Re: Removing __init_qt__ dependency on libgui

[John W. Eaton]

On 11/17/20 5:27 AM, Alex Leach wrote:
> *From:* John W. Eaton <jwe@octave.org>

>     As you note, however, the Qt graphics code is not usable
>     without the Octave interpreter.  So why not have your application start
>     the interpreter and interact with it to create plots using the Qt
>     graphics code?
>
> This was exactly what I had originally been attempting, however I was 
> really struggling to get it to work. My 'simple' example got larger and 
> larger as I was implementing various derived classes (e.g. octave_link) 
> in attempts to get figures to show with the qt backend, using the 5.2.0 
> release code. I finally got the figures to show, but none of the toolbar 
> or menubar buttons worked. I then noticed the really small example file 
> in the original QtHandles github repository (that I linked to in my 
> previous email) and realised a small example might not need to be any 
> more complicated than that. However, over the last year or two, 
> dependencies on the main GUI have crept in to the qthandles code, so 
> that when I ran the example (replacing octave_main with 
> octave::cli_application, then executing that), loading __init_qt__ 
> results in missing symbol errors from liboctgui. Linking against 
> liboctgui would fix these issues, but I think should be unnecessary.

OK.  My goals for the Qt graphics code in Octave was focused mostly on 
getting it to work better in the context of the Octave GUI and I wanted 
to eliminate the global access to the interpreter and GUI objects.

But before we go too far discussing details, I'd like to agree on the 
goals.  How do you want to use the Octave graphics code?  I imagine that

  octave::interpreter octave_interpreter (...);
  QOctaveGraphics *graphics_widget
    = new QOctaveGraphics (parent_qt_widget, octave_interpreter);

where you create the graphics widget that is linked to your already 
initialized embedded Octave interpreter or perhaps

  QOctaveGraphics *graphics_widget
    = new QOctaveGraphics (parent_qt_widget);

and the QOctaveGraphics widget will initialize it's own interpreter 
object would be reasonable.  However, due to global variable usage in 
the interpreter, only one Octave interpreter is allowed in a given 
process so only one graphics object could be created this way.

Is that the kind of thing you would like to do?  If so, how would you 
interact with this object?  Would you use interpreter functions to 
create plots or would you use Qt signals to pass data and plot options 
to the graphics widget?

jwe