic, V.
Motion Control in Animation, Simulation and Visualization*
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Hegror, Gerard; Palamidese, Patrizia; Thalmann, Daniel
This paper discusses the role and the evolution of animation, simulation and scientific visualization and their relationships. Two trends are described: (1) the physical laws are well-known and their use improves the animation- (2) the physical laws are not really well-known and the animation techniques contribute to understanding them. We distinguish descriptive models used to reproduce an effect without knowledge about its cause and generative models describing the cause which produces the effects. Cooperation between descriptive and generative models is also discussed as well as man-machine interface constraints. Finally, the evolution of animation towards automatic motion control, goal-oriented motion, task modeling and behavioural animation is emphasized.
LEONARDO - New Member Benefit for Members of Eurographics
(Blackwell Publishing Ltd and the Eurographics Association, 1989)
EUROGRAPHICS UK Chapter Conference CGM Demonstration
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Duce, D.A.
Graph Grammars, A New Paradigm for Implementing Visual Languages
(Eurographics Association, 1989) Goettler, Herbert
This paper is a report on an ongoing work which started in 1981 and is aiming at a general method which would help to considerably reduce the time necessary to develop a syntax-directed editor for any given diagram technique. The main idea behind the approach is to represent diagrams by (formal) graphs whose nodes are enriched with attributes. Then, any manipulation of a diagram (typically the insertion of an arrow, a box, text, coloring, etc.) can be expressed in terms of the manipulation of its underlying attributed representation graph. The formal description of the manipulation is done by programmed attributed graph grammars.
Hierarchical Texture Synthesis on 3-D Surfaces
(Eurographics Association, 1989) Bennis, Chakib; Gagalowicz, Andre
This paper presents a new method for synthesizing hierarchical textures on 3-D surfaces. This method utilizes both a mapping technique for rendering the macroscopic structure on the surface and a generalization of the direct 3-D microscopic synthesis algorithms (presented in earlier publications) for generating a homogeneous texture inside each pattern. To produce the macroscopic structure on the 3-D shape a new mapping technique is proposed. With this technique patterns distortion is minimized locally. Finally a solution to the aliasing problem adapted to our mapping is given.
A VLSI Chip for Ray Tracing Bicubic Patches
(Eurographics Association, 1989) Bouatouch, Kadi; Saouter, Yannick; Candela, Jean Charles
This paper deals with the integration of a VLSI chip dedicated to ray tracing bicubic patches. A recursive subdivision algorithm is embedded in this chip. The recursion stops when the termination conditions are met. A software implementation allowed for the determination of key parameters which influenced the choice of the proposed chip' architecture. Only some modules of the chip are, at the present time, simulated and laid out, the rest is being implemented. A detailed description of the chip' modules is given.
Variations on a Dither Algorithm
(Eurographics Association, 1989) Pins, Markus; Hild, Hermann
Mapping continuous-tone pictures into digital halftone pictures, i.e. 0/1-pictures, for printing purposes is a well explored technique. In this paper, one of these algorithms, the two-dimensional error-diffusion algorithm is extended to color pictures and animated pictures. The color picture algorithm is superior to existing algorithms by considering extreme color values as well as adjacent color values. The animation algorithm eliminates the noise created by the correct but varying pixel patterns generated by applying a single picture dithering algorithm on every frame. The power of the algorithms is demonstrated by experiments carried out on synthetic images generated by ray tracing.
EDITORIAL
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Arnold, David; de Ruiter, Behr
A Survey of GKS and PfflGS Implementations October 1988
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Wyrwas, K.M.; Hewitt, W.T.
Faster Phong Shading via Angular Interpolation
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Kuijk, AAM.; Blake, E.H.
One of the most successful algorithms that brought realism to the world of 3D image generation is Phong shading. It is an algorithm for smooth shading meshes of planar polygons used to represent curved surfaces. The level of realism and depth perception that can be obtained by Phong shading is attractive for 3D CAD applications and related areas. However, per pixel computation costs which were too high and/or artifacts, introduced by some of the more efficient evaluation methods and apparent only when displaying moving objects, are major factors mat blocked the common usage of Phong shading in highly interactive applications.In this paper we present angular interpolation for Phong shading planar polygons. Angular interpolation was a method especially designed to meet requirements as imposed by special purpose hardware we developed1, but turned out to be generally applicable. The angular interpolation method appears to be very efficient and reduces artifacts when displaying moving objects. Ideally a shading algorithm imposes no need for subdivision of patches as presented by the solid modelling system. Shading calculation via angular interpolation yields such an ideal algorithm. We will describe two alternative evaluation methods that trade off evaluation cost against level of accuracy. They both can handle light source and view point at arbitrary distances, but differ in level of accuracy. As a consequence these alternative evaluation methods do impose restrictions on the topology of patches and light sources. However, generally, the limitations imposed by these alternative shading methods are much more liberal than the limitations on patch size imposed by the geometry.The most economic evaluation method we present can incrementally compute the colour intensity along a scanline by two additions per pixel. The methods presented are generally applicable and can easily be implemented in hardware.
Algorithm for Clipping Arbitrary Polygons
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Andreev, Rumen D.
Doctoral Theses in Computer Graphics
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Kjelldahl, Lars
Blending Rational B-Spline Surfaces
(Eurographics Association, 1989) Bardis, L.; Patrikalakis, N.M.
A method for blendin non uniform rational B-spline surface patches, either open or periodic, is developed. he blending surface is expressed in terms of an integral, bicubic B-spline patch. The blend ensures position and normal vector continuity along linkage curves to within a specified accuracy. The linkage curves are either user-defined or are obtained by offsetting the intersection of the two patches using geodesics on each patch. An example illustrates the applicability of our method.
Highlight Shading: Lighting and Shading in a PHIGS+/PEX-Environment
(Eurographics Association, 1989) Poepsel, J.; Hornung, C.
Todays graphics standard for the rendering of scenes with illumination and reflection is defined by PHIGS+ . PEX is a proposal to integrate that functionality into the window environment of X. This paper first describes the lighting and shading models of PHIGS+/- PEX . Then a comparison of the different shading methods follows. At last, a new shading method, the Highlight Shading, is developed. The Highlight Shading combines both speed and image quality and therefore is an attractive alternative to existing shading algorithms.
A Model for Description and Synthesis of Heterogeneous Textures
(Eurographics Association, 1989) Englert, Gabriele; Sakas, Georgios
Existing texture models either describe textures as a non-hierarchical surface property (by means of Markov chains, time series and other stochastic methods) or distinguish only between micro and macro textures. Besides this, textures are used in general only for mapping colour-information (usually derived from digitized photographs) on the object surface or for varying the normal vector of a given surface (bumps mapping). In addition, the different models are strongly combined with special generation algorithms and the produced textures are exclusively raster images. As a consequence, the above models are not able to describe more than a few types of textures. In this paper a definition of the term texture is first presented and a hierarchical texture model in accordance with the above definition is then proposed. We provide complete textures, consisting of several slices, to be mapped on geometrical objects. Each slice represents an optical surface property. These properties are. approximated by the different parameters of an illumination model. The slices themselves are hierarchical compositions of several levels. Each "intermediate texture" is derived by operations (transformations and combinations) performed on the textures of the next lower level. A texture is not limited in space and is described by means of a complete texture function which affects all texture slices. Such functions can be either usual algebraical functions, or they can determine the placement of elements on the texture plane.
8th EUROGRAPHICS UK Conference
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Willis, P.J.
Using a Transputer Ring to Transform Raster Images
(Blackwell Publishing Ltd and the Eurographics Association, 1989) Rush, Stephen; Milne, Wendy

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