Programming Paradigms in Graphics: Proceedings of the Eurographics Workshop in Maastricht, The Netherlands, September 2–3, 1995 PDF
Preview Programming Paradigms in Graphics: Proceedings of the Eurographics Workshop in Maastricht, The Netherlands, September 2–3, 1995
Series Editors w. Hansmann W. T. Hewitt W. Purgathofer R. C. Veltkamp and E. H. Blake (eds.) Programming Paradigms in Graphics Proceedings of the Eurographics Workshop in Maastricht, The Netherlands, September 2-3, 1995 Eurographics SpringerWienNewYork Dr. Remco C. Veltkamp Department of Computer Science, University of Utrecht, The Netherlands Dr. Edwin H. Blake Department of Computer Science, University of Cape Town, Rondebosch, South Africa This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machines or similar means, and storage in data banks. © 1995 Springer-V erlag/Wien Typesetting: Camera ready by editors Graphic design: Ecke Bonk Printed on acid-free and chlorine-free bleached paper With 41 partly coloured Figures ISSN 0946-2767 ISBN-13:978-3-21 1-82788-8 e-ISBN-13:978-3-7091-9457-7 DOl: 10.1007/978-3-7091-9457-7 Preface The papers in this volume are a good sampling and overview of current solutions to the problems of creating graphically based systems. This breadth of scope comes out of the closing discussion at the Fourth Eurographics Workshop on Object-Oriented Graphics. The fifth workshop, on Programming Paradigms in Graphics, set out to provide answers and alternatives to the shortcomings of object-oriented graphics. The presentations investigated the applicability, merits and problems of various programming paradigms in computer graphics for design, modelling and implementation. This book contains a revised selection of the best papers from the Fifth Eurograph ics Workshop on Programming Paradigms in Graphics, held 2-3 September 1995 in Maastricht, The ~etherlands. All papers at the workshop were subjected to a thorough review by at least three members of the international programme committee. The se lection for this book was based on further review and the papers also incorporate the relevant aspects of the discussions at the workshop. In past Eurographics workshops on Object-Oriented Graphics the prominent trend has been a discovery of the limits of object-orientation in graphics. The limitations of object-orientation were felt to lie in such areas as the expression of relationships between objects. This is an area of particular strength for the declarative languages, such as constraint-based languages. On the other hand, a notion of state has long been a problem in declarative languages and yet it is often seen as an essential aspect of graphical modelling, particularly in simulation and animation. The lively discussions at the workshop are difficult to summarize. Reading these papers will give an idea of the issues addressed. The workshop was exciting because it brought t<?gether researchers whose common interest was graphics but not a particular programming 'ideology'. Some felt that one should not make a "theology" out of object oriented programming. The need by constraint solvers for global information and the fact that relations cannot be encapsulated in single objects could simply be addressed by relaxing the rules of information hiding and being a bit less strict about encapsulation. The purist camp felt that if violations of good practice were allowed on an ad hoc basis then the benefits conferred by object-oriented practice would simultaneously evaporate. In this connection there was some concern expressed about potential directions of the new distributed virtual reality standard for the world wide web - VRML. There might be a danger of VRML unlearning a number of the lessons learnt in developing graphics standards that have culminated in the formulation of object-oriented standards such as PREMO. The discussion sessions seemed to be good at issuing challenges. Here are a few: - Is there one paradigm for graphics or are there several sub-domains each with their own? Tie up subdomains with their corresponding paradigms. - Conceptually speaking, what are the limitations of object-oriented and functional programming paradigms? Is it as crude as that one cannot deal with relationships VI while the other leads to rather contorted ways of regarding persistent actors changing over time? - What, if anything, is special about the requirements that graphics (in the broad sense) imposes on programming methodologies? - Specifically, please present, at the next workshop, a useful functional animation system. a well designed VRML. with object-orientation as a base, an integration of other paradigms that works "well". Well means that the integration confers the sum ofthe benefits of the individual paradigms and not the lowest common factor. Start by integrating a functional paradigm. a working prototype for every claim; one that effectively demonstrates the solu tion. This is a call for constructed proofs. One of the conclusions of the workshop was that the object-oriented methodology is still the most effective approach that is widely used to construct real computer graphics applications. Leaving its role as an implementation tool aside, practitioners have realized the shortcomings of the object-oriented methodology as a conceptual problem solving paradigm for the design and development of large computer graphics applications. The availability of powerful parallel systems and high-speed networks, the phenomenal popularity of World Wide Web, the advent of global computing, and the promise of information super-highways all allow graphics applications to extend the limits of how computers can impact our professional, personal, and