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Multiple x screens and plasma/sddm
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allistarM
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Joined: 22 Jul 2004
Posts: 78

PostPosted: Tue Oct 17, 2017 3:07 am    Post subject: Multiple x screens and plasma/sddm Reply with quote

Hi all,
I have two Nvidia GeForce GTX 750 Ti GPUs in my computer. I have had a four screen setup for some time now and this works very well using Nvidia twinview with Plasma, SDDM and compiz-fusion for 3D effects. I want to add two more LCDs to this by utilising the second GPU. I know I cannot have those two additional screens "join" the same xscreen as the other four as my setup doesn't support SLI or Nvidia mosaic. That doesn't bother me too much. I can set up a different xscreen for the other two monitors but Plasma/sddm insists on starting on them when I do "/etc/init.d/xdm start" and this causes issues (plasmashell crashes on one of the other four monitors and is blank on the two new monitors). I think having multiple xscreens confuses Plasma/SDDM. I accept that I probably can't run Plasma on the second xscreen. What I would like is Plasma/SDDM running on xscreen 0 (four monitors) and e16 running on xscreen 1 (two monitors).

How do I convince xorg to start SDDM on xscreen 0 and e16 on xscreen 1?

Thanks,
Allistar.
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nativemad
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Joined: 30 Aug 2004
Posts: 903
Location: Switzerland

PostPosted: Tue Oct 17, 2017 3:37 pm    Post subject: Reply with quote

Hi

I've got 6 monitors working (2xnvidia [without SLI or such], 1xintel gpu with 2 monitors on each card) working on sddm/plasma via xinerama. I could share my xorg.conf if you like?! -But be warned, it is also not perfect in regards to opengl... :roll:
You could probably make two different xorg.conf files and start the second X with the -config option!?
How many display ports do you have/use per card?

Cheers
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allistarM
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Joined: 22 Jul 2004
Posts: 78

PostPosted: Tue Oct 17, 2017 7:08 pm    Post subject: Reply with quote

Hi,
Thanks for the offer. I don't want to be without the 3D effects etc that Compiz brings, so Xinerama is not an option for me. I'm ok with a solution of separate x-screens. I'm struggling to get sddm confined to x-screen 0 to allow me to run e16 (or something else) on x-screen 1.

Thanks again,
Allistar.
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nativemad
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Joined: 30 Aug 2004
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Location: Switzerland

PostPosted: Tue Oct 17, 2017 8:14 pm    Post subject: Reply with quote

Just configure your normal xorg.conf to only use screen 0-3. Then create a seperate xorg.conf for the other two screens.
Then via the xdm service, sddm should start on the first 4 screens.
Then you could start X manually with the other xorg.conf and put it in the background to test.
Code:
X -config /path/to/file &

If X is there, you should be able to startx things there like
Code:
DISPLAY=:1 xterm &


I don't know if e16 provides a "starte6" or similar, but look at /usr/bin/startx for reference on how to automate these steps... :wink:
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allistarM
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PostPosted: Thu Oct 19, 2017 3:59 am    Post subject: Reply with quote

Thanks, I think you're onto something. The only way I can structure this so that SDDM/plasma doesn't start up on xscreen1 is for xscreen1 to not exist when I run "startx". Forcing "exev startkde" to start only on display ":0.0" doesn't work, it seems to ignore this.

An issue with starting up another X on screen 1 is how to I set the position in real space between screen 0 and screen 1? That is, when I move my mouse off the edge of one of the screen 0 monitors it needs to enter the screen 1 monitor.
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nativemad
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PostPosted: Thu Oct 19, 2017 5:27 am    Post subject: Reply with quote

Yeah, I also got the feeling that KDE is doing a bit too much guessing by its own and almost gave up on it on my 6-screen setup. :roll:

What you could probably use for the pointer/keyboard dilemma would be synergy. But I never used it myself, so I don't know if it works "on the same host"...!?
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allistarM
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PostPosted: Fri Oct 20, 2017 4:15 am    Post subject: Reply with quote

I have an acceptable workaround. I have discovered that if I constrain compiz-fusion to one display and I run this twice (one on :0.0 and one on :0.1) then sddm/plasma doesn't get in the way on screen :0.1. I can than start up any apps from a shortcut (setting DISPLAY=":0.1" first) and the appear on xscreen 1. The downside is that xscreen 1 doesn't have a desktop manager running so there's no task bar. I'll investigate using something like lxdocker for this.

I can also move the mouse between screen 0 and screen 1 (although only when setting the position to be LeftOf/RightOf etc, this doesn't work when the position is Absolute). X doesn't seem fully capable of handling non rectangular screen layouts, but it's good enough for now.
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nativemad
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PostPosted: Fri Oct 20, 2017 4:54 am    Post subject: Reply with quote

Lol, nice workaraound! :P
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