sec : U Re: widget_control from call_external

[andrew cool <andrew.cool(at)dsto.defence.gov.au>]

JD Smith wrote:
> 
> David Fanning wrote:
> >
> > dominic@work.com (dominic@work.com) writes:
> >
> > >   I have a c/c++ programme that is called from within a
> > >   widget hierachy via call_external.
> > >
> > >   As the computations made take fairly long, I want to update
> > >   a status bar with a 'Percentage complete' from the C-routine,
> > >   so the user doesn't get upset and thinks the programme died
> > >   on him/her.
> > >
> > >   How do I go about that???
> >
> > Well, this will be difficult unless your can call your
> > C program in "chunks", or in some other way interrupt
> > it. It might be easier if you just know, in general,
> > how long it takes. Then you can set a "kitchen timer"
> > sort of progress indicator. As long as the cake is
> > baked by the time the timer goes off, no one seems
> > to care. :-)
> >
> > You can see several ways to build such a progress
> > indicator here:
> >
> >    http://www.dfanning.com/tips/show_progress.html
> 
> I would use alarm() to throw a SIGALRM every 1 second, say, then update
> a percent complete counter, based on some innate knowledge of the
> calculation.  To get this to IDL under call_external is more difficult.
> You *could* then just print it to the terminal, ala:
> 
> printf("\r%02d%% complete",percent_complete);
> 
> Make sure to:
> 
> setbuf(stdout,(char *)NULL);
> 
> first, so the updates will appear.
> 
> Of course, RSI would frown on this, but if it gets the job done...
> 
> If you'd like to do it full blown way, with a snazzy graphical update
> slider, you might have to make a full DLM, and use IDL_Execute to force
> the progress update from the C side.  That's a lot of work for a bit of
> eye candy.  But everybody likes candy.
> 
> Good luck,
> 
> JD

How about using the Widget_Stub functionality to pass an event from the
C
routine to a widget?

Under OpenVMS (at least) in IDL_DIR:[External.widstub] there are simple
examples of how to create your own widget type in C, and how to send
events
to it from C. 

Comments in the file Widget_ArrowB.pro say :-

"While this code is VMS-centric, the principles apply across
platforms..."

Just another example of VMS leading the way.

I can't find the above directory or the example files in my Windows IDL
54
however do a Find in the Online Help for Widget Stub and everything you
need is there.

I've used Widget Stub to animate aircraft positions on a draw widget as
the C code fires off an event.

If a C-dunderhead like me can manage that, anyone can... ;-)
 
Andrew

 ---------------------------------------------------------------------
 Andrew D. Cool                                 .->-.
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