Volume 04 (1985)

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    Calendar of Events
    (Blackwell Publishing Ltd and the Eurographics Association, 1985)
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    A Compressed Data Structure for Surface Representation
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Cottingham, Marion S.
    One of the standard methods of simplifying the task of obtaining a shaded image of a solid object is to represent it by a polyhedron. Another method is to use sculptured surface modelling which represents surfaces by collections of surface patches. Using either method the surfaces can be approximated by facets, which are simple to shade according to photometry information.To obtain a smooth image in regions of high curvature, the surface would typically be required to have hundreds or thousands of facets. Because of the large number of facets involved, it is extremely important that geometrical and topological information is stored in an efficient manner. This information must include all that is required for an unambiguous representation of the solid(s) in question.The compressed data structure (CDS) is suitable for this purpose, and is capable of defining the majority of surfaces. The structure is intended to minimise the amount of data stored, with as much information as possible being implied. The CDS can be easily generated knowing the order of the vertices defining the surface.
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    Browsing High Definition Colour Pictures
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Willis, Philip; Milford, David
    The authors describe a method of presenting colour pictures which allows users to browse by panning and zooming. The pictures are seen as though on a 512 by 512 by 12 bit framestore, but are defined to 4096 by 4096. The implementation allows the entire picture to be seen in overview, with fine details averaged, or to be zoomed in upon with finer detail progressively revealed by a sequence of twofold linear magnifications. Further zooming, beyond the resolution of the picture data, automatically produces a conventional pixel replication effect. In addition, the picture may be panned vertically or horizontally.
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    GKS Slide Sets
    (Blackwell Publishing Ltd and the Eurographics Association, 1985)
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    Dear EUROGRAPHICS Friends!
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) ten Hagen, Paul
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    Raster Graphics
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Strasser, Wolfgang
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    EDITORIAL
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Enderle, Gunter; Arnold, David
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    Interference in Computer Graphics
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Firby, P.A.; Stone, D.J.
    The interference of superposed families of curves is considered, for various types of superposition available through computer graphics. It is shown that the use of interference of this type for illustration and experimentation in hydrodynamics, optics, and in certain other situations, is rather limited. To use the technique of superposition most effectively in these areas it is found to be necessary to eliminate the interference, and to use cine techniques.
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    A General Device Driver for GKS
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Herman, I.; Reviczky, J.
    A method for generating new device drivers for use in a full GKS implementation is presented. The method is based on conditional compiling techniques making use of the Workstation Description Table, and it has been used in a full GKS to develop several device drivers, which took about 1 week for a novice.
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    The Eurographics 84 Computer Art and Animation Competition
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Comninos, Peter
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    GKS Programming in a PHIGS Environment
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Arnold, David B.; Hall, Gillian; Reynolds, Graham J.
    GKS is an international standard for the functional interface to 2D graphics, whilst PHIGS is currently an ISO work item for 2D and 3D graphics. In addition, PHIGS allows improved control over structuring graphics data in the system. With a new work item, the upwards compatability from GKS to PHIGS is being called into question. This paper is an attempt to give direction to these discussions by listing the implications of introducing a software layer between a GKS application program and a PHIGS environment on which this application is to be run. It is intended to highlight differences between the systems and to answer questions such as, "How compatible?", "Is it possible?", "How much does the software layer have to do?", etc.
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    Generating High Quality Pictures by Ray-Tracing
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Bouville, C.; Brusq, R.; Dubois, J.L.; Marchal, I.
    Ray-casting techniques provide a very general framework in which many problems can be solved in a much easier way than with conventional methods. This is particularly true for the illumination model when a high level of realism is required. Another interesting feature of ray-casting is its ability to display a wide class of algebraic surfaces with a minimum of approximation. Both aspects are developed in this paper where a full lighting model, based on a theoretical approach, is presented. Then, an algorithm for the display of surfaces of revolution is described.Computation time is the major drawback of ray-tracing. Special purpose parallel processors seem to offer a good price/performance ratio compared to the use of supercomputers.
