| Re: Interrupting widget applications [message #7912] |
Sun, 26 January 1997 00:00  |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Sam Haimov <haimov@uwyo.edu> quotes M. Hegde with respect to interrupting loops
in widget programs:
>> So far the most convenient method I have found out is to monitor the event
>> queue with WIDGET_EVENT( interrupt button ) wherever the interrupt is desired
>> and proceed accordingly.
He goes on to write:
> I have similar experience.
>
> My application uses widgets for a real-time radar display. It can show
several different
> images on one or two windows and includes various widget controled
features. The main
> reason I am using widget_event to handle widgets is the fact that my main
loop is controled
> by the radar data acquisition system (non-IDL program) and I want the
interrupts to be
> based on the DAQ behaviour rather than on time intervals by TIMER.
Here, in my opinion, is just about the *only* justification for using
WIDGET_EVENT to manage IDL events rather than XMANAGER. Sam is
exactly right. If the locus of control is in an external program, then
I think you want to use WIDGET_EVENT to get IDL widget events
and process them appropriately.
But suppose the locus of control was the IDL widget program.
How could you get the program to respond to real-time events
that were being monitored by an external program?
One possible solution would be to use TIMER events. I typically
set timers on widgets that don't ordinarily receive events.
Usually I use a sub-base, whose only other purpose is to
organize my widget layout. I attach an event handler
to that base to handle the timer event. It looks like this:
subbase = WIDGET_BASE(tlb, EVENT_PRO='Timer_Event', COLUMN=2)
When I am ready to check my external program, I want to get
into the TIMER_EVENT event handler, so I set the timer to
go off immediately, like this:
WIDGET_EVENT, subbase, TIMER=0.0
Now I am inside my TIMER_EVENT event handler. Here I can do
whatever it is I need to do. For example, I can check my external
program to see if any new data has come in from my instruments.
If it has, I can plot it.
When I am finished doing whatever it is I need to do, I am set
to exit my event handler. If I want to come back periodically
I need to set the next timer event before I exit. Suppose I wanted
to check for new data every 1.5 seconds, then I would probably
have code like this at the bottom of my TIMER_EVENT event
handler:
IF info.stop NE 1 THEN WIDGET_CONTROL, event.id, TIMER=1.5
The info.stop variable is a stop flag that is usually set by a
STOP or INTERRRUPT or CANCEL button of some sort. In 1.5
seconds, I get back into this event handler for the next
round of doing whatever it is I do. But meanwhile, I can be
processing whatever other events are being generated by
my widget program, in the order in which they are being
generated. This will include EXIT buttons, READ DATA
buttons, etc.
If you want to see a good example of a TIMER event in
action, look at the program XMOVIE on my web page.
This program shows you how to do an animation
correctly in a widget program. It is possible to
interrupt the animation because the STOP and START
buttons just cue up the TIMER events.
Hope this gives people some ideas.
David
-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
2642 Bradbury Court, Fort Collins, CO 80521
Phone: 970-221-0438 Fax: 970-221-4762
E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com
-----------------------------------------------------------
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