/**********************************************************************
*
*    README
*    ======
*
*    This README-file includes information about
*    the Varkon plotter/printer "filters/drivers".
*
*    (C)rebro University 2003-03-20    http://www.oru.se/tech/cad
*
***********************************************************************/

Plotting or printing is the process of copying some or all
of the graphics from your display onto paper. The word
"printing" is usually used for normal desk printers like a
postscript or HP laser. The word "plotting" is sometimes
used for bigger size dedicated plotting devices like a
HP pen plotter ot Gerber photo plotter. From Varkon's
point of view "printing" or "plotting" is no different
and both words are used to indicate the same thing.

Plotting/printing in Varkon is a 3-step process. If you use
any of Varkon's interactive functions for plotting (like
"autoplot") these 3 steps are done automatically and at once.
If you want to do it yourself this is what you need to do:

1. First you create a plotfile.

2. Then you convert the format of the plotfile to a
   format suitable for a specific plotter or printer. 
   This is where the PL module is involved.

3. Finally you send the formatted data to the plotter or printer.
   This usually involves using the spooler system of your computer
   but you could also send the data to a device directly connected
   to a serial or parallell port.

Exactly how this process works depends on the platform you
are using and how your platform is configurated. UNIX for
example is different from Windows95/98/NT.

Step 1 is the same on all platforms. Varkon includes several
interactive functions as well as support in MBS to create
plotfiles. A Varkon plotfile is an ASCII text formatted file
with an ISO-GKS Metafile representation of the image you want
to plot. Varkon uses the file extension ".PLT" for plotfiles.
This format is device independant and Varkon uses the
same format on all supported platforms so you can create PLT-
files on one platform and send them over a network for processing
on another platform.

Step 2 and 3 are different on different platforms. With Windows, Varkon
uses msw32.dll to convert the PLT-file to Windows commands and send
them to the Windows spooler system for output. The Windows graphics
system takes care of the conversion needed for the actual device you
are using. This means that with the Windows version of Varkon you
normally only need msw32.dll to get your graphics out on paper.

UNIX is slightly different. If you have a postscript printer or
emulator (ie. ghostscript) you can use the postscript filter
to convert PLT-files into postscript files. If you dont want to
use postscript there are several other filters supplied in the
PL module. In any case what you need to do is to filter the
contents of the PLT-file into the format you want to use, ie.

   postscript -options < my_plotfile.PLT > my_plotfile.ps

if you want to use postscript, or

  hpcl5 -options < my_plotfile.PLT > my_plotfile.hpcl

if you have a HP laser printer.

When the PLT-file is converted to the right format all you have
to do is to send it to the printer or plotter. You can use the
spooler to do this, ie.

   lpr my_plotfile.ps

or you can send it directly to a specific port

   cat my_plotfile.ps >/dev/tty0

How to set up a spooled printer or how to configure handshaking etc.
for a port will differ on different platforms and is not covered
in this README.

If none of the supplied filters work with your hardware it's
usually quite easy to write a new one. What you need to do is
to write an init, exit, pen_up/move, pen_down/move, select_pen and 
set_linewidth function for your printer. The rest is taken care
of by PL. Have a look at the supplied filters (hp7475.c is rather
well commented) and use one of them as a template. If you get it
working and want to share it, please send it to us so we can merge
it into the source distribution.

/**********************************************************************/
