EG1987 Proceedings (Technical Papers)

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The Clockworks: An Object-Oriented Computer Animation System
(Eurographics Association, 1987) Breen, David E.; Getto, Phillip H.; Apodaca, Anthony A.; Schmidt, Daniel G.; Sarachan, Brion D.
The Clockworks is an object-oriented computer animation system developed at RPl's Center for Interactive Computer Graphics (CICG). The Clockworks has the ability to model and graphically simulate complex 3-D engineering processes, Its interactive capabilities also allow it be used as a design tool. Object-oriented concepts have been utilized in developing its high level architecture and its low level implementation. The Clockworks is defined as a collection of objects which communicate with the user and each other via messages. The actual implementation involved the creation of an object-oriented programming methodology using C and Unix. The complete system provides a rich research environment for exploring modelling, scripting and rendering. It also provides an interactive environment for design and a simulation environment for visual analysis of complex interacting structures.
Parallel Polygon Rendering with Precomputed Surface Patches
(Eurographics Association, 1987) Theoharis, Theoharis; Page, Ian
We describe an algorithm for rendering a restricted class of trapeziums, and hence arbitrary polygons, in parallel on an NxN SIMD array processor. The algorithm achieves good performance by precomputing “surface patches” (finite portions of half -planes), thus trading storage for increased speed. The number of surface patches that are precomputed grows only linearly with the size of the array processor but as the square of the subpixel accuracy desired. NxN texture patterns can be added at very little extra cost additional to filling a trapezium with a particular colour.
Splines for Engineers
(Eurographics Association, 1987) Ohlin, S.C.
This paper introduces the concept of interpolation consistency. It is claimed that this property is an essential one for splines that are intended for use in Computer Aided Design. Consistency is defined as the property of an interpolation algorithm that, if the given set of points is extended by any point on the interpolated curve, the algorithm applied to the extended set of points will yield exactly the same curve as before. A clear distinction is made between function interpolation, where y is a function of x, and curve interpolation, where x and y are Cartesian coordinates in the geometric plane. The class of consistent curve interpolating planear splines that corresponds to cubic function interpolation is discussed in some detail and includes the Cornu spiral, the lemniscate, and the tension-free mechanical spline. Next the class that corresponds to pentic function interpolation is considered, and an efficient algorithm is presented for the calculation of one such spline, a planar spline where the curvature is a cubic polynomial in the arclength. This algorithm produces curves where the curvature is, loosely speaking, as constant as possible. Some examples illustrating the desirable properties of this spline are given.
The Reconstruction of Neurone Morphology from Thin Optical Sections - Graphical Aspects
(Eurographics Association, 1987) Brown, A. D.; Wheal, H. V.; Stockley, E. W.
The aims of the project are two-fold: firstly, to create an accurate three-dimensional model of a neurone from the mammalian nervous system, which can be used to obtain quantitative geometric and topological data on the neurone, and secondly, to create a software simulation of an active neurone, that accurately mirrors the electrochemical responses of a real, living mammalian neurone to external excitations and to changes in its electrochemical ambient. The focus of this paper is the first of these two goals. Portions of brain tissue are prepared, containing stained neurones. Using an optical sectioning technique, these neurones can be photographed in two-dimensional slices, down to about 10um thick. These photographs are digitised, and input to a computer. The system reconstructs the three-dimensional structure of the neurone, and provides a number of ways of displaying the reconstruction.
Bezier Patches with Local Shape Control Parameters
(Eurographics Association, 1987) Schmitt, Francis J. M.; Du, Wen-Hui
In this paper, we introduce three types of shape control parmeters (tension, bias, and continuity) into the modelling of free-form surfaces composed of bicubic Bernstein-Bezier patches. This is an extension to surfaces of the three control parameters introduced in the local interpolatory spline curves by Kochanck and Bartels [12]. We first analyze the general conditions for guaranteeing the G' continuity of the surface at corners where three, four, or five patches meet. The analysis of the continuity constraints reveals the remaining degrees of freedom which can be exploited for the control of the surface shape. The shape control parameters arc then introduced. Experimental results are provided. They show the efficiency of these parameters for an easy and intuitive control of the surface shape.
