Editing Graphics development with vplot (section)

==Frontend, and doing it yourself==
The system-user interface is split among three routines, which together
are called the "frontend".

Main_vplot is responsible for finding the input files and opening them,
deciding where the output should go for devices that aren't strong-willed
enough to insist on figuring it out for themselves, setting up signal
catching, interfacing with SEPlib, and doing self-documentation.
It also calls the other 2 routines, init_vplot and proc_vplot.

Init_vplot initializes all variables and calls dev.open to open the
device.

Proc_vplot processes the input files.

It is possible to skip main_vplot and call init_vplot and proc_vplot
yourself directly. However, init_vplot and proc_vplot expect certain
things to be set before they are called.

Init_vplot expects:

Xargc and xargv are just copies of main's argc and argv, but declared
globally so that other routines (namely getpar) have access to them.
Xargc and xargv should be declared in the calling program.

Callname is a string which gives the "pen filter name" of the set of
device-dependent routines you want. It should have the path stripped.
The device-dependent code may want to know callname in order to pick
between similar devices. Callname should be declared external.

Pltout is just a copy of stdout. It is an external FILE *.

Proc_vplot expects:

Infileno gives the number of input files. It is an external integer.

Pltinname[infileno] gives the names of the input files. It is
an external array of pointers to chars.

Pltinarray[infileno] gives the already-open stream pointers for the
afore-mentioned files. It is an external array of FILE *'s.

That's it.
It is also possible to bypass even calling proc_vplot. See sample.c
in .../vplot/filters for an example of how to do this.