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From: swick@athena.mit.EDU (Ralph Swick)
Newsgroups: comp.windows.x
Subject: Re: Xt Intrinsics, extensions, and event handlers
Message-ID: <9105301452.AA24478@lyre.MIT.EDU>
Date: 30 May 91 14:52:49 GMT
References: <1224@mdavcr.UUCP>
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 68


    I would like to know if there is any way of providing Xt Event handlers
    to handle events that come from X extensions.

Unfortunately no, not at the present time.

     The event type of these
    events is not known until the extension is initialized, and the event
    cannot be selected with XSelectInput.

Correct.  This is only one of the difficulties involved in adding
such support.

    The problem is that Xt doesn't seem capable of dispatching any nonmaskable
    events to the event handler other than GraphicsExpose, NoExpose,
    MappingNotify, SelectionClear, SelectionRequest, SelectionNotify, and
    ClientMessage

Also correct.  These are very explicitly specified to be the [only]
events referred to by the 'nonmaskable' argument to XtAddEventHandler.
Actually, MappingNotify is a mistake; see below.

    Shouldn't event types outside the range of the X standard protocol be
    considered nonmaskable events by Xt?

Perhaps but that would now be a significant backwards-incompatible
specification change and is therefore not acceptable.  An additional
difficulty is that it is not correct to assume (or require) that
all extension events have usable 'window' fields.  MappingNotify
is the only core event that doesn't contain a window and it requires
quite a bit of internal manipulation in Xt to dispatch it reasonably.

An aside; rather than "fixing" the implementation to dispatch
MappingNotify to all event handlers registered with nonmaskable==True,
we propose to change the spec to remove this event from the 'nonmaskable'
list.  As of R4, it is possible to express interest in MappingNotify
through the translation table mechanism and this appears adequate.

My own personal belief is that full extension event support in Xt
should allow a widget to register interest in any event, not just
those containing windows.  Extension events should also be supported
both through translation tables and through the more primitive
event handler mechanism.  Getting events dispatched to the right
place is only half the problem; the other half (and the harder
one, it appears to me) is requesting them from the server in the
first place.

    is there any possibility that this
    will change with X11.R5?

I can pretty much guarantee that full extension event support
will not appear in R5, sorry to say.  No guarantees, but some
"experimental" code might be included with the distribution.

    Looking at the sample implementation, it seems that all that would be
    required ...

I hope I've convinced you that this is far from sufficient.

    Steve Furr ( furr@mda.ca )

    Lesser artists borrow,
    great artists steal.

	- blatantly stolen from
	  Igor Stravinsky

and fools reinvent? :-)