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From: miner@ulowell.UUCP
Newsgroups: comp.graphics
Subject: Re: GKS, Postscript questions (summary needed)
Message-ID: <1047@ulowell.cs.ulowell.edu>
Date: Sun, 15-Feb-87 12:39:41 EST
Article-I.D.: ulowell.1047
Posted: Sun Feb 15 12:39:41 1987
Date-Received: Sun, 15-Feb-87 23:08:53 EST
References: <1049@uwmacc.UUCP>
Reply-To: miner@ulowell.cs.ulowell.edu (Richard Miner)
Organization: University of Lowell
Lines: 37
Keywords: GKS postscript

In article <1049@uwmacc.UUCP> jwp@uwmacc.UUCP (Jeffrey W Percival) writes:
> Now, the GKS calls produce some generic information
>(is this the VDI?) that is interpreted by "drivers", right?
Most implementations of GKS have a workstation layer below the GKS layer.
This is sometimes referred to as a Virtual Device Interface (VDI- CGI). It is
not necessarily interpreted by the device drivers.  In our implementation,
for example, the VDI level is implemented as a set of functions.  GKS mapped
and normalized data and attributes are passed from the GKS level to the
VDI level where they are then mapped to a specific device using information
in a virtual device table (VDT) and passed to the device driver. 

>A driver can go from VDI to, say, a TEK4014 or a Versatec.
Yes, or a GKS could be implemented to communicate directly to a TEK4014, not
very portable, but this is how many companies got GKS support in the old days.

>It could also go from VDI to a metafile.  Is this metacode
>part of the standard?  
While meta files are required by GKS there have been a few evolving standards
in the past which makes moving meta-files between different implementations of
GKS difficult.  GKSM was an originally proposed metafile format.  Most people
are now adopting CGM, Computer Graphics Metafile, which is becoming (or has
recently become) an ANSI standard metafile format. 

>See, we have a GKS package from a vendor, without a postscript driver.
>We also have a postscript printer.  Do we need a whole new GKS....
If you have information on your GKS's metafile format then it should
be a straight forward, but nontrivial, task to write a postscript conversion
utility.

>Any GKS packages out there with postscript support?
The GKS group at ULowell has plans to eventually write a postscript driver 
for their GKS.  In the meantime, since source is distributed with the system,
it is quite possible that some GKS-UL users will write the driver before 
the Ulowell team gets to it.

-- 
Rich Miner !ulowell!miner Cntr for Productivity Enhancement 617-452-5000x2693