Volume 06 (1987)
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Item An Implementer s View of CGM in GKS Environment(Blackwell Publishing Ltd and the Eurographics Association, 1987) Moltedo, L.; Noferini, A.Item Executive Committee Nominations -1987(Blackwell Publishing Ltd and the Eurographics Association, 1987)Item A Simple and Efficient Haloed Line Algorithm for Hidden Line Elimination(Blackwell Publishing Ltd and the Eurographics Association, 1987) Franklin, W.R; Akman, V.An efficient algorithm, HALO, is given to compute haloed line drawings of wire frame objects. Haloed line drawings are described by Appel et al.1HALO has two parts: CUT and DRAW. CUT uses an adaptive grid to find all edge intersections. It overlays a square grid, whose fineness is a function of the number and length of the edges, on the Scene. It determines the cells that each edge passes through, sorts these by cell to obtain the edges in each cell, and then, in each cell, tests each pair of edges in that cell for intersection. For broad classes of input this takes time linear in the number of edges plus the number of intersections. CUT writes a file containing all the locations where each edge is crossed in front by another. Given a halo width, DRAW reads this file edge by edge. For each edge, it subtracts and adds the halo width to each intersection to get the locations where the edge becomes invisible and visible. It sorts these along the edge, and then traverses the edge, plotting those portions where the number of"Visible" transitions is equal to the number of"invisible" transitions. DRAW takes time hear in the number of edge segments. Dividing HALO into two parts means that redrawing a plot with a different halo width is fast, since only DRAW need to be rerun.CR Categories and Subject Descriptions: I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling - geometric algorithm, languages, and systems- F.2.2 [Analysis of Algorithms and Problem Complexity]: Nonnumerid Algorithms and Problems -geometrical problem and computationsGeneral Terms: Algorithms, design.Item Calendar of Events(Blackwell Publishing Ltd and the Eurographics Association, 1987)Item Parallel Polygon Rendering with Precomputed Surface Patches(Eurographics Association, 1987) Theoharis, Theoharis; Page, IanWe 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.Item A Scanline Method for Solid Model Display(Blackwell Publishing Ltd and the Eurographics Association, 1987) Patel, Manjula; Hubbold, Roger J.The modelling of solid objects is becoming increasingly important in the application of computer graphics to a wide variety of problems, such as CAD/CAM, simulation, and molecular modelling. A variety of methods for rendering solid objects exists, including 2-Buffer, Scanline and Ray Tracing. This paper is concerned with a scanline method for the production of still images of complex objects. The implementation of a scanline algorithm is discussed, in conjunction with a consideration of its performance in relation to the z-buffer method.Many scanline methods cater only for a restricted class of primitives, such as polygons or spheres, whereas this implementation is a general purpose scanline algorithm capable of being extended to handle a variety of primitives. The primitives currently available are polygons, spheres, spheres swept along straight-line trajectories, and cylinders. Polygonal models of cubes, cones and cylinders are also available.The approach is capable of dealing with"positive" and"negative" volumes, allowing objects with holes to be modelled and displayed. It has further been extended to cater for the inclusion of transparent objects into a scene, and consequently allows the modelling of coloured"glass" objects.Item Scan Converting Extruded Lines at Ultra High Definition(Blackwell Publishing Ltd and the Eurographics Association, 1987) Willis, Philip; Watters, GeoffWe consider the problem of generating freehand raster graphics pictures at ultra high definition (typically one gigapixel per picture) by scan converting extruded lines. We describe a fast scan conversion algorithm which is linear in final resolution and which incorporates a number of features to ensure high efficiency. Sample pictures and corresponding performance figures are included.Item 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.Item EUROGRAPHICS Membership Application Forms(Blackwell Publishing Ltd and the Eurographics Association, 1987)Item Offers to EUROGRAPHICS Members(Blackwell Publishing Ltd and the Eurographics Association, 1987)Item COLOUR SECTION(Eurographics Association, 1987) -Item 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.Item Unifying Vector and Polygon Algorithms for Scan Conversion and Clipping(Eurographics Association, 1987) Kilgour, AIistairIn 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.Item EUROGRAPHICS General Assembly(Blackwell Publishing Ltd and the Eurographics Association, 1987)Item Active-Ray Tracing for 3D Medical Imaging(Eurographics Association, 1987) Trousset, Yves; Schmitt, FrancisLarge 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.Item Graphics, Bifurcation, Order and Chaos(Blackwell Publishing Ltd and the Eurographics Association, 1987) Pickover, C.A.Chaos theory involves the study of how complicated behaviour can arise in systems which are based on simple rules, and how minute changes in the input of a system can lead to large differences in the output. In this paper, bifurcation maps of the education Xt+1=??Xt [1+Xt] -?, where ?= 1 or ?=e-Xi, are presented, and they reveal a visually striking and intricate class of patterns ranging from stable points, to a bifurcating hierarchy of stable cycles, to apparently random fluctuations. The computer-based system presented is special in its primary focus on the fast characterization of simple"chacs equation" data using an interactive graphics system with a variety of controlling parameters.Item Evaluation of Standard Graphics Packages(Blackwell Publishing Ltd and the Eurographics Association, 1987) Klok, FopkeIn order to compare the quality of different implementations of GKS, the ISO0 standard for computer graphics, an evaluation method for GKS implementations is presented. It is based upon several groups of criteria. One group of criteria is concerned with performance, by which we understand here the memory requirements and time requirements for programs using GKS functions. A program that measures the performance of GKS packages is presented. Results of this evaluation method with several commercially available GKS implementations are described in summary. A checklist for evaluation of standard graphics packages is added as an appendix.Item Offers to EUROGRAPMCS Members(Blackwell Publishing Ltd and the Eurographics Association, 1987)Item 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.Item GKS Review Workshop(Blackwell Publishing Ltd and the Eurographics Association, 1987)