graphic: 0.835
vnc: 0.809
device: 0.711
other: 0.643
network: 0.621
semantic: 0.564
instruction: 0.393
mistranslation: 0.392
socket: 0.315
boot: 0.311
KVM: 0.190
assembly: 0.150

VNC outputs garbage in zlib mode

TL;DR: When QEMU is launched with VNC as the output and viewed with a client that defaults to zlib VNC encoding, the resulting output tends to accumulate artifacts.

Reproduction:
Launch QEMU (tried with versions 4.2.0 and 4.1.0 on Linux  64bit) with -vnc 0.0.0.0:0
Connect to it with a VNC client that allows you to select encoding, i.e. UltraVNC.
Set encoding to zlib (type 6), 32bit color.
As screen content changes it starts accumulating artifacts. Almost certain to appear if you open-close windows over a pattern.
Does not seem to depend on guest used, but easier to reproduce with a GUI.

Looks like this: https://orbides.org/img/vnc.png

It appears to be a deflate glitch of some sort - all of the bad pixels are generated by length/distance codes. Can't narrow it down any more.

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.


[Expired for QEMU because there has been no activity for 60 days.]