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From: kobuchi%hoover.DECnet@win1.ims.abb.COM ("HOOVER::KOBUCHI")
Newsgroups: comp.windows.x
Subject: DECwindows DisplayString
Message-ID: <9101222319.AA10945@uc.msc.edu>
Date: 22 Jan 91 23:19:00 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 62

OK, hope this message gets through OK--this is my first attempt at sending a
message to any Internet address...

I've just encountered a problem with obtaining the display name, using
DisplayString.  We just upgraded our VAXes to VMS 5.4.  In this upgrade, DEC
changed DECwindows so that DisplayString returns a VAX/VMS device name instead
of a string like "nodename::0.0".  This change caused my code to fail and the
only way I can think of to fix my code seems to be extremely un-X.

Basically, my DECwindows code is designed to use two CRTs (when available). 
I'm currently using a VAXstation 3100 with a color monitor and a black and
white monitor.

The first thing my code does is to open a temporary connection and determine
how many monitors are on the workstation:

            display = XOpenDisplay("");
            num_screens = ScreenCount(display);

It then gets and stores the display name so I can use the name to open up
connections to each screen (monitor) on the workstation:

            display_name = DisplayString(display);

I then close this temporary connection:

            XCloseDisplay(display);

Then I start doing the DECwindows initialization stuff:

            XtToolkitInitialize();
            app_context = XtCreateApplicationContext();

Finally, I enter a loop for each screen (monitor) on the workstation and I open
a connection for each screen using XtOpenDisplay.

Now this is where I use the display name I got beforehand: every time I call
XtOpenDisplay, I give it the display name with the last character modified to
be the screen number.

For example, if the workstation's node name is NODE1, and it has two screens, I
call XtOpenDisplay twice, the first time giving it the display name of
"NODE1::0.0" and the second time giving it the display name of "NODE1::0.1".

This used to work on VMS 5.3: DisplayString would return the string
"NODE1::0.0".

Now, on VMS 5.4, DisplayString returns a string containing a VAX/VMS device
name like "WSA1:".  Well, ok, I've found out that I can use this device name by
appending the server number and screen number to it (e.g., "WSA1:0.0"), but it
doesn't look like X anymore.  Also, I don't think I can determine the actual
node name anymore (so I could include it in messages to the user).


Did DEC screw up?  Did I screw up?  Is this the "correct" way to handle
multiple monitors on a single workstation?


Kent Kobuchi
ABB Engineering Automation
Internet: kobuchi%pasceg.decnet@win1.ims.abb.com
Voice:    (415) 748-4791