An Intersection-Sensitive Hidden-Surface Algorithm
(Eurographics Association, 1987) Devai, Ferenc
Given a set of pairwise disjoint planar polygonal faces with altogether N edges in the three-dimensional space. Let k be the number of intersection points of the projections of the edges in a projection plane, 0 < k < N(N-1)/2. An algorithm for the elimination of hidden surfaces in O((N+k)log N) time and O(N+k) space is proposed. If k is O(N), which is often the case in practice, the algorithm has O(N log N) expected time, regardless of the probability distribution of the input data. The constants of proportionality are low enough to make this algorithm of practical use. The method is a three-dimensional generalization of a two-dimensional scan-line algorithm, called the NlogN algorithm. A total order hide of faces is introduced. By determining the intersections of the projected edges, regions are designated within which visibility is unvaried. Then each region is visited, maintaining the total order hide, from which visible surfaces and rendering of partially transparent objects can be inferred.
Generative Scene Modelling
(Eurographics Association, 1987) Beyer, Thomas; Friedell, Mark
We describe a new theory of scene modelling that includes generative processes as integral components of scene descriptions. A single, uniform treatment of generative processes replaces the variety of ad hoc mechanisms commonly in use. We discuss the implementation of the theory in an experimental modelling system and show that L-systems, fractals, and particle systems, as well as many specialized generative processes, become comparatively easy to define and use.
Parallel Graphical Output from Dialogue Cells
(Eurographics Association, 1987) Ten Hagen, P.J.W.; Schouten, H.J.
A system that accepts and processes graphical output from parallel processes using a single workstation, and its use in a User Interface Management System called Dialogue Cells, is described. It allows for a programmer to easily, concisely and precisely describe pictures and operations on them in a highly interactive environment. Each parallel process can do output independently, but pictures can also be moved from one process to another. Each process has its own graphical output environment. The description and implementation of the system is based on GKS.
Display of Solid Models with a Multi-Processor System
(Eurographics Association, 1987) Jansen, Frederik W.; Sutherland, Robert J.
There is a growing need for fast high-quality display of solid objects. Recently-developed custom-VLSI hardware offers high-speed display but lacks the flexibility and processing power at the pixel level to sustain the calculations and filter operations needed for realistic reflection models, texture mapping and anti-aliasing. Multi-processor systems built with general-purpose components of relatively high capacity and moderate cost provide an alternative; they also offer higher performance than single processor systems but retain their flexibility. A CSG hidden-surface algorithm based on depth-buffering and image subdivision is presented which is suitable for use with such a multi-processor system.
Viz: A Production System Based User Interface Management System
(Eurographics Association, 1987) van Harmelen, Mark; Wilson, Stephanie M.
A production system based User Interface Management System (UIMS) is discussed. The UIMS, called Viz, has been designed and implemented in a windowed workstation environment, and (a) capitalises on the graphical facilities of the workstation while (b) being designed for both textual and graphical applications. The paper considers interaction, the appearance of Viz generated interfaces, and dialogue descriptions which parameterise Viz.
Designing a System to Provide Graphical User Interfaces: The THESEUS Approach
(Eurographics Association, 1987) Huebner, W.; Lux-Mulders, G.; Muth, M.
This paper presents the design of THESEUS, a system for programming graphical user interfaces especially targetted at the area of software engineering. Starting with the special needs and requirements that arise in this area, the design alternatives for such a system - abstraction level of the programming interface, division of control and dialogue specification - are discussed. The decisions that resulted in the layer model of THESEUS are substantiated. THESEUS offers an application-oriented programming interface supporting a user interface with multiple windowing, graphics and modem interaction techniques. The dialogue control mechanisms,' event driven input management and the definition of hierarchical object-oriented output are described in detail. Experience with a first implementation is also presented.
GOCS - The GKS-oriented Communication System
(Eurographics Association, 1987) Egelhaaf, Chr.; Schuermann, G.
We present a system which offers a distributed GKS in an open network. The GKS kernel and the workstations are located on different hosts. There is no restriction to the full level 2b functionality of GKS due to the distribution. The workstation interface WSI and the communication modules, which are based on the transport protocol T.70, are discussed.
A Window Managment System on Top of GKS
(Eurographics Association, 1987) Hartelt, Helga I.M.; Magalhaes, Leo Pini; Daltrini, Beatriz Mascia
This paper presents a Window Management System, GAV, which utilizes a GKS Graphics System as a supporting tool. GAV allows the definition, by the users (designers of application programs), of several areas of visualization in the same screen. Each of these areas is a workstation according to the concept of workstation established in GKS. GAV even allows different parts of application programs to be done by different users. These users can use the full set of GKS functions in each part, without worrying about the existence of the other parts, Finally, GAV allows the grouping of workstation in sets called screen configurations. Advantages and disadvantages of the adopted solution to the problem of constructing a Window Management System are discussed.
