[winswitch] fakeXinerama questions

[Antoine Martin]

On 17/01/17 04:25, Lukas Haase via shifter-users wrote:
> Hi,
> 
> I have some questions regarding fakeXinerama. I use it in the following setup:
> 
> 1.) Client is a Win 10 laptop with 3 monitors attached:
> 1366x768      1920x1200        1920x1080
> 
> 2.) Ubuntu LTS Xenial Xerus with xpra running xpra.
> On the xpra server, I do not start the X client directly but use DISPLAY=:100 ssh -X otherserver
Do not use:
DISPLAY=:100 THECOMMAND
always use this form instead:
xpra --start=THECOMMAND
As this will survive if the connection is severed and ensure that the
environment is correct for the DISPLAY. There is more to it than just
$DISPLAY, for example: preloading fakeXinerama..

> 3.) otherserver is a RHEL5 linux system that runs proprietory software
> 
> Stated differently, I use xpra as a terminal server.
> Now if I want to use fakeXinerama, would I use it on the xpra server (preload it into ssh) or on the RHEL5 server (preload it into the proprietory applications) or would it not work at all?
When you run "ssh -X" the application that you start will be talking
directly to the X11 server on your Ubuntu system (via the ssh tunnel),
but since the application is running on a different system, in a
different environment, the fakeXinerama library will not be injected.

You would need to inject it by hand with LD_PRELOAD when you start your
proprietary application.
(that's assuming that you really need it - and you probably don't)

> My second question is regarding fakeXInerama in general. I still do not 100% understand what it really does.
> Which advantage does it give to me in the setup above?
I assume that you've read the wiki page here:
https://www.xpra.org/trac/wiki/FakeXinerama

> Ultimately what I could love is to let xpra IGNORE the first monitor (1366x768) and make it ONLY use the second two (1920x1200, 1920x1080). 
This is not xpra's job: xpra forwards the windows to the client OS (ie:
MS Windows 10 in this case), the client OS is in charge of placing the
windows where it sees fit.
You may be able to find a MS Windows tool that does this instead.

> I tried creating .100-fakexinerama with the following content (on the xpra server and starting xterm rather than "ssh -X"):
> 
> 
> # 2 monitors:
> 2
> # DISPLAY1
> 0 0 1920 1200
> # DISPLAY2
> 1920 0 1920 1080
> 
> However, I do not see any differences.
These settings would not actually match your display size and this could
cause problems. If anything, IF (a big if) the application used the
Xinerama data somehow, this could clamp the windows to the first two
monitors instead.

Also, you're not stating when you created that file - which may get
overwritten when the client connects. Applications tend not to reload
the Xinerama data.

> Does this even do what I want and if yes, what is the correct format?
No, fakeXinerama is not the solution you are looking for.

Cheers
Antoine

> 
> Thanks!
> Lukas
> 
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