Issue 4

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https://diglib.eg.org/handle/10.2312/40

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    A Direct Manipulation Technique for Specifying 3D Object Transformations with a 2D Input Device
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Van Emmerik, Maarten J.G.M.
    A mechanism is presented for direct manipulation of 3D objects with a conventional 2D input device, such as a mouse. The user can define and modify a model by graphical interaction on a 3D perspective or parallel projection. A gestural interface technique enables the specification of 3D transformations (translation, rotation and scaling) by 2D pick and drag operations. Interaction is not restricted to single objects but can be applied to compound objects as well. The method described in this paper is an easy-to-understand 3D input technique which does not require any special hardware and is compatible with the designer s mental model of object manipulation.
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    The Implementation of a 2D Convex Hull Algorithm Using Perturbation
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Day, A.M.
    This paper discusses the problem of geometric degeneracies and outlines possible solutions when converting geometric algorithms into practice. It concentrates on the application of one of the suggested solutions, a perturbation technique, to a 2D convex hull program. An outline of the relevant theory and its conversion into practice is given. Experimental results are presented and discussed.
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    Book Reviews
    (Blackwell Publishing Ltd and the Eurographics Association, 1990)
    Book reviewed in this article:Advances in Computer Graphics V Purgathofer, W., and Schiinhut, J. (editors)An Introduction to Ray Tracing, Glassner, AS. (editor)
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    GosiP: A GKS3D Shell for PHIGS
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) French, Michael
    Gosip is an implementation of a GKS-3D level 2c interface to PHIGS. It allows GKS applications to run on PHIGS platforms, offering performance and portability across a wide range of high-performance 3D workstations. Compatibility of the standards is reviewed. A selection of design solutions is given for the problems of error processing, non-retained primitives and attribute management. The concepts of Workstation Display Session and atmbute state are introduced. Some comments are made on implementation dependencies, performance and portability.
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    Durer, Gaskets and Barnsley s Chaos Game
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Jones, Huw
    Michael Barnsley has generated the Sierpinski triangle or gasket using his"Chaos Game", a technique for generating random points within a fractal object. Extensions of the method are discussed to generate fractal"gaskets" based on other regular polygons. One such figure resembles a tiling pattern based on pentagons known to Albrecht Durer almost 500 years ago.
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    Simulating Natural Light
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Wu, Jintong
    Simulating natural light is an interesting subject in computer graphics. Using the principles of meteorology, we build a sphere cap light source model. Unlike existing illumination or light source models, we consider the effects of both the ratio of direct light to diffuse light and the position of the sun under different weather conditions. We use an area light source to generate shadows and a point light source to generate the other effects. The ratio of the two types of light is adjusted by a brightness factor b while the position of the sun is determined by giving the light direction. In addition. a modifiable sphere cap is used to obtain modified penumbra which vary with illumination.
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    3D Display: Synthetic Image Generation and Visual Effect Simulation
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Theoharis, T. A.; Travis, A. R. L.; Wiseman, N. E.
    Two viewing models are presented for a promising type of three dimensional display: they are based on parallel oblique and perspective oblique projections respectively. A detailed simulation compares the quality of the images that will be produced by each projection type and points out potential problems. The time necessary to alter the image of the three dimensional display will be comparable to that of conventional displays by the use of a simple parallel processing scheme.
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    EDITORIAL
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Arnold, David
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    An Efficient Circle-Drawing Algorithm
    (Blackwell Publishing Ltd and the Eurographics Association, 1990) Kuzmin, Yevgeni P.
    An efficient incremental circledrawing algorithm which uses paired update of the decision variable is proposed. The output of the algorithm is identical to the output of Bresenham s algorithm but the total number of arithmetical operations is less. Efficiency of the algorithm is independent of the output devices. Its other advantages are discussed.