Re: widget_control from call_external

[JD Smith <jdsmith(at)astro.cornell.edu>]

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