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From: jcb@frisbee.Eng.Sun.COM (Jim Becker)
Newsgroups: comp.windows.open-look
Subject: Re: looking ahead in X event queue
Message-ID: <6404@exodus.Eng.Sun.COM>
Date: 22 Jan 91 21:28:53 GMT
References: <ay4wszz@openlook.Unify.Com>
Sender: news@exodus.Eng.Sun.COM
Lines: 59

wolinsky%isys@uunet.UU.NET (Jeff Wolinsky) writes:

    It would be VERY useful if I could look ahead in my event queue with
    the following conditions:

    	(1) If the specific event isn't found, it shouldn't wait.

    	(2) If the event is found, it should be left in its postion
    	    in the queue.

    I know that XCheckIfEvent() satisfies condition 1 but not 2, whereas
    XPeekIfEvent() satisfies 2 but not 1.  Other than pulling every event
    off the queue and XPutBackEvent() when I'm done, any suggestions?


You can look into  the  queue  yourself,  but  this  isn't  supported,
advised or approved by official channels. If you want to look into the
queue  for events, here is an example of how it can be done. Note that
there  are also things one can do to force flushing and such, but this
is the basic example of how to get in there.

This looks for expose events, and returns boolean.

/*
 *	poke down the queue to see if there are more expose events 
 * 	this looks down the display event queue to see if there is 
 *	another event that is of the exposure type. the content of
 *	the queue is not disturbed. somewhat questionable, but there
 *	is no mechanism that doesn't disturb the queue in Xlib.
 */
no_more_expose( display, window )
Display		*display;
Window		window;
{
struct	_XSQEvent	*qevent;
        Window		ewin;
        int		etype;
	short		found	= FALSE;

        for( qevent  = display->head;
	     qevent != NULL && !found;
	     qevent  = qevent->next ) {

		etype	= qevent->event.xany.type;
		ewin	= qevent->event.xany.window;

		found	= ((etype == Expose) ||
			   (etype == GraphicsExpose)) &&
			   (ewin  == window);
	}

        return !found;
}


-Jim
--
--    
	 Jim Becker / jcb%frisbee@sun.com  / Sun Microsystems