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

Antoine Martin antoine at nagafix.co.uk
Thu Nov 19 16:14:11 GMT 2015

On 17/11/15 20:25, Zenny wrote:
> Thanks again.
> The only bottleneck remained is refreshing the display in the client
> (not matter which encoding or quality is used).  Please note that it
> is with Xvfb (not Xdummy). When display change takes place, say a
> slide in libreoffice impress, only a quarter of display changes in
> client running at (1920x1080), while the screecapture from the virtual
> X server running in 4K is okay.
> I start xpra server like:
> $ XPRA_RANDR=0 xpra start --use-display :10 --sync-xvfb=50
> --bind-tcp=localhost:10000
> and xpra client like:
> $ xpra attach tcp:localhost:10000:10 --desktop-scaling=0.5
> --sync-xvfb=50 --opengl=no --encoding=jpeg --quality=85
> Appreciate if there is any inputs on automatically refresh the full
> screen (not just quarter of the screen) in xpra client.
Just a final message to close this thread - I hope.
We continued to debug this issue in a ticket:

And the requested feature now works as expected, even with OpenGL 
disabled, etc.
The important points being:
* a recent 0.16 build is required for the features below (and a few bugs 
were found in the process)
* "XPRA_RANDR=0" to keep the server's Xvfb at its starting resolution 
(or you have to ensure the desktop-scaling value will give the desired 
resolution on the server side)
* "sync-xvfb" enabled to actually paint window updates on the virtual screen
* "desktop-scaling" to make the server's screen size fit on to the client


> Thanks,
> /z
> On 11/17/15, Antoine Martin <antoine at nagafix.co.uk> wrote:
>> On 16/11/15 23:51, Zenny 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.
>> If you know your client's resolution before you connect, you can
>> calculate the ratio which will give you 4k on the server.
>> It just won't handle monitor hotplugging.
>> Antoine
>>> Thanks again,
>>> /z
>>>> Antoine

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