social lives. In this context, concurrency an~ distribution have been proposed as one of the themes of the next workshop in this series. Deferred processing (related to laziness) is important in large animated systems and it is still an open question. The need for extensibility of graphical systems, particularly by third parties without access to source code, should also be addressed more adequately than at present. The papers are grouped into four parts: Object-Oriented, Constraints, Functional, and Multi-Paradigm. This essentially takes the reader on a tour of the issues we have addressed. Firstly there are the impressive benefits and power of object-oriented ap proaches, both as conceptually tools for design and as programming frameworks. In constraints, though, the limitations are exposed, and addressed. Functional program ming provides a clear alternative approach with some impressive recent breakthroughs conceptually (e.g., the use of monads to express state) and in practice. Finally we present some approaches to resolving (or at least enumerating) the mUltiplicity of approaches encountered. The ERCIM Graphics Network supported the workshop. The workshop was orga nized by CWI, Amsterdam. We thank Ms. Marja Hegt for assistance and organizing local arrangements. October 1995 Edwin Blake Remco Veltkamp Contents Part I: Object-Oriented Issues on Hierarchical Graphical Scenes ...................................... 3 E. Beier Utilizing Renderer Efficiencies in an Object-Oriented Graphics System. . . . . . . .. . 13 P.K. Egbert Object-Oriented Design for Image Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 23 P. Slusallek and H-P' Seidel Part II: Constraints Supporting Interactive Animation Using Multi-way Constraints ................. 37 l.-F. Balaguerand E. Gobbetti Information Hiding and the Complexity of Constraint Satisfaction .............. 49 R. C. Veltkamp and R.HM. C. Kelleners Part ill: Functional Constructive Solid Geometry using Algorithmic Skeletons ..................... 69 1.R. Davy, H Deldari, and P.H Dew Composing Haggis ........................................................ 85 S. Finne and S. Peyton lanes Functional Specification of JPEG Decompression, and an Implementation for Free ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 102 I. Fokker Part IV: Multi-Paradigm The "No-Paradigm" Programming Paradigm for Information Visualization ...... 121 E.H. Blake and H.A. Goosen VIII Reactivity, Concurrency, Data-flow and Hierarchical Preemption for Behavioural Animation ............................................................... 137 S. Donikian and E. Rutten A Dual-Paradigm Approach to Database Generation for Visual Simulation '. ..... 154 M.D.l. McNeill, S.J. Lambourn, P.F. Lister, and R.L. Grimsdale Appendix: Colour Illustrations ............................................. 167 Part I: Object-Oriented Issues on Hierarchical Graphical Scenes Ekkehard Beier Technical University of I1menau, Department of Computer Graphics E-mail: [email protected] Abstract A hierarchical structuring of graphical scenes corresponds to many real world metaphors and implies an ease of use. But, due to the limited resources of graphical systems, graphical scenes are often created as directed acyclic graphs and, therefore, are loosing the advantages of hierarchies. This paper explores the requirements of various rendering methods with regard to the organization of the graphical scene, and sets up rendering-independent mod elling requirements for a generic graphics kernel. Finally, it describes a solution for a specific graphics kernel that is strongly based on hierarchical structures but avoids redundancies in a high degree. 1 Introduction Most real world metaphors are based on hierarchies. Therefore, the usage of hierarchies in computer graphics is quite natural and implies an ease of use. However, due to the limited resources of graphical systems, scenes are often created as directed acyclic graphs (DAG) and, therefore, are loosing the advantages of hierarchies. Thus, two major paradigms exist for the organization of graphical output, the hierarchy and the DAG. The usage of hierarchies has several advantages, e.g., clear object locations and parent relations, natural manipulations of the scene and, statically bound objects may be realized. This allows, for instance, an efficient implementation of object-oriented modelling paradigms by using retraversing as described in [2]. Hierarchies do not imply the problems which may be encountered when using the DAG approach, that is, the ambiguity of the parent of a primitive, the restructuring of the DAG into a tree in order to do some specific tasks (e.g., pick correlation or individualization of multiply referenced data). On the other hand, a hierarchical approach causes a certain amount of redundancy for most application areas. The DAG-oriented structure is characterized by multiple usage of data, i.e., geometry and attributes. This saves memory needs and start-up time in a degree dependent on the existence of similar data structures. Application fields with a high degree of redundancy are, for instance, circuit design, furniture visualization or virtual reality. Drawbacks of this approach are the needs for traversing processes due to the dynamically bound objects with a certain amount of computing efforts and the limited navigation possibilities within theDAG. Both approaches correspond to various kinds of rendering in a different degree. This will be shortly explained in the following section. Based on these examinations rendering-independent modelling requirements will be set up that may be inherent to
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