At present, object-oriented programming is emerging from the research labora­ tories and invading into the field of industrial applications. More and more products have been implemented with the aid of object-oriented programming techniques and tools, usually as extensions of traditional languages in hybrid development systems. Some of the better known examples are OSF-Motif, News, Objective-C on the NeXT computer, the C extension C++, and CLOS an object­ oriented extension of LISP. All of these developments incorporate interactive graphics. Effective object-oriented systems in combination with a graphics kernel­ does it mean that the field of computer graphics has now become merely an aspect of the object-oriented world? We do not think so. In spite of interesting individual developments, there are still no sound object-oriented graphics sys­ tems available. If it is desired to develop a complex graphics application embed­ ded in a window-oriented system then it is still necessary to work with elemen­ tary tools. What is to be displayed and interactively modified inside a window must be specified with a set of graphics primitives at a low level, or has to be written with a standardized graphics kernel system such as GKS or PHIGS, i. e. , by kernels specified and implemented in a non-object-oriented style. With the terms GKS and PHIGS we enter the world of international graphics standards. GKS and PHIGS constitute systems, not mere collections of graphics primitives.

1 Introduction.- 1.1 Object-Oriented Languages and Tools.- 1.2 Guidelines for the Design of a Graphics System.- 1.3 Overview.- 2 Object-Oriented Concepts.- 2.1 Objects and Messages.- 2.2 The Class.- 2.3 Message Passing.- 2.4 Inheritance.- 2.5 The Smalltalk-80 Programming Environment.- 2.6 Summary of the Basic Concepts.- 3 Object-Oriented Interface Architecture.- 3.1 Application Framework as Generic Application.- 3.2 The Model-View-Controller Triad.- 4 Smalltalk-80 Graphics Kernel.- 4.1 Output Primitives.- 4.2 Generation and Display of Graphics Objects.- 5 GKS and Object-Oriented System Design.- 5.1 Goals of Standardization.- 5.2 A Short Review of the Main GKS Features.- 5.3 The Structure of a GKS Program.- 5.4 Object-Oriented Modifications.- 5.5 Guidelines for an Object-Oriented Kernel.- 5.6 An Extended Layer Model.- 5.7 Assignment of Attributes.- 5.8 Summary.- 6 Graphics Part Hierarchies.- 6.1 Introduction.- 6.2 Part Hierarchies and Computer Graphics.- 6.3 MacDraw and Part Hierarchies.- 7 PHIGS and Part Hierarchies.- 7.1 Drawbacks of the GKS Model.- 7.2 Motivation for an Extended Functionality.- 7.3 PHIGS Components.- 7.4 Modeling Part Hierarchies in PHIGS.- 8 GEO++.- 8.1 Goals and Motivation.- 8.2 GEO++ Model.- 8.3 Functional Overview by an Example.- 9 Programming Examples.- 9.1 Office Layout Application Programmed With PHIGS.- 9.2 Office Layout Application in GEO++.- 9.3 Comparison of the PHIGS and GEO++ Solution.- 9.4 Pick Object and Assign Attribute.- 9.5 Higher Level Hierarchies.- 9.6 Interactive Editing of a PolyLine.- 9.7 Examination and Comments.- 10 Using Inheritance.- 10.1 Inheritance in GEO++.- 10.2 Alternative Naming.- 10.3 Construction of a Part Hierarchy with Predefined Slots.- 10.4 Using Call-Backs.- 10.5 Accessing Parts.- 11 Prototypes and Delegation.-11.1 What are Prototypes?.- 11.2 Relevance for Computer Graphics.- 11.3 A Prototype Model for GEO++.- 12 GEO++ in Smalltalk-80.- 12.1 Internal Representation of a Group.- 12.2 Implementation of Parts.- 13 Additional Concepts and Tools.- 13.1 Additional Semantical Concepts.- 13.2 Connectivity.- 13.3 Graphics Constraints.- 13.4 Adding Semantics to a Graphics Kernel.- 13.5 Graphics and Hybrid Knowledge Representation.- 13.6 Computer Graphics and Hybrid Systems.- 14 Towards an Object-Oriented Standard?.- 14.1 Chances for an Object-Oriented New API.- 14.2 Requirements and Problems.- 14.3 Guidelines.- References.