Issue 4

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https://diglib.eg.org/handle/10.2312/34

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    2-D Macroscopic Texture Synthesis
    (Blackwell Publishing Ltd and the Eurographics Association, 1989) Bennis, Chakib; Gagalowicz, Andre
    We present a new macroscopic texture synthesis method based upon a hierarchical macroscopic texture model. Our model allows the composition of various patterns which can be themselves distorted spatially. Such a method is able to simulate a vast class of realistic macro-textures.
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    Anti-aliased Ray Tracing with Covers
    (Blackwell Publishing Ltd and the Eurographics Association, 1989) Thomas, D.; Netravali, Arun N.; Fox, D.S.
    A fast and effective object space method for antialiasing ray-traced pictures is introduced. Traditionally, anti-aliasing has been done using super-sampling. However, this is costly since it requires casting large numbers of rays to obtain sample densities above the displayed pixel density. It is also wasteful since much of the information in these samples is discarded when they are filtered to yield the anti-aliased pixels. We avoid these problems by performing the filtering in the object space using the geometry of ray-surface intersections rather than by casting extra rays. In addition, we only perform filtering at a pixel if edges are nearby. We detect these edges by observing the order in which the pixel s rays pass through cover surfaces constructed just inside and outside the surface of each object. Shadows, reflections and refractions can be anti-aliased using this method and a variety of object types can be handled including ellipsoids, polyhedra, and objects formed using set operations.Our anti-aliasing gives a high image quality that can only be approached by using super-sampling densities at least four times the display pixel density. Moreover, since the overhead of our method is small, it would take three to four times as long to render an anti-aliased image using super-sampling than it would with our method. Furthermore, covers allow sampling densities less than the displayed pixel density. When this is done, anti-aliased images can be rendered twice as fast as with no anti-aliasing and six to eight times as fast as when super-sampling is used for anti-aliasing.
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    Book Reviews
    (Blackwell Publishing Ltd and the Eurographics Association, 1989)
    Book reviewed in this article:Title: Image Synthesis - Elementary Algorithms Author: Gerard Hegron Translation (by D. Beeson) of: Synthese d Image: Algorithmes ElementairesCurves and Surfaces in Computer Aided Geometric Design Author: F. Yamaguchi
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    Doctoral Theses in Computer Graphics
    (Blackwell Publishing Ltd and the Eurographics Association, 1989) Kjelldahl, Lars
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    EDITORIAL
    (Blackwell Publishing Ltd and the Eurographics Association, 1989) Arnold, David; de Ruiter, Behr
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    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.
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    A Method for the Representation, Evaluation and Display of CSG Models in PHIGS and PHIGS+
    (Blackwell Publishing Ltd and the Eurographics Association, 1989) Patel, Manjula
    The Programmer s Hierarchical Interactive Graphics System (PHIGS) is about to become a standard graphics system? which caters for the definition, display and modification of two and three-dimensional graphical data.PHIGS, however, is mainly a wireframe system, and the PHIGS+, extensions to it have been put forward to allow the incorporation of shaded 3D graphics into PHIGS.,One area that is important to a large constituency and which has so far not been considered in PHIGS, and PHIGS+, is that of solid modelling. This paper addresses one aspect of solid modelling by describing a simple method for the representation, evaluation and display of Constructive Solid Geometry (CSG) models in PHIGS, and PHIGS+..
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    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.
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    On The Projective Invariant Representation of Conies in Computer Graphics
    (Blackwell Publishing Ltd and the Eurographics Association, 1989) Herman, Ivan
    A general formulation for conies and conic arcs for the purpose of computer graphics is given, based on principles and theorems of projective geometry. This approach allows the approximation of these curves by line segments to be postponed in the graphics output pipeline- it results in a more compact storage, faster approximation algorithms and smoother outlook of the curves.