Table Of ContentFocus on Computer Graphics
Tutorials and Perspectives in Computer Graphics ~ o
Edited by WT. Hewitt, R. Gnatz, and W. Hansmann ~
C. Laffra E. H. Blake V. de Mey
X. Pintado
(Eds.)
Object-Oriented
Programming
for Graphics
With 102 Figures
Springer
Focus on Computer Graphics
Edited by W. T. Hewitt, R. Gnatz, and W. Hansmann
for EUROGRAPHICS -
The European Association for Computer Graphics
P. O. Box 16, CH-1288 Aire-Ia-Ville, Switzerland
Volume Editors
Chris Laffra Edwin H. Blake
Morgan Stanley & Co, Inc. University of Cape Town
1251 Avenue of the Americas Computer Science Department
New York, NY 10020, USA Rondebosch 7700, South Africa
Vicki de Mey Xavier Pintado
Apple Computer, Inc. University of Geneva
One Infinite Loop, MS: 301-41 Centre Universitaire
Cupertino, CA 95014, USA d'lnformatique,
24, rue du General-Dufour
CH-1211 Geneva 4, Suisse
Coverpicture: see contribution p. 155
ISBN-13: 978-3-642-79194-9 e-ISBN-13: 978-3-642-79192-5
DOl: 10.1007/978-3-642-79192-5
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© 1995 EUROGRAPHICS The European Association for Computer Graphics
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Preface
This book contains thoroughly revised versions of papers submitted to and pre
sented at the second and third EUROGRAPHICS workshops on Object-Oriented
Graphics.
The second workshop was held on June 4-7,1991, on the island Texel, The Nether
lands. A report by Remco Veltkamp and Edwin Blake follows. The workshop was
made possible by support of the Dutch Centre for Mathematics and Computer Sci
ence (CWI), in particular Ms. Marja Hegt, who organized all local arrangements.
Further support was given by the Dutch Software Engineering Research Center
(SERC), and by the Dutch Organization for Scientific Research (NWO).
The third workshop was held on October 28-30, 1992, in Champery, Switzerland.
A report by Nancy Craighill, Vicki de Mey, and Xavier Pintado follows. Support
was given by Centre Universitaire d'Informatique (Object Systems Group) of the
University of Geneva, Switzerland, and NeXT Inc" Switzerland.
Typesetting support for this book was given by the IBM T.J. Watson Research
Center and Morgan Stanley & Co.
December 1994 Chris Laffra
Edwin Blake
Vicki de Mey
Xavier Pintado
Contents
Report on the Second Eurographics Workshop on Object-Oriented Graphics 1
Remco Veltkamp and Edwin Blake
Report on the Third Eurographics Workshop on Object-Oriented Graphics 4
Nancy Craighill, Vicki de Mey, and Xavier Pintado
Volume I • The Second Eurographics Workshop on Object.
