GKS Descriptions

The workstation description file only needs to be modified if a new device type is supported by GKS so this section will only be of interest to someone adding a new workstation handler.

The workstation description table is stored in a binary file gns_gksdevices (located in a similar way to the names files). This binary file is built from a text version of the description table by running the program gksbuild. (gksbuild is not normally installed and must be created by re-building the gns libary.)

The description table distributed with the system contains an entry for every workstation type supported by GKS-UK and is built from the text file gksdevices.txt which can be used as a template for any changes or additions.

The text file looks something like:

      WORKSTATION = 10
         CLASS = METAFILE_INPUT
         OUTPUT =  FILE
      WORKSTATION = 50
         CLASS = METAFILE_OUTPUT
         OUTPUT = FILE
      WORKSTATION = 101
         CLASS = TERMINAL
         SCALE = 3.3833E-4
         OUTPUT = DIRECT
         CLEAR = SELECTIVE

Each workstation description starts with WORKSTATION = type and contains a list of statements of the form keyword = value.

The value field takes one of the following forms:

Integer

A decimal integer.

Real

A real number constructed according to the usual FORTRAN rules but without any imbedded spaces.

Keyword

A character keyword.

Character string

A character string delimited by the first non-space character following the equals sign and the next occurrence of that same character. When character strings are being interpreted the ^ character is used as an ``escape'' character for inserting control characters (e.g. control Z (ASCII 26) is represented by ^Z). A literal ^ character is represented by ^^.

The only mandatory keyword is CLASS which indicates to which category of device the workstation belongs and must have one of the following keywords as its value:

GRAPHICS_OVERLAY
IMAGE_DISPLAY
IMAGE_OVERLAY
MATRIX_PRINTER
METAFILE_INPUT
METAFILE_OUTPUT
PEN_PLOTTER
TERMINAL
WINDOW
WINDOW_OVERLAY

For all workstation types other than those of class TERMINAL, METAFILE_INPUT and METAFILE_OUTPUT the keyword DEFAULT_NAME is also mandatory. The value must be the name of the device used when the workstation is opened with a connection identifier of 0. For devices of class TERMINAL the logged-on terminal is used in these circumstances.

Other keywords describe such things as the approximate size of ``device units'' and a character string that can be used to clear the text screen of a terminal.

A complete list of all the keywords that can appear in the description file can be found in this appendix.