Issue 4

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

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    Doctoral Theses in Computer Graphics
    (Blackwell Publishing Ltd and the Eurographics Association, 1989) Kjelldahl, Lars
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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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    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.