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From: webber@brandx.rutgers.edu (Webber)
Newsgroups: comp.graphics
Subject: Re: General questions on GKS, interactive graphics for VAX/VMS
Message-ID: <558@brandx.rutgers.edu>
Date: Sun, 8-Nov-87 03:23:30 EST
Article-I.D.: brandx.558
Posted: Sun Nov  8 03:23:30 1987
Date-Received: Tue, 10-Nov-87 06:44:02 EST
References: <846@sdcc12.ucsd.EDU>
Organization: Rutgers Univ., New Brunswick, N.J.
Lines: 39
Keywords: GKS graphics VAX VMS interactive
Summary: short answer plus reference

In article <846@sdcc12.ucsd.EDU>, gr47@sdcc12.ucsd.EDU (gr47) writes:
> ...
> Where can I find out what the different levels of GKS correspond to
> in practical terms?  I am particularly interested in a package
> written at U. Lowell, MA that conforms to level 2A.  Can someone give
> me a quick rundown on 2A and/or some refs to GKS level descriptions? 

Assuming you don't want to read the standard itself (ANSI standard
X3.124 - 1985; American National Standards Institute; 1430 Broadway;
New York, N.Y. 10018; 212-354-3300), probably the next best thing
is ``Computer Graphics Programming: GKS - The Graphics Standard''
(by G. Enderle, K. Kansy, and G. Pfaff; Springer-Verlag).

The basic level scheme in GKS works along two dimensions, input and output.
So, ``2a'' means level ``2'' output and level ``a'' input. 

Roughly, level ``0'' output means that you can use the system as an
output interface, but it doesn't keep track of what you have done.
Level ``1'' output means that the system keeps linked lists of
primitives (called segments), which you can then later refer to to do
things like rotation.  Level ``2'' output means that the segment
memory of level ``1'' can now be shared among workstations (allowing
multiple workstation systems to be run).

Roughly, level ``a'' input means no input primitives.  Level ``b''
input means that input is upon request only (similar to UNIX
getchar()).  Level ``c'' input means that input events and sampling is
supported (which means that the system is now tracking the input and
answering queries from the application about the state of what has
happened on various input devices).

In a more general setting, GKS and other graphics standards are discussed
in ``Raster Graphics Handbook, 2nd Edition'' (by Conrac Division/Conrac
Corporation; Van Nostrand Reinhold Company).  Also of general interest
is the booklet ``Standards in the Computer Graphics Industry'' (prepared
and sold by: National Computer Graphics Association; 2722 Merrilee Drive;
Suite 200;  Fairfax, VA 22031).

------- BOB (webber@aramis.rutgers.edu ; rutgers!aramis.rutgers.edu!webber)