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Object-oriented systems have gained a great deal of popularity recently and their application to graphics has been very successful. This book documents a number of recent advances and indicates numerous areas of current research. The purpose of the book is: - to demonstrate the extraordinary practical utility of object-oriented methods in computer graphics (including user interfaces, image synthesis, CAD), - to examine outstanding research issues in the field of object-oriented graphics, and in particular to investi- gate extensions and shortcomings of the methodology when applied to computer graphics. Papers included in the book extend existing object-oriented graphical techniques, such as Smalltalk's "model view controller" or "constraints", introduce the use of complex and persistent objects in graphics, and give approaches to direct manipulation interfaces. The reader is presented with an in-depth treatment of a number of significant existing graphics systems, both for user interfaces and for image synthesis. There are theoretical surveys and chapters pointing to new directions in the broad field of computer graphics. Computer language scientists will find a useful critique of object-oriented language constructs and suggested ways to extend object-oriented theory.



Interaction Theory and Practice


1. An Object-Oriented Framework for Direct-Manipulation User Interfaces

This chapter describes an object-oriented framework for building direct-manipulation user interfaces. Based on the concept of “mode”, the framework extends the Model-View-Con†roller (MVC) paradigm to accommodate an orthogonal design. It provides a clean structure for the user interface components and increases their reusability.
Yen-Ping Shan

2. Snap Together Mathematics

Large numbers of applications involve building complicated mathematical models out of predefined functions and repeatedly evaluating the combined function and its derivatives. For interactive applications it is important that the evaluations be efficient and that the model can be altered dynamically. Snap Together Mathematics is a facility that provides this functionality. Primitive functions are defined at compile time and can be composed dynamically to create larger models. Evaluation of both the composed function and its derivatives is accomplished by traversal of the expression graph. The sparse derivative matrix of a subset of a model’s outputs with respect to any set of its inputs can be computed efficiently. Snap Together Mathematics is implemented as a set of class definitions that provide a base for application specific objects. Among the applications we have developed are interactive systems for geometric modelling, constrained optimization, and constrained dynamics.
Michael Gleicher, Andrew Witkin

3. Building User Interfaces with the LOOKS Hyper-Object System

In this chapter, we present the LOOKS system which is designed to support the construction of user interfaces for object-oriented database applications. The looks system provides high level capabilities to display and manipulate database objects interactively and to build end-user ↔ application dialogue based on object manipulation.
Didier Plateau, Patrick Borras, Didier Lévêque, Jean-Claude Mamou, Didier Tallot

4. A Layered Object-Oriented Model for Interaction

We present a layered model of human computer interaction based on an object-oriented programming language. The model gains increasing abstraction with each layer that is added to the model. At the lowest layer parsing of physical events generated by a window system is dealt with. At the highest level we find interaction panels that no longer refer to events as such. Instead, interaction panels are solely described as aggregations of messages from High level interaction tools such as buttons, slider, menus, etc. The interaction tools are separated into three components: the interaction methods, the presentation, and the interaction style. The model can be used as a toolbox for programmers, or as a basis for automatic generation of user interfaces by interactive development tools.
Chris Laffra, Jan van den Bos

5. A 2-D Graphics System for Multi-User Interactive Graphics Based on Objects and Constraints

The MEL project is developing an object-based tool for the rapid development of graphical direct manipulation user interfaces. We emphasize interfaces to be used by multiple people from multiple workstations simultaneously. The specific requirements that multi-user interfaces place on the graphics system are discussed, as are the solutions that we have developed. In particular, the MEL graphics system is based on a hierarchical display structure of graphical objects and makes extensive use of constraints to maintain graphical consistency and link together various parts of a complete multi-user graphical program.
Ralph D. Hill

Modelling and Design


6. Persistent Graphical Objects

Persistent objects are objects whose contents may outlive the execution time of the program. This chapter describes the process of introducing persistent objects in the object-oriented programming language Procol. The strength of persistent objects in an object-oriented programming language is the integration of a database system with a programming language. Persistent objects make program development easier, because the programmer does not have to implement the explicit loading and saving of data. Besides the general functional aspects, special attention is paid to graphical applications in order to deal with their specific geometric requirements. For example, it must be possible to find, in an efficient manner, all graphical objects that fall within a given region. These issues, persistent objects and their geometric requirements, have not yet got the attention they deserve in the literature covering object-oriented graphical systems where modelling and functional aspects dominate.
Chris Laffra, Peter van Oosterom

7. Retrospective Creation of Virtual Alternative Hierarchies

In this chapter we present an object-oriented strategy to support the creation of geometric models. These models are represented as part-whole hierarchies of objects. Creation of new models is done by copying and modifying previously existing models or parts of them. Past models are stored in the system’s database and serve as prototypes for the new models.
Jan Rogier, Daan Otten

8. Coordinate Frames and Geometric Approximation in Graphics Object Oriented Programming

Coordinate transformations and coordinate systems are introduced as an object class. Finite point sets are considered as objects with internal constraints, communicating through point identifications. A geometric approximation algorithm for curve intersection based on a generic nearest-point method for curves is explored. The method is guaranteed to find an intersection point or nearest approach, depending on the starting point and specified precision. Convergence properties of the algorithm have been proved, and demonstrated in implementation. Intersection problems are thus made independent of object type, without the need for explicit algebraic solutions.
John R. Rankin, Jonathan Burns

9. A Direct Manipulation Environment for Conceptual Design of Three Dimensional Objects

The conceptual design of a three-dimensional model can be regarded as a cyclic process in which a global scheme is gradually refined into a detailed specification of components. The system presented in this chapter demonstrates how an object-oriented approach in combination with an interactive graphical environment facilitates the elaboration of a design concept during the different stages of the design process. A model is described as a part-whole hierarchy in which components are represented as interrelated graphical objects with an internal representation. Objects can be grouped bottom-up into more complex objects, or alternatively, their internal representation can be decomposed top-down into other objects. An interactive graphical interface allows the designer to view and edit both the geometric and the hierarchical organization of the model by direct manipulation.
Maarten J. G. M. van Emmerik

Graphics Systems


10. The Design of the Doré Graphics System

Doré is an application interface for three-dimensional graphics designed to provide a highly abstract core environment for applications involving both interactive display and high quality image generation. Capable of spanning multiple platforms, technologies, and interface models, its goal is to provide an extensible framework for three-dimensional graphics that can grow with rapid advances in both dynamic and photorealistic image generation.
Michael R. Kaplan

11. The New Graphics Standard — Object-Oriented!

Work towards the second generation graphics standard NewAPI has just started. This occasion is taken to compare the needs of graphics standards and the benefits of object-oriented systems. It is argued that the open demands for graphics standards can reasonably be met only by adopting an object oriented approach. Advantages of such an approach are summarized. Open issues are discussed.
Peter Wisskirchen, Klaus Kansy


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