[Octave-bug-tracker] [bug #59370] Plotting produces wrong output or takes long time, depending on graphics toolkit

[T Knauss]

Follow-up Comment #6, bug #59370 (project octave):

[comment #5 comment #5:]
> ...
> From what you describe, I guess you are accidentally re-using the gnuplot
figure after you changed to a different graphics toolkit.
> 
> Since commands to gnuplot are sent using a pipe, this can be slow,
especially when drawing lots of objects. Also it might take some time for
gnuplot to load when you first use it.
> Plotting the simple line from comment #0 should be fast though.
> 
> Is that consistent with what you observe?

Yes, your guess is correct. When I use "close all" before the next "plot (S)",
the plot is shown immediately and neither a delay nor high CPU usage occur. I
didn't know that closing the figures manually or via command makes a
difference, and I bet that many other people also don't know that. They just
don't notice, because they never change the graphics toolkit.

This shows that there is room for improvements: When switching the graphics
toolkit, all existing figures should be closed by the switching method,
because they cannot be reused with the new toolkit anyway. Not closing the
figures and deleting all handles from the previous toolkit should actually be
treated as a bug in my opinion.

But, even when staying with gnuplot, if the "plot" command is called multiple
times without "close" in between, the plotting method (in gnuplot) should not
cause such a high CPU usage and long delay. It should check whether a reusable
figure exists, and if not, close orphaned figures and handles before creating
a new one. There is no such problem in "qt" and "fltk".

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