From: hersh@expo.lcs.mit.edu (Jay Hersh)
Newsgroups: comp.windows.x.pex
Subject: Re: PEX subsets
Keywords: PEX subset PHIGS workstation immediate structure enquiry
Date: 12 Aug 92 18:04:03 GMT
Organization: X Consortium, MIT Laboratory for Computer Science

lilleyc@cs.man.ac.uk (Chris Lilley) writes:

>Hi

>How does one find which of the three subsets a given PEX server
>supports? I am looking for a short program to tell me. Also, how to
>tell if a server is 5.0 or 5.1

All this information is available from the Get Extension Info request.
If you're a PEXlib user or will be then this is simple to do.
If you're using PHIGS, then you will need to generate the request yourself
or get hold of another API or toolkit which might provide this for you.


>Reason I ask: we have a VAXstation here running PEX. It displays DEC
>phiga apps to either an X or a PEX workstation (ie workststion types
>231 or 241, for Motif).  As far as DEC PHIGS is concerned, PEX is
>there and able to support server-side structures (that is, indeed, the
>default). DEC PHIGS generates PEX 5.0 protocol.

you mean a vaxstation running a PEX Server. DEC PHIGS does not use 
the workstation subsets. Support for server side structure is not
the same as workstation support. There are 3 subsets, immediate
which means immediate mode graphics only, structure rendering, which 
means the server can store and render structures but not via a 
PHIGS workstation, and workstation, which means that structures 
can be stored and then posted to PHIGS woprkstations present on the
server. In DEC PHIGS the workstation stuff for PHIGS is actually
done on the client side. DEC does not support workstations in their
servers. I think there is probably some confusing nomenclature going
on here.

>We recently tried to display output from SunPHIGS 2.0 which claims to
>support PEX when present. This failed with an error message which
>apparently means that the PHIGS workstation subset is not present.

Does SunPHIGS know how to talk to non-workstation subset servers.
I don't think so. I thought the PEX-SI PHIGS knew how to do this, but 
we've found at least one bug trying this, and haven't had time to
trackit down further. You need to get Sun to support immediate mode
renderers if you wnat to work across from Suns to DEC. I believe
at some point in the future Sun will be adding immediate mode to
their servers, so at least your DEC apps should be able to talk to
the Sun servers.


>A demo program which came with a Tektronix XP29P PEX terminal we are
>looking at also failed with the same error. This program supports 5.1
>protocol.

>Could someone give me a quick summary or low-down on PEX subsets, how
>to get around the above problem and (preferably) why PEX has three
>subsets. Is this not going to be a bit of a problem in the future?

See above. Basically it appears 2 things need to happen. The first
is that the one vendor who only supports Workstations needs to 
get a product out that has immediate mode support. Then all the
vendors will at least have immediate mode. Then all the vendors
need to provide a fallback in their client side PHIGS libraries 
to do workstations via immediate mode. Of course getting the one
vendor who doesn't support workstation mode to support it in 
their server as well would also help address the problem.

>Also could someone give me the email address of the PEX
>interoperability centre as I have some other stuff I would like to
>share with them.

pexic-pub-tech@convex.com



	Jay Hersh
	(personal oninions not representative of MIT)
--
Hopfen und Malz, Gott erhalts