Graphics corruption artifacts issues

[knro]

I installed x11vnc from Github on Ubuntu Server 18.04 for RPI3B+ on armhf architecture. It is managed by a systemd service:

[Unit]
Description=Start x11vnc at startup.
Before=novnc.service
After=multi-user.target
 
[Service]
Type=simple
ExecStart=/usr/bin/x11vnc -avahi -forever -shared -rfbauth /home/knro/.vnc/passwd -autoport 5900 -auth /var/run/lightdm/root/:0
Restart=on-failure
RestartSec=2

[Install]
WantedBy=multi-user.target

When I try to connect to it either directly via using VNC clients like KRDC, TigerVNC..etc, then I get severe graphical corruption. It seems mostly to affect Qt applications (this is running on Ubuntu Mate with lightdm) though the artifacts also affect to lesser degree GTK applications. The corruption also shows on noVNC.

What's odd is that there is no corruption when using RealVNC. Attach is a screenshot for my 3-monitors using from left to right (KRDC --> RealVNC --> TigerVNC). You can see the corruption on the first and third monitors. I tried to play with many x11vnc settings to no avail. The same artifacts also appear when using the x11vnc from the official 18.04 repo.

[bk138]

You might try playing around with the different methods of getting the framebuffer in x11vnc. -snapfb or sth around -noxdamage come to mind. There are a lot of them :-)

[knro]

I tried almost all the combination to no avail :-(

I don't know why this bug showed up in 18.04. But it doesn't matter if I use the Ubuntu x11vnc or Github version, they both experience the same graphics corruption.

[bk138]

@knro Can you try with an older x11vnc version and maybe find a last-good one?

[bk138]

@knro which LibVNCServer version are you using?

[bk138]

@username729 Does the issue show with Raspbian Jessie as well?

[username7291]

No it works perfect with Jessie. The intresting is on Jessie i too updated the Firmware to the new Version and it still works. Means its a Problem in the Operating system or related to drivers that
are only in use with 3B+/4B Hardware.
If i could i would still use Jessie but the minimum Requirement for RPI4 ist Buster and for RPI3B+ its stretch in the later Versions.

[bk138]

Let's try a theory: X.org version and/or drivers used. What are the differences? Did they maybe add a new acceleration method?

[username7291]

Im have not much knowledge about the working of Linux graphics system.
The PI4 has 2 HDMI ports and 3D support its VideoCore VI
(OpenGL-ES 3.0; 4K) instead of VideoCore IV (OpenGL-ES 1.1/2.0; Full HD 1080p30) . The 3D i disabled already without luck.
The PI3B+ is almost the same like PI3 but they attached the wifi not via usb but via spi and add a new gigabit ethernet->usb chip, cause of this i think the requirement is stretch.
I tryed downgrade lightdm to 1.10.3-3 and installed xorg(seems not installed before) both doesnt help. I would guess they indroduce some type of Bug in the Operating System layer.

[bk138]

You might want to try the new GL driver: https://github.com/raspberrypi/documentation/blob/master/configuration/raspi-config.md#gl-driver

[username7291]

I tryed with no luck:
-1 Legacy+2 GL (Fake KMS) (no other options)
-Disable 4K&Composite
-enable/disable xcompmgr
-set screenmode again
-disable pixel doubling

[username7291]

-fixscreen V=0.1 helps a little bit while typing. You can almost read what you type into the shell with this.
But like a full refresh request it doesnt fix all all errors on the screen, even not the unchanged screen parts.
Too i tryed alot of other options like snapfb,noxdamage,xwarppointer,xinerama, xd_area, nowcr.
Im updated mesa to the newest and i downgraded mesa to 18.3.6-2.
I tryed too downgrading xserver-org-core to 2.1.16.4 but this dont boot to gui.

[username7291]

It seems like this only happend if tight encoding is set, not on: RAW,Hextile,RRE,ZRLE
Maybe related to LibVNC/libvncserver#363
krfb use the libvncserver and has the identical Problem.