Oriented Graphics 9
I Modeling I 11
1 Actor-Based Simulation + Linda = Virtual Environments 13
William Leler
2 Meta-attributes for Graphics Collection Classes 23
Peter Wisskirchen
II Constraints I 31
3 A Co-operative Graphical Editor Based on Dynamically Constrained Ob-
jects 33
Zs6/ia Ruttkay
4 A Quantum Approach to Geometric Constraint Satisfaction 54
Remco C. Veltkamp
5 A Graphics Object-Oriented Constraint Solver 71
John R. Rankin
6 ALIEN: A Prototype-Based Constraint System 92
Eric Coumarie and Michel Beaudouin-Lafon
III User Interfaces I 111
7 Extending an Advanced Logic Programming Environment by an Object-
Oriented User Interface Management System 113
Heinrich Jasper
8 An Object-Oriented Architecture for Direct Manipulation Based Interac-
tive Graphic Applications: The MAGOO Architecture 127
Mario Rui Gomes, Rui Pedro Casteleiro, and Fernando Vasconcelos
VIII
9 Architecture and Use ofD2M2, the Delft Direct Manipulation Manager 136
Johan Versendaal, Willem Beekman, Marco Kruit, and Charles van der Mast
IV Rendering 153
10 An Object-Oriented Testbed for Globallllumination 155
Shenchang Eric Chen, Kenneth Turkowski, and Douglass Turner
Volume II - The Third Eurographics Workshop on Object-
Oriented Graphics 169
V Modeling II 171
11 Sharing Between Graphical Objects Using Delegation 173
D. Brookshire Conner and Andries van Dam
12 Acting on Inheritance Hierarchies 191
Adelino F. da Silva
13 The PREMO Framework: Object-Oriented Issues 204
Peter Wisskirchen
VI Constraints II 215
14 An Object-Oriented Architecture for Constraint-Based Graphical Editing 217
Richard Helm, Tien Huynh, Kim Marriott, and John Vlissides
15 Graphics Object-Oriented Platform for Euclidean Geometry Computations 239
John R. Rankin
VII User Interfaces II 251
16 The Application Exposure: Bridging the User Interface and the Application 253
Thm Z.-Y. Zhou and William J. Kubitz
VIII Experiences 269
17 An Interactive 3D Graphics Class Library in EIFFEL 271
Russell Turner, Enrico Gobbetti, Francis Balaguer, and Angelo Ma'ngili
Authors' Addresses 290
Report on The Second Eurographics
Workshop on Object-Oriented Graphics
Remco Veltkamp and Edwin Blake
Object-oriented concepts are particularly applicable to Computer Graphics in its
broadest sense - interaction, images synthesis, animation, and CAD. Research
in Object-Oriented Graphics has lead to a critique of the object-oriented theory.
The aim of the second Eurographics Workshop on Object-Oriented Graphics was
to address fundamental issues arising from the use of object-oriented techniques
in computer graphics, to provide a platform to state views on relevant issues, and
discuss possible research programmes to address remaining unresolved problems.
The workshop was held on June 4-7 on the island Texel, The Netherlands. A total
of 30 people attended the workshop, coming from The Netherlands (10 partici
pants), Germany (7), USA (4), Switzerland (3), France (2), Australia (1), Austria
(1), Portugal (1), and Turkey (1).
1 Presentations
There were 11 full papers and 13 position papers presented. The presentations were
grouped into four sessions: modelling, constraints, user interfaces, and rendering.
1.1 Modelling
This session was about issues dealing with the complexity in the design and imple
mentation of computer graphics systems. The first paper of the workshop explores
new ways to model virtual reality based on distributed control by actors, communi
cating via tuple spaces in the coordination language Linda. Other presentations in
the modelling session were about basic mechanisms for structuring graphic objects
in order to build higher structures from a kernel, flexible graphics design systems,
an object oriented implementation of compound graphical objects, the represen
tation and manipulation of structure for computer animation, and problems with
database graphics systems.
1.2 Constraints
The use of constraints in managing the complexity of designing interactive graphics
systems and the use of object-oriented methods for describing simulations and sys
tems of concrete objects have been two natural methods for building large complex
graphics systems. This widely acknowledged way of dealing with the complexities
2
of modelling and interface design has had disappointingly little practical impact.
This session explored some of the problems involved.
The topics covered were: the design of a co-operative, or intelligent, graphical ed
itor for constrained objects, the satisfaction of inter-object constraints only when
the objects' internal constraints are satisfied, the embedding of constraints in a
prototype-based system, a discussion on object-oriented vs. declarative approaches
to computer graphics, and a method for satisfaction at a geometric level, which is
particularly suited for underconstrained cases.
1.3 User Interfaces
The great benefits of class inheritance in user interface design is well recognized and
is finding increasing commercial application. Indeed, a great deal has already been
published on object-oriented design and object-oriented design of user interfaces.