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    Polygonal Clipping of Polylines
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Matthew, A.J.
    A Fortran routine is presented for clipping a polyline to the inside or outside of a polygon, the boundary of the polygon being treated as part of the inside. There is no limitation on the number of sides of the polygon or vectors of the polyline, and no working storage is required. The polygon may have sides that intersect and vertices or sides that coincide with each other.
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    Arbitrary Area Filling in a Fast Procedure
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Ying, Dao-Ning; Feng, Xing
    A representation for area filling is described which allows shading of an area that may have both straight lines and circular arc edges and include holes within its boundaries. For efficiency an elimination algorithm which has a waiting line list and a currently active line list is adopted. For calculating intersections, a more time saving method is used. The algorithm and some practical examples are discussed. The main features of the algorithm are execution with high speed and less storage requirement. The program is written both in BASIC and FORTRAN 77 and could be executed on a microcomputer such as APPLE II, IBM-P/C etc. The sample outputs shown in this paper are generated by the APPLE II with high efficiency.
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    Better Understanding through Formal Specification
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Duce, D. A.; Fielding, E. V. C.
    The Graphical Kernel System (GKS) is now registered as an ISO International Standard for computer graphics programming. One of the major innovations of the Standard is the bundled specification of aspects, a mechanism which gives the applications programmer the ability to tailor the appearance of a picture independently on each of the workstations on which it is displayed, using the capabilities of the workstations. GKS also incorporates the traditional method of individual specification of aspects in which each workstation does the best it can to represent global aspect values. In this paper a formal specification technique, the Vienna Development Method (VDM), is used to describe aspect specification. The GKS model of aspect specification is progressively constructed from simpler models. Properties of these simpler models are formulated and the specifications are proved to conform to these. The properties are then traced through the more complex models. The paper demonstrates the applicability of formal specification to the design of graphics software and the ability of formal techniques to catalyse the deeper understanding of designs.
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    Dear EUROGRAPHICS Friends!
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Encarnacao, Jose
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    Displaying Random Fields
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Coquillart, Sabine
    This paper presents an algorithm for random fields generation. The main idea of the paper is an improvement of the recursive technique presented by A. Fournier, D. Fussel and L. Carpenter in [4]. In order to ensure the continuity constraints on the boundaries of the cells generated at different stages of the algorithm, we show that it is possible to store the boundary values using a dynamic data structure. Random fields have been successfully used to model height fields or to display synthetic textures. In the second part of this paper we investigate the perspective mapping and clipping stages of random fields generation and display. At the end of the paper, some synthetic skies displayed using this technique are presented.
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    Institutional Membership
    (Blackwell Publishing Ltd and the Eurographics Association, 1985)
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    Book Reviews
    (Blackwell Publishing Ltd and the Eurographics Association, 1985)
    A Programmer’s Geometry by A. Bowyer and J. Woodwark.Computer Aided Design: Fundamentals and System Architecture by J. Encaracao and E.G. Schlechtendahl.
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    A General-Purpose Multi-Microprocessor Raster Graphics Display System with Anti-Aliasing
    (Blackwell Publishing Ltd and the Eurographics Association, 1985) Piller, Ernst
    The raster graphics display system described represents a general purpose mini-computer, specially for CAD applications. The system is based on a hierarchical asynchronous multiple microprocessor system. In practice this mini-computer is extendable up to 15-20 workstations. On the workstations, different graphical and non-graphical devices can be connected. The most interesting workstation is a raster graphics display device which was developed specially for the computer system described. This raster graphics display device contains a processor for the application program, two dedicated processors and two separate identical frame buffers, each of them containing one whole set of image data. Applying algorithms for anti-aliasing, virtual pixel dislocation (intensity dislocation) and multi-pixel-overlappings with hidden line (surface) elimination the image readability and quality can be increased considerably. In particular the paper deals with an anti-aliasing algorithm with a real-time hardware realization.