plots are blank with qt and fltk toolkits

[David Lawrence]

Sometimes my desktop session gets into a state where octave plots are blank when using qt and fltk toolkits. The gnuplot toolkit works but isn't maintained and has known limitations. This may be a problem with my desktop session/graphics state, but octave is the only app that I notice a problem with, so I'm reporting the problem against octave for now.

I think I found a report of the same/similar problem:
https://stackoverflow.com/questions/46530224/plot-generated-in-octave-is-fully-black

But there was no solution other than to use gnuplot.

Usually if I reboot or logout and log back in, the problem goes away. Plots in octave sessions that existed before the problem started continue to work. And new plots can be created from those pre-existing octave sessions that look fine. It's only a problem with octave sessions started after a certain point in time and then all new octave sessions are unable to plot without the gnuplot toolkit.

I am in Ubuntu 22.04 now, but I saw it in 20.04 as well.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: octave 6.4.0-2
ProcVersionSignature: Ubuntu 5.15.0-43.46-generic 5.15.39
Uname: Linux 5.15.0-43-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu82.1
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: KDE
Date: Fri Aug 12 11:26:34 2022
EcryptfsInUse: Yes
InstallationDate: Installed on 2022-04-28 (106 days ago)
InstallationMedia: Ubuntu 22.04 LTS "Jammy Jellyfish" - Release amd64 (20220419)
RebootRequiredPkgs: Error: path contained symlinks.
SourcePackage: octave
UpgradeStatus: No upgrade log present (probably fresh install)

[Carl Grundstrom (cgrundstrom)]

I'm running into the same bug. Functions like plot() and scatter() pull up a blank window. I've tried the "fltk" and "qt" graphics toolkits. I've also tried "LIBGL_ALWAYS_SOFTWARE=1 octave". This bug happens with the octave 6.4.0 that is distributed with Ubuntu 22.04, and also with octave 8.1.0 built from source.

The "gnuplot" graphics toolkit fails with an error, so this is not a work around for me:

     gnuplot> set terminal x11 enhanced title "Figure 1" size 560,420 position 300,1540
                      ^
               line 0: unknown or ambiguous terminal type; type just 'set terminal' for a list

     octave:3> WARNING: Plotting with an 'unknown' terminal.
     No output will be generated. Please select a terminal with 'set terminal'.

Also, the use of gnuplot in Octave is deprecated, so it's not a great workaround

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.