The presentations in the user-interface session described the implementation of
combining a logic programming system with a user interface toolkit, an architecture
developed for direct manipulation of both application and the interface objects,
similar objectives in the context of a run time system and a tool for implementation,
a framework for object-oriented open user interfaces, and the direct interactive
generation of interactive systems.
1.4 Rendering
The last session was on rendering. A class hierarchy of geometries and associ
ated rendering algorithms naturally lend itself for an object-oriented design. The
presentations in this session discussed a toolkit for visualization offinite element
calculations using alpha-numeric messages, a test environment for global illumi
nation algorithms, ideas on object-oriented computational geometry, and volume
visualization.
2 Discussions
Not all of the above mentioned topics are found in the selected papers presented in
this book. It was felt that the more interesting part of the workshop was about the
conceptual ideas of Object-Oriented Graphics, rather than graphic implementations
using object-oriented programming techniques.
In the spirit of the constant fight between land and water in The Netherlands (we
also enjoyed an excursion to particular examples of related phenomena such as the
"wadden" sea, a "slufter", and plenty of dykes), we not only had discussions directly
related to the papers that were presented, but also an evening discussion about
Object-Oriented Graphics standards, and an ongoing discussion abqut constraints
in Object-Oriented Graphics. The discussion about standards of Object-Oriented
Graphics was meant to outline what must be provided by such a standard, and
in which way. No real consensus was achieved, and this topic was seen as a major
theme for the next workshop. In the discussions about constraints in object-oriented
3
environments, not everyone was convinced that there is a problem of possible in
fringement of information hiding. The various approaches to a solution all have
their limitations, and a more satisfying solution is yet to come.
3 Conclusion
The use of object-oriented techniques in computer graphics is a widely acknowl
edged way of dealing with the complexities in graphics systems. However, the field
of Object-Oriented Graphics is still being explored and developed, and the problems
are diverse.
In the discussions during the workshop, the following topics were found interesting
research directions: parallel techniques - can computer graphics do without?;
global and local relations between objects - when and how do they conflict with
object-oriented concepts?; extensibility of object-oriented graphics systems - how
to combine new primitives and inheritance?; operating system support - e.g. how
to support persistent objects?; object-oriented graphics standards - should it be
conservative, must (part of) the source code be provided?
Report on The Third Eurographics
Workshop on Object-Oriented Graphics
Nancy Craig hill, Vicki de Mey, and Xavier Pintado
This introduction sets the stage for the selected papers and attempts to summarize
the discussions and any conclusions made during the Third Eurographics Work
shop on Object-Oriented Graphics. The goal of the workshop was to begin outlining
a common platform, based on a set of object-oriented primitives, for the support
of graphics applications. As presentations were made, four primary topics of dis
cussion began to emerge: design of graphics objects, object model requirements,
implementation techniques and other related technology. Partly because ofthe di
verse presentations and experiences of the attendees, we made little progress on
actually identifying a common set of graphics objects. The discussions were never
theless lively and many important issues were raised.
1 Design
The design of graphics objects (the graphics kernel) can be fairly language inde
pendent and described via class hierarchy, part-whole and message flow diagrams.
1.1 Standardization
Standardization efforts are currently under way. Most felt that a common graphics
kernel could be designed but were concerned that the traditional standardization
process may not produce a good design if it does not take into account the iterative
nature of object-oriented design. Thus, any standardization effort should produce
working prototypes and establish testbeds to evaluate the reusablity, maintainabil
ity and extensibility of their design.
1.2 Modeling and Rendering Layers
It was agreed that the graphics rendering layer should be separated from the mod
eling layer-there should be two distinct graphics class categories. Thus different
renders can be easily swapped independent of the actual graphics model.
Designers must be careful about what information is passed back and forth between
modeling and rendering objects so that encapsulation is not circumvented. It is
reasonable for the modeling layer to query the rendering layer for its capabilities
in order to take appropriate actions; however, these capabilities must be defined in
some generic fashion.
