17.1 Kind of graphics servers
The basic idea behind the scene is that there is only one program (the server)
permanently active which knows how to plot in a device-dependent manner, and
that all user plotting commands (the clients) just communicate with the server
via a communication channel using a limited set
of standard (binary) commands corresponding to graphics primitives.
There are two main flavours of servers currently available in XAS, each of
which may exist in several instances.
X-window server (xw)
The X-window (X11) server is the one commonly used for interactive plotting. Each
server instance (e.g. xw1, xw2, etc.) keeps alive on the screen
a graphics window.
Both vector plots and images can be displayed.
The user may interact with the graphics using the mouse.
There are three sub-flavours of PostScript servers (they actually share a single
executables and differ only in the PostScript macros invoked for some operations).
These servers are not interactive, and have been tested and developed only in a
They write to a cyclic pool of files file00.ps to file99.ps in
Black & White PostScript server (bw)
This server (whose instances are named bw1, bw2, etc.) produces
black and white (including gray scale images) plots.
Colour PostScript server (cp)
This server (whose instances are named cp1, cp2, etc.) produces
colour plots using PostScript Level 1 features.
Colour Level 2 PostScript server (c2)
This server (whose instances are named c21, c22, etc.) produces
colour plots using PostScript Level 2 features (essentially this means that
colour images can be three times smaller).