Black or gray screen in the viewer

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diezwei
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Black or gray screen in the viewer

Post by diezwei »

Hi there,
we have many VNC installations here and they all have the same configuration. We use version 1.3.2a for server and viewer in the direct connection. All computers have Windows 10 1909.
VNC is installed as a service in the standard configuration. On approx. 3 clients there is only a black or gray screen after a click to accept the connection. Sometimes the connection is lost and reconnected, but no screen appears.
On the problem PC I am testing the new version 1.3.4.2, but the problem is the same.
The computer with the VNC service has two displays.
What can I do to make the screen appear? Is the problem known? I didn't find anything in the release notes or in the forum.
Thanks for the help.

Ralf Reich
WoodyWoody
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Re: Black or gray screen in the viewer

Post by WoodyWoody »

I actually make a post about this in the 1.3.4.2 version.

https://forum.uvnc.com/viewtopic.php?t=37425

Try the dev version it fixed the issue for us:
https://forum.uvnc.com/viewtopic.php?t=37475


I can't wait for the official release.
diezwei
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Re: Black or gray screen in the viewer

Post by diezwei »

Thanks for answer. I test the dev version....
alazif66
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Re: Black or gray screen in the viewer

Post by alazif66 »

On Dev 1.3.5.0 same problem


Laptop has an external monitor connected, if the user clicks an some application (eg. word , chrome etc.) on the externale monitor screen at the moment when connect to UltarVNC server, the connection is black screen, if during the connection he clicks on the laptop screen, everything is ok.
Last edited by alazif66 on 2021-11-24 12:29, edited 1 time in total.
Rudi De Vos
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Re: Black or gray screen in the viewer

Post by Rudi De Vos »

1) First make sure it isn't a network issue.
If you run the viewer on the same pc and connect to localhost, do you also have a black screen.
2) properties server
[v] ddengine uncheck
DDengine require latest video card and drivers. Possible not supported.
Uncheck to test if this is causing it.

If not running as service.
Suppose you start the vncserver in a rdp session and then minimize or close the RDP session, the rdp video buffer is disabled and vnc is cloning it -> black screen.
diezwei
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Re: Black or gray screen in the viewer

Post by diezwei »

My test with verison 1.3.50 was ok, the viewer shows the display.
I wait for the final version to deploy on all clients.
alazif66
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Re: Black or gray screen in the viewer

Post by alazif66 »

Rudi De Vos wrote: 2021-11-25 20:53 1) First make sure it isn't a network issue.
If you run the viewer on the same pc and connect to localhost, do you also have a black screen.
2) properties server
[v] ddengine uncheck
DDengine require latest video card and drivers. Possible not supported.
Uncheck to test if this is causing it.

If not running as service.
Suppose you start the vncserver in a rdp session and then minimize or close the RDP session, the rdp video buffer is disabled and vnc is cloning it -> black screen.
if ddengine is turned off, the connection works fine, however, when switching to the second screen, two screens appear, but you cannot go to the second screen.
Rudi De Vos
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Re: Black or gray screen in the viewer

Post by Rudi De Vos »

Thats by design, sorry
With the ddengine we can capture each screen sepereate, with a blit you always capture the fullscreen.
Blit -> Prim-All
DDengine= Prim-Sec_third-All

ddengine depend on the video driver, possible there exist a newer driver for your video card that support it. ( normal wddm 1.2)
alazif66
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Re: Black or gray screen in the viewer

Post by alazif66 »

Rudi De Vos wrote: 2021-12-02 21:22 Thats by design, sorry
With the ddengine we can capture each screen sepereate, with a blit you always capture the fullscreen.
Blit -> Prim-All
DDengine= Prim-Sec_third-All

ddengine depend on the video driver, possible there exist a newer driver for your video card that support it. ( normal wddm 1.2)


I checked that the problem could be solved if ultravnc moved the cursor to the main screen before the connection time.
Rudi De Vos
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Re: Black or gray screen in the viewer

Post by Rudi De Vos »

What mouse method is used ( viewer options)
let server deal or Track locally
alazif66
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Re: Black or gray screen in the viewer

Post by alazif66 »

Rudi De Vos wrote: 2021-12-08 17:06 What mouse method is used ( viewer options)
let server deal or Track locally
Ok now the first connection black screen and cursor is automatically moved to the main screen, now the second connection is ok

Thanks Rudi
VersusBG
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Re: Black or gray screen in the viewer

Post by VersusBG »

When the connection is over VPN with improperly configured MTU and MSS it also can cause gray screen. To test this you can use Wireshark and inspect the traffic for drop packets because of DF bit. Only for the test you can restrict the PMTU on both client/server which will limit the packet size to 576 bytes by creating the following registry key in windows:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
EnablePMTUDiscovery dword:00000000
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters]
EnablePMTUBHDetect dword:00000000
If the problem is resolved by limiting the MTU size of the packet then reverse it back to normal by enabling both EnablePMTUDiscovery and EnablePMTUBHDetect. Then go and fix your MTU size of the VPN interface and MSS.
Rudi De Vos
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Re: Black or gray screen in the viewer

Post by Rudi De Vos »

Thanks for the hint
diezwei
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Re: Black or gray screen in the viewer

Post by diezwei »

Next Step.
Now I'm testing version 1.3.6.0 on server and viewer. When a user is logged on to their PC. I have a black screen on my viewer. This PC has two displays. If no user is logged in, everything works fine. I can log in to this PC via Viewer and work as usual.
During testing I noticed something else, if another viewer connects to this PC, the connection breaks and nothing works anymore.
I have only noticed this behavior on pcs with two screens. Windows 21H2 is now installed on the machine, previously it was 1909.
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