[Octave-bug-tracker] [bug #50417] overplotting contour over imagesc fails (gnuplot)

[Dan Sebald]

Follow-up Comment #2, bug #50417 (project octave):

This looks like something that was never tested upon making some kind of
change to address something specific to the Qt gnuplot terminal.

Here's what Octave generates for gnuplot to process:


plot "-" binary array=101x101 scan=yx origin=(0,0) dx=0.01 dy=0.01 using 1
title "" with image; \
if (GPVAL_TERM eq "qt") unset obj 1;
unset obj 2; \
plot "-" binary format='%float64' record=40 using ($1):($2) title "" with
linespoints linewidth 0.500000 pointtype -1 dashtype solid pointsize 0.666667
lc rgb "#ff0000" \


There is a continuation character ('\') at the end of the plot command, then
some separate gnuplot command conditional which has nothing to do with the
plot command, then a new plot command.  That obviously is wrong.

Here's the code from __gnuplot_draw_axes__.m that generate the offending
lines:


      elseif (is_image_data (i-1))
        if (bg_is_set)
          fputs (plot_stream, "if (GPVAL_TERM eq \"qt\") unset obj 1;\n");
          bg_is_set = false;
        endif
        if (fg_is_set)
          fputs (plot_stream, "unset obj 2; \\\n");
          fg_is_set = false;
        endif
        fprintf (plot_stream,"%s \"-\" binary format='%%float64' %s %s %s
\\\n",
                 plot_cmd, usingclause{i}, titlespec{i}, withclause{i});


The logic here is obviously wrong, given there is no special consideration
just a few lines above that would leave off the continuation character ('\'). 
I will look into this.


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