Active-Ray Tracing for 3D Medical Imaging
(Eurographics Association, 1987) Trousset, Yves; Schmitt, Francis
Large quantities of three-dimensional (3D) information are produced by 3D medical imaging techniques such as CT and MRI, in the form of digital volumes (DV). We propose a new approach to help a human observer to visualize these volumes. This approach is based on the idea that, in order to achieve true user-interaction, segmentation and visualization should not be treated separately. This is achieved by introducing active ray tracing, a method inspired by ray tracing but working directely on unsegmented digital volumes. Segmentation takes place as the active rays penetrate through the volume.
Unifying Vector and Polygon Algorithms for Scan Conversion and Clipping
(Eurographics Association, 1987) Kilgour, AIistair
In both scan conversion and clipping, algorithm for dealing with polygons are generally presented independently of those for vectors, although many of the operations performed are similar. This paper shows how polygon algorithms for both problems can be developed from the corresponding vector algorithm. As well as yielding a unification at the conceptual level, this approach can lead to reduced code size in graphics system implementation, and produces polygon algorithms which are comparable in both robustness and efficiency with those previously presented.
Real-Time Scan-Line In-Fill
(Eurographics Association, 1987) Allerton, D. J.; Evemy, J. D.; Zaluska, E. J.
A novel algorithm is described to perform in-fill of wire-frame polygons, typically for application in visual systems for flight simulation. Post-processing is performed on an image formed in a conventional raster-scan framestore using edge-detection in scan-line order. A prototype real-time implementation of this algorithm is operational and is also presented.
A Temporal Scripting Language for Object-Oriented Animation
(Eurographics Association, 1987) Fiume, E.; Tsichritzis, D.; Dami, L.
Object orientation and concurrency are inherent to computer animation. Since the pieces of an animation can come from various media such as computer-generated imagery, video, and sound, the case for object orientation is all the stronger. However, languages for expressing the temporal co-ordination of animated objects have been slow in coming. We present such a language in this paper. Since the movements that an animated object can perform are also encapsulated as objects in our system, the scripting language can also be used to specify motion co-ordination. Such \u2018 motion objects\u201d can be applied to any animated object. The syntax, semantics, and implementation of this language will be described, and we shall show how to specify device-independent computer animation.
A VLSI System Architecture for High-Speed Radiative Transfer 3D Image Synthesis
(Eurographics Association, 1987) Bu, Jichun; Deprettere, Ed F.
In this paper we present a VLSI system architecture for high-speed synthesis of 3D images composed of diffusely reflective surfaces. The system consists of two loosely coupled sub-systems. The first sub-system computes the form-factor matrix F. The form-factor computation is based on the hemi-cube approximation technique, where the patch-to-hemi-cube projections are computed by an efficient ray-tracing algorithm. The second sub-system, a multiprocessor Gauss-Seidel iterative system solver, solves the sparse system of radiosity equations (I-AF)b=e. The described system is suitable for VLSI implementation. Pipelined CORDIC processors are used in the first sub-system, and pipelined multiplier/accumulator processors are used in the second sub-system.
A New Algorithm for Contour-plotting
(Eurographics Association, 1987) Brinkkernper, Sjaak; Hendriks, Harrie
A new algorithm for contour-plotting is introduced. The input function, tabulated or in a subroutine description, is approximated by an interpolation function. The contours of this approximating function are drawn piecewise on a subdivision of the given domain. The algorithm is based on the iterated solution of Initial Value Problems defined by applying the Implicit Function Theorem. Estimates on the dependence of the contourlines on the approximating function are presented using the method of gradient lines. Finally some examples are shown.
Interactive Generation of Fractal Objects
(Eurographics Association, 1987) Kaandorp, J. A.
In this paper a description is given of the development of data structures by which a large class of fractal objects can be represented using production rules, together with an algorithm to generate these objects. These data structures and algorithm can be used to produce many of the classical, examples of self-similar sets, mentioned for example by Mandelbrot [13]. The algorithm and data structures are part of a fractal system by which production rules can be designed; production rules can be retrieved from and stored in a fractal library.

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