Path: utzoo!attcan!uunet!husc6!bloom-beacon!WSL.DEC.COM!haynes
From: haynes@WSL.DEC.COM
Newsgroups: comp.windows.x
Subject: Re: X Toolkit and continuous graphic output
Message-ID: <8807251653.AA22284@gilroy.pa.dec.com>
Date: 25 Jul 88 16:53:32 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 41


	Suppose I have a program that continuously computes and generates
	graphic output; how can I wrap the toolkit around this program?  It
	seems to me that once I call XtMainLoop() I've given up control and
	there's no way for me to get to the main routine of my program that
	generates the output.

As usual with the toolkit there are at least four equally valid ways of
solving your problem, depending on your exact requirements. They are:

	Work Procs
	Timer Events
	Custom XtMainLoop
	"Pull" instead of "Push"

The Work Proc solution would be to divide your program into small
pieces, each of which would be expected to finish in a small amount of
time (say 100 millisecs) and register each piece as a work proc. If
your graphics program can be decomposed into a 100 millisec task that
is run over and over, this would be your best solution.

Timer Events are a way of getting the toolkit to "wake up" every so
often and call some procedure of yours. This solution is almost always
inferior to work procs, but if you already have some work procs and
want to guarantee that your program runs every n milliseconds, this is
the route to take.

A Custom XtMainLoop is another possibility. Write your own XtMainLoop
with your graphics processing interspersed between the calls to
XtNextEvent and XtDispatchEvent. Further, you can avoid blocking by use
of XtPending.

The last alternative "pull" instead of "push" is actually an
elaboration of the custom XtMainLoop. Take your existing graphics
program and sprinkle "XtNextEvent" followed by "XtDispatchEvent" in
appropriate places. You can even look at the event delivered by
XtNextEvent to decide exactly what it is you want to do.

Good luck.

	-- Charles