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Über dieses Buch

We have written this book principally for users and practitioners of computer graphics. In particular, system designers, independent software vendors, graphics system implementers, and application program developers need to understand the basic standards being put in place at the so-called Virtual Device Interface and how they relate to other industry standards, both formal and de facto. Secondarily, the book has been targetted at technical managers and advanced students who need some understanding of the graphics standards and how they fit together, along with a good overview of the Computer Graphics Interface (CGI) proposal and Computer Graphics Metafile (CGM) standard in particular. Part I, Chapters 1,2, and 3; Part II, Chapters 10 and 11; Part III, Chapters 15, 16, and 17; and some of the Appendices will be of special interest. Finally, these same sections will interest users in government and industry who are responsible for selecting, buying and installing commercial implementations of the standards. The CGM is already a US Federal Information Processing Standard (FIPS 126), and we expect the same status for the CGI when its development is completed and it receives formal approval by the standards-making bodies.

Inhaltsverzeichnis

Frontmatter

The Computer Graphics Interface

Frontmatter

Chapter 1. Introduction to Computer Graphics Standards

Abstract
Functional standards specify a model of a system, a set of operations on the model, and the externally visible effects of these operations. Such standards do not specify how these effects are to be implemented. In short, standards codify the exchange of information across an interface between two functional units and specify what is to be exchanged, but not how the functional units carry out their operations.
David B. Arnold, Peter R. Bono

Chapter 2. The Computer Graphics Interface

Abstract
The Computer Graphics Interface is a standard functional and syntactic specification for the exchange of device independent data and associated control information between systems with graphical functional capabilities. These systems may be peer graphics systems or may be device dependent graphics device drivers.
David B. Arnold, Peter R. Bono

Chapter 3. Elementary CGI Output and Attribute Functions

Abstract
Part 3 of the CGI describes the functions that define graphic objects. This includes both the primitives’ geometry and the attributes that affect the final rendering of the objects on the display surface. The Part also defines a few control functions provided specifically to affect the behaviour of the other functions in the Part. This is by far the largest Part of the CGI and many of the functions are identical or correspond closely to CGM functions.
David B. Arnold, Peter R. Bono

Chapter 4. Control and Error Handling

Abstract
Part 2 of the draft CGI standard covers the topics of Control, Negotiation, and Error Handling, and the functionality is grouped into four sections:
  • Virtual Device Management, concerned with managing the dialogue session and with global operations on the graphic image.
  • Coordinate Space Control, for establishing correct transmission of coordinate information and for management of the coordinate space.
  • Error Management, concerned with error detection, reporting, and reaction.
  • Miscellaneous Control.
David B. Arnold, Peter R. Bono

Chapter 5. The Raster Functions in the CGI

Abstract
The Raster functionality of the CGI provides the facilities to allow the client to create, store, manipulate, and display images defined as sets of pixels. Bitmaps provide the second point in the graphics pipeline (below segmentation) at which a snapshot of the graphics data, at a particular level of refinement, can be kept and manipulated. It represents a level of storage much farther down the pipeline than segmentation, at which stage many more of the indirect references implied in the functions used in the CGI have been converted to a viewable image. For example, by the time the definition of a polyline is stored in a bitmap, the information available at the CGI/client interface about the current settings of line width, etc., have been turned into instructions to set particular pixels in the bitmap.
David B. Arnold, Peter R. Bono

Chapter 6. Synchronous Input

Abstract
The input functionality of the draft CGI standard provides the sort of compatibility and consistency of approach that you would expect of the lowest level of standard in an integrated family of graphics standards. The CGI therefore adopts as a minimum the range of input classes used by the other members of the family of graphics standards (GKS, GKS-3D and PHIGS), operating in any of the modes catered for in those standards.
David B. Arnold, Peter R. Bono

Advanced Features of the CGI

Frontmatter

Chapter 7. Segmentation in CGI

Abstract
Segmentation is a well understood concept in computer graphics, having been a part of the expected functionality since virtually the start. However, perhaps because of this length of experience in using segments, there are actually many more variations than is generally realized. The basic concept is of a set of functions to control the storage, manipulation, and retrieval of collections of graphics primitives and associated attributes. Figure 7.1 shows a generalized graphics pipeline with three potential areas for the storage of graphical items.
David B. Arnold, Peter R. Bono

