This International Standard specifies a set of functions for computer graphics programming, the Graphical Kernel System for Three Dimensions (GKS-3D). GKS-3D is a basic graphics system for applications that produce computer generated three dimensional pictures on graphics output devices. It supports operator input and interaction by supplying basic functions for graphical input and pic-ture segmentation. It allows storage and dynamic modification of pictures. A fundamental concept in GKS-3D is the workstation, consisting of a number of input devices and a single output device. Several workstations can be used simultaneously. The application program is allowed to adapt its behaviour at a workstation to make best use of workstation capabilities. This International Standard includes functions for storage on and retrieval from an external graphics filé. Also, the functions are organized in upward compatible levels with increasing capabilities.
This International Standard provides application programs with the capability to define and display 3D graphical primitives, specified using 3D coordinates. In addition, the GKS-3D input model provides 3D locator and stroke input.
The output primitives of this International Standard differ from the output primitives of ISO 7942 in the following ways:
a) the polyline and polymarker primitives are defined by an arbitrary sequence of 3D coordinates;
b) the text, fill area and cell array primitives remain planar, but may lie in a plane positioned arbitrarily in 3D space;
c) the nll area set primitive is introduced.
Functions are provided in this International Standard to generate these primitives.
The functions of ISO 7942 can be used in this International Standard. However, the output functions generate instances of 3D primitives — instances that are constrained to lie in a plane. Furthermore, additional capabilities are provided in this International Standard to:
d) specify views of 3D objects;
e) obtain information from 3D input devices;
f) permit workstations to perform hidden line/hidden surface removal (HLHSR).
This International Standard provides no specific functions for controlling such rendering tech-niques as Ught source, shading, texturing, and shadow computations. However, workstations may apply these techniques, locally as the primitives and attributes are realized, provided that the general guidelines of Annex D concerning allowable workstation differences are followed.
NOTE - For certain parameters of the functions, GKS-3D defines value ranges as being reserved for registration (see 4.1.2). The meanings of these values wiU be defmed using the established procedures.
GKS-3D defines a language independent nucleus of a graphics system. For integration into a programming language, GKS-3D is embedded in a language dependent layer obeying the partic-ular conventions of that language.