“Graphics standardization” by Hagen

  • ©Paul ten Hagen




    Graphics standardization



    The big challenge for a graphics standardization project is to realise a truly device independent graphics package which nevertheless allows for unrestricted use of facilities offered by a particular device. In 1980, it was reported at a SIGGRAPH session that the Graphics Working Group of ISO (ISO/TC97/SC5/WG2) had decided to define a 2D core-like standard based on the DIN GKS proposal. At the same session, a new concept was introduced called a workstation, which was to be a basis for achieving device independence in GKS. In the two years of reviewing which has since taken place, the workstation concept has been further developed and as a result has become much more important than it was, say, in the 1979 version of GKS. The workstation supports a two stage abstraction mechanism for input and output primitives, especially with respect to their attributes (including transformations). In this way, every aspect which can be dealt with in a similar manner for each device (e.g. purely geometric information) is moved up to the higher abstraction level and called workstation independent. Aspects with a limited device independence, which apply only to certain classes of devices (e.g. colour) are in the lower level of abstraction and are called workstation dependent. Following this two level abstraction, a two level mapping is defined in GKS, leading to two classes of functions: those addressing all active workstations at the same time (w.s. independent) and those addressing a particular work station (identified by a parameter). Workstations are now allowed to differ in the value ranges for the attributes they support. The two-level mapping provides setting of an abstract primitive attribute which is next either applied on the same abstract level, or subsequently mapped on the most appropriate value available for each individual workstation. The second mapping can also be controlled by workstation functions. In this way, two workstations can, for example, provide a different presentation of the same abstract picture simply by selecting different representations for various attributes (e.g. quick and dirty versus high quality). Moreover, they can also provide a “best likeness” picture by selecting an appropriate combination of attributes with the same visual effect (for example, each workstation may provide different means for generating the same text-font). It will be illustrated why this uniform scheme for a two level attribute mechanism was to be developed beyong current practice in order to get a satisfactory solution for device independence. A further basic facility derived from the workstation concept is the ability to configure a workstation out of abstract devices (i.e. 0 or 1 output plus 0 or more input devices). Most input devices depend for their user feedback, on the output devices available. All inputs that need the same output device are now integrated into one work station. Again, the two level structure is very helpful. All configuration aspects of providing prompts and echoes are local to the workstation. They can be controlled via abstract functions which are mapped on physical realisation at the workstation. Echoes and prompts as well as other aspects for input are treated like workstation dependent attributes. Here also, the ISO reviewing process has brought about new concepts and methods which will be presented and illustrated in this session. The European members of ISO especially, are very satisfied with these achievements and are developing further on the basis of GKS.

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