[Pkg-octave-devel] Bug#675509: still problems with Emacs inferior-octave mode iwth 3.8.0

[Mike Miller]

On Fri, Mar 07, 2014 at 19:44:30 +0100, Francesco Potortì wrote:
> Good news first:
> 
> launching Octave 3.8 from screen under a virtual terminal shows no
> problems with fltk.  Same from the gui.
> 
> From inside the inferior-octave emacs mode, the plot window appears and
> is regularly updated if I make a new plot.  If it is resized, the plot
> inside is resized only if I replot it.  It freezes if I use close or use
> the mouse to close the window.

Ciao Francesco,

More good news. In case you're not monitoring the upstream bug, I
commented that I am now able to reproduce this and think I know the
cause.

The fltk toolkit relies on the readline event loop running in the Octave
shell as its event loop. If readline is disabled (--no-line-editing) or
was not compiled in Octave (not the case for Debian) then fltk exhibits
exactly the behavior you are describing. It is responsive to commands
from the interpreter but freezes after that and cannot react to events
originating from the windowing environment.

When Octave is running in the Emacs inferior mode, it is given the
--no-line-editing option. Therefore, I believe that this is the same
underlying cause. And that means that fltk cannot work within Emacs
currently.

I think there are two possible ways forward. This can be discussed with
the Emacs maintainers to see if that option can be removed. If Octave
does run readline, does it fatally break the inferior mode interface to
Emacs, or is it just doing extra work and the mode authors thought they
would be saving some overhead?

Another way is to simply prevent the fltk toolkit from being selected as
the active toolkit when readline is disabled in Octave. This is already
done when DISPLAY is unset, for example. Gnuplot would be used as a
fallback.

Of course, if you or anyone else can show a case where this fltk problem
still happens without the --no-line-editing option and outside of Emacs
mode, then there may still be an undiagnosed problem with fltk.

-- 
mike