vnc server not refreshing picture

[Timo Kaufmann]

Hi!

I am starting a vnc server on a virtual X display (trying to extend my monitor). When I connect to that server (tried multiple clients), everything will be frozen. The image will only refresh when I do something on the "real" monitor, like open a new window (or when I run `xrefresh`). That seems to force the refresh and the vnc reviewer "advances" one frame.

That sounds like the vnc server doesn't poll, but it even happens with `-pollingcycle 1`.

The problem does not occur when using x11vnc instead.

Here's the exact script used to setup the virtual display and start the server:
https://gist.github.com/timokau/5e2eb60c3452d11d2e6f30b82c8b48af

Does anybody have any idea what might be causing this?

[Pierre Ossman]

x0vncserver doesn't use polling these days. Instead it relies on the X
server informing it when parts of the screen changes. There has
unfortunately been bugs with regard to that...

How is this virtual display set up?

Does everything work fine if you use x0vncserver for your real display?

Regards
--
Pierre Ossman Software Development
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A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

[Timo Kaufmann]

Are you sure? `x11vnc -clip 1080x1440+1920+0` reports

```
01/06/2018 16:44:12 X DAMAGE available on display, using it for polling hints.
01/06/2018 16:44:12   To disable this behavior use: '-noxdamage'
01/06/2018 16:44:12
01/06/2018 16:44:12   Most compositing window managers like 'compiz' or 'beryl'
01/06/2018 16:44:12   cause X DAMAGE to fail, and so you may not see any screen
01/06/2018 16:44:12   updates via VNC.  Either disable 'compiz' (recommended) or
01/06/2018 16:44:12   supply the x11vnc '-noxdamage' command line option.
```

and works without this issue. Might be that x11vnc uses polling in addition to XDAMAGE.

If thats the case, is there anything I can do? I doubt that I can realistically reach the relevant intel developers and convice them to ship a fix withing the next couple of months.

[Pierre Ossman]

On 01/06/18 16:48, Timo Kaufmann wrote:
>>
>> x0vncserver doesn't use polling these days. Instead it relies on the X
>> server informing it when parts of the screen changes. There has
>> unfortunately been bugs with regard to that...
>

> Are you sure? `x11vnc -clip 1080x1440+1920+0` reports
>
> ```
> 01/06/2018 16:44:12 X DAMAGE available on display, using it for polling
> hints.
> 01/06/2018 16:44:12 To disable this behavior use: '-noxdamage'
> 01/06/2018 16:44:12
> 01/06/2018 16:44:12 Most compositing window managers like 'compiz' or
> 'beryl'
> 01/06/2018 16:44:12 cause X DAMAGE to fail, and so you may not see any
> screen
> 01/06/2018 16:44:12 updates via VNC. Either disable 'compiz'
> (recommended) or
> 01/06/2018 16:44:12 supply the x11vnc '-noxdamage' command line option.
> ```
>
> and works without this issue. Might be that x11vnc uses polling in addition
> to XDAMAGE.
>

Hmm... Maybe. Or this is some weird corner case.

> If thats the case, is there anything I can do? I doubt that I can
> realistically reach the relevant intel developers and convice them to ship
> a fix withing the next couple of months.
>

Someone would need to debug this and figure out what is happening. Which
means a developer with such an Intel card and some time to look at
things. :/