[winswitch] issue with forwarding x to a lower res monitor from a virtual Xvfb

Zenny garbytrash at gmail.com
Sun Nov 15 09:51:38 GMT 2015

On 11/15/15, Antoine Martin <antoine at nagafix.co.uk> wrote:
> On 15/11/15 14:44, Zenny wrote:
>> Hi,
>> xpra is very interesting, but I am encountering an issue or say cannot
>> figure out exactly how to achieve the following.
>> 1. Start a xvfb based virtual x instance in a resolution say 4k
>> (3840x2160) in one machine (server) with say libreoffice impress, and
>> broadcast using 'xpra shadow :10"
> Please include the exact command line used for starting the Xvfb and
> libreoffice.

$ Xvfb :10 -screen 0 4096x2160x24+32 -fbdir /var/tmp &
$ export DISPLAY=:10.1
$ libreoffice & / i3 & / lxsession -s LUBUNTU -e LXDE
$ xpra shadow :10

>> 2. Access that instance from another machine (laptop) using 'xpra
>> attach ssh:hostname:10'

$ xpra attach ssh:HOSTNAME:10

>> 3. Screencapture the :10 inside the same machine at 4K.
> Using which tool?

initially with ffmpeg and then with xwd / maim

>> But it does not allow me to capture in 4K but at the same resolution
>> as of the rendering laptop.
> I have tested here with Xdummy and that worked fine.

With Xdummy, once I attach to the remote machine with xpra, the ffmpeg
fails as it says "the capturing region lies out of the range." or
something like this.

>> I checked Xdummy related to Ubuntu instruction at
>> https://www.xpra.org/trac/wiki/Xdummy, but to no avail.
> Are you using Xvfb or Xdummy? What distribution and version?

Tried with Xvfb, didn't work and then with Xdummy. Still experimenting. ;-)

$ lsb_release -a
LSB Version:	core-2.0-amd64:core-2.0-noarch:core-3.0-amd64:core-3.0-noarch:core-3.1-amd64:core-3.1-noarch:core-3.2-amd64:core-3.2-noarch:core-4.0-amd64:core-4.0-noarch:core-4.1-amd64:core-4.1-noarch:security-4.0-amd64:security-4.0-noarch:security-4.1-amd64:security-4.1-noarch
Distributor ID:	Ubuntu
Description:	Ubuntu 14.04.3 LTS
Release:	14.04
Codename:	trusty

xpra  is at v0.15.8-2 and xvfb is at v1.15.1-0ubuntu2.7

>> Any hints would be highly appreciated. Thanks!
> You may also be interested in the following 0.16 features:
> * ability to NOT change the virtual display to match the client's
> resolution using:
> XPRA_RANDR=0 xpra start ...
> See:
> http://xpra.org/trac/changeset/11229
> Shadow mode is A LOT less efficient than the regular "start" mode.
> * desktop scaling, which allows you to upscale or downscale the server
> resolution when displayed on the client:
> http://xpra.org/trac/ticket/976
> So you could render at 4k and display at 2k for example (though the main
> purpose of this ticket is to do the opposite to save bandwidth).
> * "sync-xvfb" fix for screen capture tools:
> http://xpra.org/trac/ticket/988

Very interesting. Is there a binary of this dev release?

Thanks for taking time to reply.


> Cheers
> Antoine
>> Cheers,
>> /z
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