Tearing / Flickering / Graphical bugs, Nvidia 4060 Ti

[JubilantJerry]

If you'd like to put out an incentive for fixing this bug, you can do so at https://issuehunt.io/r/LibVNC/x11vnc

Describe the bug

On my system (Ubuntu on Xorg 24.04, Nvidia 4060Ti, LAN connection), the screen seen by the VNC client tends to flicker on random subareas of the screen when there are frequent updates on the screen. I'm not sure if this should be called tearing or flashing or some other visual bug.

The contents that flicker in mostly look like random rectangles that are showing bits of the desktop below the window, they are transient and seem to disappear within 0.1 seconds. The flickering occurs throughout the screen in unpredictable locations.

The issue occurs even if the network connection is very fast between the client and the server. I've tried directly connecting to two via Ethernet, the connection itself would be smooth and the client can see videos play without any lag, but the flickering artifacts still will appear very frequently.

To Reproduce

It seems that x11vnc default options cause the flickering, and I haven't found any options that prevent it.
It is much more likely to happen when my Nvidia GPU is in power mode P5 or higher (i.e. when it is relatively idle). It becomes much less pronounced when my Nvidia GPU is under load and uses power mode P2 or lower.
Flickering is significantly reduced if I use -snapfb, if the Nvidia GPU is also in P2 or lower the flickering almost entirely stops.
A possible workaround for others facing the issue will be to use -snapfb and run CUDA kernels every 10 seconds.

Expected Behavior

Screen should not flicker. It's fine if the screen lags, but flickering is visually more disruptive.

Screenshots

Desktop (please complete the following information):

• OS and version: Ubuntu 24.04
• Xorg version used: xorg-server 2:21.1.12-1ubuntu1.1
• Graphics driver: nvidia-driver-550
• VNC viewer: TigerVNC, Remmina

Additional context