>> maybe worth collecting that list on the wiki

What would be helpful is a list of "I use gnuplot, rather than the default OpenGL toolkit, because..."

There are still cases where gnuplot gives better results. My opinion is that we must fix those and give up doing as if we supported gnuplot.

As gnuplot is not actively supported in Octave, I lowered the priority.

The code for legend was largely re-written by Pantxo and it uses Octave's interface to OpenGL to accomplish what it needs to.  The changes were so profound that it was not possible to update the code AND keep support for gnuplot.  See the start of the legend.m code:

function [hleg, hleg_obj, hplot, labels] = legend (varargin)

  ## Use the old legend code to handle gnuplot toolkit
  if (strcmp (graphics_toolkit (), "gnuplot"))
    if (nargout > 0)
      [hleg, hleg_obj, hplot, labels] = __gnuplot_legend__ (varargin{:});
    else
      __gnuplot_legend__ (varargin{:});
    endif
    return;
  endif

The very first thing that is done is to check the graphics toolkit.  If it is gnuplot, we use the old m-file code from previous Octave versions (with all of the problems that it had).  There is no plan to update _gnuplot_legend_ code, although patches against it would probably be reviewed and accepted.

Apologies if this overlaps any of the other gnuplot legend bugs. A search didn't show any that appeared to match. Apologies if this is a missed duplicate.

Following on a question over in StackOverflow [1], there is a plotting bug that only occurs with gnuplot, where the legend is improperly sized depending (seemingly) only on whether the text is uppercase.  it appears to size the legend based on lowercase text. A simple test case:

plot([1 2 3],[4 5 6], 'DisplayName','thisisaverylongname');legend

figure

plot([1 2 3],[4 5 6], 'DisplayName','THISISAVERYLONGNAME');legend

produces the attached image

(file gnuplot_simplelabellengthtest.png)


Note that if a lower case name the same length as the upper case name above has the legend box the correct size. (e.g., "thisisaverylongname1234" takes about the same amount of space on the screen as "THISISAVERYLONGNAME", but the former has a larger legend to accommodate it while the latter does not.

[1] https://stackoverflow.com/questions/64986635/octave-box-legend-not-proper-width-with-upper-case-text