Chapter 8. Further CGI Output and Attribute Functions

Abstract
In Chap. 3 we saw how the primitives in the CGI are divided into five classes:
  • Line functions
  • A marker function
  • Text functions
  • Filled area functions
  • A cell array function.
David B. Arnold, Peter R. Bono

Chapter 9. Asynchronous Input

Abstract
In Chap. 6 we introduced the basic concepts of CGI input. All eight classes of input device were described along with the concepts of triggers, measures, echos, prompts, etc. The control of synchronous modes of operation-REQUEST and SAMPLE-was discussed. These modes are synchronous not only at the interface, which is a level at which all CGI functions are synchronous, but also from the perception of the operator of an interactive system using them.
David B. Arnold, Peter R. Bono

Chapter 10. CGI Conformance and Constituency Profiles

Abstract
Constituency profiles are an attempt to recognise that a very large number of “sensible” devices can be configured from various combinations of CGI functions and of different minimum capabilities and default values. Such constituency profiles are expected to be formulated by the constituency itself in most cases similarly to the way in which users in particular areas of CAD are beginning to get together to formulate profiles for CGM interpreters (see Chap. 16 and App. F). The draft CGI standard does contain the first attempt at constituency profiles for the GKS community. The definition of the profiles for GKS are given below.
David B. Arnold, Peter R. Bono

Chapter 11. Implementations of the CGI

Abstract
Strictly speaking, it is premature to discuss implementations of the CGI. The current version of the CGI standard is only at draft proposal stage, within both ANSI and ISO. (See Appendix C for a complete discussion of the stages of standardization and the standardization process.) Nevertheless, the CGI project has been underway within the US since 1981 and within ISO since 1984.
David B. Arnold, Peter R. Bono

The Computer Graphics Metafile

Frontmatter

Chapter 12. CGM Concepts and Purposes

Abstract
As we explained in Chap. 1, to exchange pictures among diverse applications and across separate programming environments, information can be captured at an interface and placed in a graphical metafile, a formatted disk or magnetic tape file containing graphical commands and data. These files can be transmitted over telephone lines and computer networks to be stored and processed at remote sites or reused locally as a library of predefined pictures.
David B. Arnold, Peter R. Bono

Chapter 13. CGM Elements

Abstract
Each instance of a Computer Graphics Metafile is a collection of elements drawn from the standardized set of elements listed in Table 13.1. Metafiles have a certain structure as illustrated by the state structure of a hypothetical CGM parser, shown in Fig. 13.1.
David B. Arnold, Peter R. Bono

Chapter 14. CGM Encodings

Abstract
The CGM standard consists of four parts: a Functional Description (Part 1), which describes the semantics of the CGM as explained in the previous chapter, and three standardized encodings of the CGM, which contain syntactic information only. These encodings are:
  • the Character Encoding (Part 2), which uses ASCII bytes, including control characters, to represent the element codes and parameters;
  • the Binary Encoding (Part 3), which uses internally formatted binary numbers to represent the data; and
  • the Clear Text Encoding (Part 4), which uses only the 94 printing characters from the ISO 646 7-bit code table to represent the data.
David B. Arnold, Peter R. Bono

Chapter 15. Relationship of the CGM to Other Standards

Abstract
CGI draws extensively for its model of a graphics picture on the CGM. It should be possible to generate a CGM through the CGI in a straightforward way. Consequently, all the CGM graphical primitive and attribute elements are present in the CGI. However, since the CGM was technically frozen, new primitive and attribute functions have been added to the CGI. Consequently, these functions need to be added as elements of the CGM. The CGM Addendum 1 project assigned to ISO/IEC JTC1/SC24 will add all those CGI functions, not yet in the CGM, that were considered to be technically frozen as of June, 1987.
David B. Arnold, Peter R. Bono

Chapter 16. Implementations of the CGM

Abstract
Although CGM was published in late 1986, already by the end of 1987 nearly two dozen companies in the United States had released products or announced plans for products incorporating support for the CGM.
David B. Arnold, Peter R. Bono

Chapter 17. Future Extensions to the CGM

Abstract
As soon as the CGM was technically frozen in late 1985, there was pressure from various graphics user communities to specify additional elements. The sources of pressure are widespread and reflect diverse needs. The commercial acceptance of the CGM, described in the previous chapter, is fueling the demands for greater capability.
David B. Arnold, Peter R. Bono

Backmatter

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