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

Antoine Martin antoine at nagafix.co.uk
Tue Nov 17 04:40:37 GMT 2015

On 17/11/15 00:41, Zenny wrote:
> Okay, what I did was:
> On the xpra server:
> $ Xvfb :10 -screen 0 3840x2160x24+32 -fbdir /var/tmp &
> $ export DISPLAY=:10
> $ xterm && leafpad &
> On the client:
> $ XPRA_RANDR=0 xpra start --use-display :10
> Only disabling OpenGL allowed to render opened windows.
AFAIK, Xvfb does not support OpenGL.
And if you use Xdummy, you often need to use VirtualGL:
> However, other
> options in the xpra menu like Encodings, Quality and Speed are greyed
> out and cannot be changed.
That's because they are meaningless in this case as you are probably 
using mmap.
This can be seen in your server log file.
> On the server:
> $ ffmpeg -f x11grab -s 3840x2160 -i :10 -r 24 -deadline realtimeb:v 1M
> -threads 5 -qmin 0 -qmax 50 -crf 5 -preset ultrafast -f matroska
> 4k_screencap_xpra.mpv
>   The screencapture shows everything black including changes made in
> the xpra attached windows except cursors movements are captured.
> Any hint why the capture is not displaying the contents of the windows
> other than mouse movements?
Since you are not using "sync-xvfb", the xvfb will remain black.

This thread now almost has as many posts as the mailing list has had in 
September and October combined.
Please slow down, read the manual, the wiki and the links provided.

> Thanks!
> /z
> On 11/16/15, Zenny <garbytrash at gmail.com> wrote:
>> On 11/16/15, Antoine Martin <antoine at nagafix.co.uk> wrote:
>>>>> If you are certain that you will only need a single resolution, then
>>>>> you
>>>>> could also use a customized xorg.conf
>>>>> The "desktop-scaling" option in 0.16 looks easier to me than either of
>>>>> those options.
>>>> any man pages about desktop-scaling?
>>> Can you please check before asking?
>>> man xpra
>>> And also here (the second link on the wiki):
>>> http://xpra.org/manual.html
>> Sorry I skipped the part in the man-page. Still I could not figure out
>> the sync-xvfb part in the man pages.
>> After reading the --desktop-scaling part, the parameter allows to
>> control the server's x resolution on the fly.
>> But I am trying to do the other way round. The server's virtual X
>> remains at the 4K resolution while the client's varies according to
>> the physical screen attached.
>> Thanks again,
>> /z
>>> Antoine

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