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Re: [XForms] Determine Screen Sizes

From: jon
Subject: Re: [XForms] Determine Screen Sizes
Date: Mon, 17 Nov 2014 02:06:05 +0000

On Mon, 2014-11-17 at 01:10 +0100, Jens Thoms Toerring wrote:
> On Sun, Nov 16, 2014 at 08:08:05PM +0000, jon wrote:
> > From memory X has two ways it can treat multiple monitors. Most setups
> > are configured as one display of "monitor" times the width.  IE two
> > 1920x1080 (like I am using here) is one 3840x1920 display.
> And as Serge pointed out, when the heights are different the
> height of the larger monitor "wins".
> If I'm not completely mistaken, monitors can also "logically"
> be arranged to appear on top of each other. In that case I
> would expect that one will receive the added height of both
> and the width of the wider monitor...
> > But it is possible to have X treat them as separate displays, in that
> > case X display ":0" would be 1920x1080 as would display ":1"
> In that case I think XForms would only be able to use one of
> the monitors - one of them is probably the default one, i.e.
> what's set in the DISPLAY environment variable, and that
> would be used unless the program would be started with X
> '-display' option set to the other display for the second
> monitor (but then the first monitor will not be used).
> I don't know if there are any toolkits where you can set a
> display for a certain window of the application and another
> display for another window. While I have some dark memories
> of a 2-person game I played about 20 years where you could
> specify a display for the opponents screen I have no idea
> how this was done. Perhaps it was a script that started two
> instances of the game on different displays, both connected
> to a common server process, or if it was handled on the X11
> level, opening 2 displays at once (not many toolkits avai-
> lable back then - Motif was IIRC basically the only choice
> but very expensive, so people tended to program against the
> Xlib directly;-)

<Little off topic for list, sorry>

Some processes respect -display option, but if not you can specify the
display that the 'next' shell reference will open with "export DISPLAY="
from bash, the 'DISPLAY' eviron variable is will become the "server"
argument of the next XOpenDisplay() reference.

My shell gives.

# echo $DISPLAY

I think a second monitor would be  ":0.1" but i've always been a little
hazy on the syntax.  ":" on its own uses domain socket rather tcp
socket, "hostname:" uses tcp, but most modern distros start X with
-notcp.  "ssh -X" does something nasty at sockets level and sets the
DISPLAY variable.....

ssh -X <local IP>

address@hidden:~$ echo $DISPLAY


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