Changing the release target to "dev" because any changes for this issue are likely to go on the default branch. (That is if someone feels like spending their time on the gnuplot graphics interface at all.)

I agree, probably a separate discussion about the future of Qt graphics in Octave.  It would be interesting to know what the principal problems are with using Qt for publication-quality plots so that they could be addressed.  If it is text quality, rather than graphics quality, then the print options that go through Latex are useful.

Given the long term lack of support for gnuplot, it might still be better to think of segregating computation on to headless servers and then performing the final display / plotting on a machine with Qt.  I find that the graphics produced by gnuplot, even when accurate, to be rather ugly and wouldn't choose that solution even without the complication of remote servers.

FWIW:

xvfb-run --help
Usage: xvfb-run [OPTION ...] COMMAND
Run COMMAND (usually an X client) in a virtual X server environment.
Options:
-a        --auto-servernum          try to get a free server number, starting at
                                    --server-num (deprecated, use --auto-display
                                    instead)
-d        --auto-display            use the X server to find a display number
                                    automatically

seems to work for octave's buildbots.

Dmitri.
--

Presumably this can work, since it did in 6.4.  However, someone would need to be motivated to debug the code.  The core developers rarely have the time for gnuplot-related bugs.

Since the error message is quite specific it might be easy to trace and find the problem by issuing

debug_on_error (1)

before executing the problematic code.

Hi,

Consider this snippet:

h = figure;
hbar = bar(rand(10, 3),'FaceColor','flat');
set(hbar,'edgecolor','flat');
refresh(h);

When run under Octave 7.0.90 with the --no-window-system option (which implies the gnuplot backend), one gets:

error: ccol(1): out of bound 0 (dimensions are 0x0)
error: called from
    __gnuplot_draw_axes__ at line 1162 column 34
    __gnuplot_draw_figure__ at line 169 column 17
    __gnuplot_drawnow__ at line 91 column 5
    refresh at line 47 column 3
    glou at line 4 column 1

This error is related to the set(hbar,'edgecolor','flat') command.

And when that command is removed, there is no crash but one gets gnuplot errors and the resulting graphics is incorrect. This second problem disappears when one removes the 'FaceColor', 'flat' graphics properties.

These issues are regressions, since they do not occur with Octave 6.4.0.

I’m aware that the gnuplot backend is deprecated, but it’s the default when --no-window-system is given (and it’s very useful to be able to generate graphics without a display, e.g. when running testsuites on continuous integration platforms as we do for Dynare).