Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!sun!frisbee!jcb
From: jcb@frisbee.Sun.COM (Jim Becker)
Newsgroups: comp.windows.x
Subject: Re: Browsing Event Queue
Message-ID: <142429@sun.Eng.Sun.COM>
Date: 13 Sep 90 22:07:00 GMT
References: <9009121836.AA16685@ATHENA.MIT.EDU>
Sender: news@sun.Eng.Sun.COM
Lines: 82

Jean-Christophe.Dhellemmes@MAPS.CS.CMU.EDU writes:


   I would like to be able to browse through the entire event queue in my
   refresh loop and interrupt the refresh loop if an expose or resize event is
   in the queue.

   - Is there an official way to do what I need (like getting a pointer to the
   event queue) ? 

I've  had  need  to  do  the same sort of thing. Wanted to avoid doing
exposure  processing if there are more exposure events in the incoming
queue. Didn't  find  anything  efficient  and  suitable  in  the  Xlib
grabbag.

   - Is there another method ?

Yes,  look  at  the  events that hang off the display event list. Note
that  this isn't really legal, but I haven't yet had problems with it.
The same sort of code within the Xlib itself does calls  to  lock  and
unlock the display, but on Suns (last time I checked) they were noops.

Here is some code that can be used to scan the list:

/*
 *	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;
}


in the event processing I do this sort of logic:

	switch( xevent.type ) {

	...

	case Expose:
		/* only do the last one in the queue */
		if( no_more_expose( display, xevent.xany.window ) )
			repaint_window( args );
		break;

	...

	}


It's not directly legal, but filled a void I found in  my  needs.  One
can  get  more  exotic  additionally, in that flushing and event queue
reading  can  be  added  to  the  scan  logic.  (This is used for best
assurance  that  there  is  nothing  pending on the wire.) The example
posted is the simple case.

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