Path: utzoo!attcan!uunet!wuarchive!rex!uflorida!gatech!bloom-beacon!dont-send-mail-to-path-lines
From: andy@lgc.COM
Newsgroups: comp.windows.x
Subject: Re: Possible Event Handler Bug
Message-ID: <9101122029.AA08824@kiwi.lgc.com>
Date: 12 Jan 91 20:29:27 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 20

uunet!sting.berkeley.edu!scott (Scott Silvey) writes:
> Basically, on a ButtonPress event, I want to start tracking the mouse by
> installing a PointerMotion event handler.  Unfortionately, the PointerMotion
> handler doesn't actually get registered ... annoying as hell.

The problem here is the implicit pointer grab that the server starts when
the pointer button goes down (see 8.4.1.1 of the Scheifler/Gettys/Newman
book).  That grab selects for those pointer events that you were already
selected for when the button went down.  Changes made with XSelectInput
(via XtAddEventHandler) while the button is still down don't take effect
until the button is released, which is not what you want.

I think if you call XChangeActivePointerGrab in your button press
event handler with a mask that includes PointerMotionMask and
ButtonReleaseMask, your problem will go away (but I haven't actually
run the test).

Andy Dysart			(andy@lgc.com)
Landmark Graphics Corp.		Tel: (713) 579-4762
Houston, TX  77094		Fax: (713) 579-4814