Xref: utzoo comp.windows.x:14501 comp.windows.news:1591
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!rutgers!bellcore!spectral!sjs
From: sjs@spectral.ctt.bellcore.com (Stan Switzer)
Newsgroups: comp.windows.x,comp.windows.news
Subject: Re: Help with double-click recognition.
Message-ID: <18012@bellcore.bellcore.com>
Date: 23 Oct 89 13:20:23 GMT
References: <603@granite.dec.com> <1922@bacchus.dec.com> <1490@esquire.UUCP>
Sender: news@bellcore.bellcore.com
Reply-To: sjs@bellcore.com (Stan Switzer)
Organization: Bellcore
Lines: 56

Well, frankly, it comes a quite a surprise to me that you can't do
double click detection in X, but is quite easy in NeWS.

Here's a routine to check if a click is, in fact, a double click.
After you have detected a single click, invoke this routine to see if
there is another click.  Since it just checks to see if another click
follows the current one, it can be cascaded to detect triple,
quadruple, etc. clicks.

    /DoubleClickDelay .3 60 div def
    /DoubleClick? { % - -> another click(true) or not(false)
	null blockinputqueue { % fork
	    ParentCanvas setcanvas
	    currentcursorlocation
	    createevent dup begin
		/Name /MouseDragged def
	    end expressinterest
	    createevent dup begin
		/Action /DownTransition def
		/Exclusivity true def
	    end expressinterest
	    createevent dup begin
		/Name /Timer def
	    end dup expressinterest createevent copy dup begin
		/TimeStamp currenttime DoubleClickDelay add def
	    end sendevent
	    unblockinputqueue
	    WaitButIgnoreJiggle
	    /Action get /DownTransition eq % Have we a click?
	} fork waitprocess
    } def
    /JiggleFudge 4 def
    /WaitButIgnoreJiggle {
	{
	    % get events until something more than a
	    % mouse jiggle happens
	    awaitevent
	    true % exit flag
	    1 index /Name get /MouseDragged eq {
		1 index begin XLocation YLocation end
		% stk: origX origY event exflag X Y
		4 index sub abs JiggleFudge le exch
		5 index sub abs JiggleFudge le and
		{ pop false } if % continue (don't exit)
	    } if
	    { exit } if
	    pop
	} loop
    } def

If you wanted to be more clever, you could download a global click
processor that converted all multiple clicks into distinct events for
distribution.  It would probably be a bad idea, though, since it would
make all single clicks just a little bit sluggish.

Stan Switzer  sjs@bellcore.com