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Item A Means to Improve the GKS-3D/PHIGS Output Pipeline Implementation(Eurographics Association, 1987) Herman, Ivan; Reviczky, JanosThe output pipeline of GKS-3D/PHIGS isexamined to find some possible points where the implementation could be improved to raise efficiency while remaining strictly within the scope of the Standards. Some interesting results are presented in the paper which have led to a 25-30% improvement in speed when compared to a more conservative implementation.Item 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.Item A New Algorithm of Space Tracing Using a CSG Model(Eurographics Association, 1987) Bouatouch, Kadi; Madani, M.O.; Priol, Thierry; Arnaldi, BrunoThis paper describes a new algorithm of space tracing. Scenes are modeled by a CSG tree. Space is subdivided regularly into 3D regions called boxes. With each box is associated a subtree which is the restriction of the whole scene CSG tree to primitives belonging to this box. A 3D grid is used to access boxes.Item A New Scan Line Algorithm for the Rendering of CGS Trees(Eurographics Association, 1987) Pueyo, Xavier; Mendoza, Joan CarlesA scan line algorithm is proposed to render CSG modelled solids. Scan planes intersections are obtained by means of a proposed generalisation of Porter’s algorithm. 2-D scan plane primitives are decomposed in a way that provides a more accurate disjointness information then 3-D inclosing boxes and a simple way to class spans. Furtheremore, this scan plane organisation allows the use of most of scan line hidden surface strategies that make use of different types of coherence to speed up the visibility process.Item Generative Scene Modelling(Eurographics Association, 1987) Beyer, Thomas; Friedell, MarkWe 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.Item 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.Item A Fast Voxel Traversal Algorithm for Ray Tracing(Eurographics Association, 1987) Amanatides, John; Woo, AndrewA fast and simple voxel traversal algorithm through a 3D space partition is introduced. Going from one voxel to its neighbour requires only two floating point comparisons and one floating point addition. Also, multiple ray intersections with objects that are in more than one voxel are eliminated.Item 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.Item Bezier Patches with Local Shape Control Parameters(Eurographics Association, 1987) Schmitt, Francis J. M.; Du, Wen-HuiIn 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.Item A Fast Ray Tracing Algorithm Using Space Indexing Techniques(Eurographics Association, 1987) Qunsheng, Peng; Zhu, Yining; Liang, YoudongA fast ray tracing algorithm is presented. Spatial coherency is exploited by adopting a linear octree data structure which corresponds to an adaptive partitioning of space. A ray strides over a number of empty regions aligning on its way and intersects the desired objects directly, Efficiency of the algorithm is achieved by decreasing the number of regions that the ray must be checked with, by reducing the computations involved in skipping an empty region and by performing a binary search to find the next region. An efficient algorithm based on linear programming for mapping the whole environment into a sorted linear octree is also described. Only the terminal nodes containing boundary surfaces of objects are explicitly represented, which not only shortens the searching process but also leads to a considerable saving on storage space.