| Using WIDGET_EVENT to break into loops [message #6714] |
Wed, 07 August 1996 00:00  |
andyhall
Messages: 1
Registered: August 1996
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Junior Member |
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Hi all.
I have been writing an application that uses a loop to
perform animated data visualization, and I wanted to add the
functionality to stop the loop before the animation was
complete. In searching for a good way to do this, I came
accross the following post from this group in answer to a
similar question:
> Check out the !NEWS IDL Newsletter Volume 6, Number 1 (Summer 96)
> if you have it. It has an example illustratiing how to do what you
> are asking.
>
> Basically, within the loop in the event handler, you use
> WIDGET_EVENT() to poll for events generated from the widget
> heirarchy "represented" by the widget id argument to WIDGET_EVENT().
>
> Something like:
>
> quit_loop = 0
> while ( quit_loop eq 0 ) do begin
> ...
> quit = WIDGET_EVENT( event.top, /nowait )
> if ( quit.id eq state.cancel_button ) then $
> quit_loop = 1
> ...
> endwhile
>
> Hope this helps.
> Dave Foster
> foster@bial1.ucsd.edu
For reference, my routine uses a large graphical interface
with an event handler processing all the user input. I use
the xmanager routine to handle the widgets.
So, I tried the advice above. However, I had a few problems:
The above message (and the IDL help) seem to imply that
WIDGET_EVENT(id) is a routine that will extract events for the
hierarchy rooted at id and hand them over to the user to examine.
However, when I call WIDGET_EVENT, the procedure polls the hierarchy
rooted at id for events, then passes those events to the event handler,
processes the event, and _then_ returns the event to me.
Thus, when I implemented the above code, or rather this code:
WHILE NOT(quit_anim) DO BEGIN
...
quit = widget_event(event.top, /nowait)
IF quit.id NE 0 THEN quit_anim = 1
END
However, since the widget_event routine was processing the events
it found, by the time it got to the IF statement, the event struct
was cleared, and quit.id was always zero no matter what.
The only way I could find to break the loop was to add a button to
the same hierarchy such that the button's event exedcuted the command
quit_anim = 1
This breaks the loop, but is not satisfactory for several reasons, chief
among them being that this requires that the application process ALL
events generated in that entire hierarchy during execution of the loop.
Sorry about the involved nature of this post, but I would greatly
appreciate anyone's advice.. I don't know if I should be structuring my
event handling differently, or if I am using widget_event wrong, or what.
Anyway, thanks in advance...
Andy Hall
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| Re: Using WIDGET_EVENT to break into loops [message #6789 is a reply to message #6714] |
Tue, 13 August 1996 00:00  |
Peter Mason
Messages: 145
Registered: June 1996
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Senior Member |
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I'm fraying this thread a little, I know, but I was wondering if anyone
else has blocked-event problems in IDL 4.0.1 under Windows NT (3.51).
I use the WIDGET_EVENT(stop_button,/nowait) technique to allow users to
break out a processing loop, and it works fine under Unix.
However, it only works sometimes under NT - it seems that if my loop is not
complicated enough then IDL totally hogs the CPU and mouse clicks don't get
through at all. The WAIT() function does provide an escape, but it slows
things down considerably (even with the smallest usable delay) and flickers
the main window's title annoyingly. Setting input focus to the button just
before the loop will allow the user to break out by pressing the spacebar
(this gets through), but you can't expect a user to guess that (s)he has to
do this instead of clicking the mouse.
Has anyone found a way around this, or is it an NT setup thing specific
to my machine?
Peter Mason
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