Black or gray screen in the viewer

[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]

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]

Thanks for answer. I test the dev version....

[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.

[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]

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]

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]

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]

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]

What mouse method is used ( viewer options)
let server deal or Track locally

[alazif66]

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]

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]

Thanks for the hint

[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.

[SkyBeam]

Interestingly I just had a similar effect.
Had to connect to a Laptop with Windows 10 1909 installed and could see only a black screen. Interestingly the screen appeared for a split second when connecting just before disappearing. Also clicking the screen switch icon caused the screen to show up briefly occasionally.
Granted also the GPU driver is pretty old. It runs on an NVidia Quadro K2000M with drivers from 30. September 2019 (via Windows Update) version 426.25. Actually the official driver provided by nVidia is even older.

However the driver itself seems not to be the main problem. I did also install TeamViewer and it worked perfectly fine to capture the screen. Even more interestingly TeamViewer worked fine but as soon as I connected using UVNC the screen went black on both, UVNC and TeamViewer.

Also I found that the screen is not just entirely black. Opening up the start menu by clicking in the black void around the start menu makes the start menu and task bar appear. But none of the other screen content. No matter what applications are open.

Then I tried to disable ddengine. But it did not change anything. Still black screen.

Next step was a upgrade/downgrade. Upgrading to latest 1.3.7.1 version did not change anything. Version 1.3.6 did show the same issue. But using 1.3.4.2 did work perfectly fine (still using latest UVNC 1.3.7 dev-1 viewer though.

Now it's getting interesting. After I was able to upgrade Windows 10 to build 21H2 it's working just fine with all versions, including 1.3.6 and 1.3.7-dev1.
The display driver however did not change, it's still nVidia 426.25.

[diezwei]

Now I tested with version 1.2.5.0, same behavior.
This PC has an mv video hook driver2 installed and an Intel HD Graphics 630. Next try without the hook driver.
This driver comes from previous installations.

[esus]

Hi,

I also have some issues with black screens. I have 1.3.6.0 installed on Windows Server 2019 Standard with one monitor only.

• when I activate the red frame option on the server, the red frame is visible on the computer where it is installed, but on the viewer I only see a black screen. When I hit the ctrl + alt + del button I can see the screen for 1 second or so and then it goes black again

• disabled red frame, connected to the server, but when I start a RDP connection from this server to my virtual machine or connect with hyper-v connect option to the vm i also get the black screen.

I also installed 1.3.7.1 dev, same problems.
With 1.2.4.0 all works fine. But without the nice features of the new version

[Rudi De Vos]

Cause:

The border use the option WDA_EXCLUDEFROMCAPTURE.
Show the border remote but don't show it on the viewer ( exclude from capture)

Starting in Windows 10 Version 2004, WDA_EXCLUDEFROMCAPTURE is a supported value. Setting the display affinity to WDA_EXCLUDEFROMCAPTURE on previous version of Windows will behave as if WDA_MONITOR is applied.

WDA_MONITOR show it remote and local.

The only thing that's possible is to try to detect the OS version and disable the not supported options.

[SkyBeam]

The only thing that's possible is to try to detect the OS version and disable the not supported options.

This sounds like a good idea. Or perhaps more generically check if the feature is supported and display the frame only if it is properly supported by the OS. Actually I would also not mind seeing the frame in remote VNC display if the OS does not allow to hide it in remote view. So on old systems I would see the frame also in my VNC viewer while on newer systems the frame is only displayed locally.

[Rudi De Vos]

viewtopic.php?t=37538