Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!bloom-beacon!home.csc.ti.COM!Oren
From: Oren@home.csc.ti.COM (LaMott Oren)
Newsgroups: comp.windows.x
Subject: Re: Detecting/Compressing Multiple Exposure Events - how ?
Message-ID: <2798113409-14017620@SI>
Date: 1 Sep 88 13:43:29 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 46


   Date: 31 Aug 88 18:44:11 GMT
   From: sandra@cs.utah.edu  (Sandra J Loosemore)
   Subject: Re: Detecting/Compressing Multiple Exposure Events - how ?
   
   Any clues on how to do this in CLX?  I just tried some experiments with
   using an EVENT-CASE with :timeout 0 and :discard-p t to scan through the
   event queue, discarding all but the first expose event on a window.  But
   returning T from the clause to indicate that the event should be kept
   would also exit from the EVENT-CASE, so you'd never see whether there
   are more expose events in the queue or not.  I tried doing a recursive
   call to EVENT-CASE to look at the remaining events, but that seemed to
   end up throwing out events it shouldn't have.  I'd appreciate seeing a
   bit of code that actually works.
   
   -Sandra Loosemore

Instead of discarding all but the first, discard all but the last.  That
is, when you receive an :exposure event, ignore it if there's another in
the queue using:

(event-case (display :discard-p t :force-output-p t)
  (exposure (window count)
    (unless ;; Ignore all but the last exposure event
      (event-case (window :discard-p nil :peek-p t :timeout 0)
        (exposure ((window event-window))
          (window-equal window event-window)))
      (refresh window)))
  ;; handle other events...
  )

This technique works well for :motion-notify and enter/leave-notify
event compression.

If you really want to discard all but the first exposure event, the
release 3 version of CLX contains a new form, EVENT-COND, which will
give you the control you want.

An easy way to compress exposure events is to ignore all events with a
non-zero count:
(event-case (display :discard-p t :force-output-p t)
  (exposure (window count)
    (when (zerop count) ;; Ignore all but the last exposure event
      (refresh window)))
  ;; handle other events...
  )