[xmonad] KeyEvent stream manipulation

Daniel dan.in.a.bottle at gmail.com
Thu Sep 23 11:27:25 EDT 2010

For what I want to do I need to have exclusive access to the keyboard
events so that I can rewrite them. I have been experimenting a bit
with this in XMonad, but passive grabs don't work.

The problem with passive grabs is with overlapping events. This is what happens:
* press key A
* grab converts from passive to active
* KeyEvent keyPress A is delivered to XMonad
* B is pressed
* KeyEvent keyPress B gets delivered to XMonad (B is registered as
passive grab as well, but gets delivered, because technically, we're
in an active grab now)
* A is released
* KeyEvent keyRelease A gets delivered to XMonad
* active grab on A reverts to passive (incl some FocusEvents &
KeymapNotify to inform us that B is still held)
* B is released
* KeyEvent keyRelease B gets NOT delivered to XMonad, it's a regular
KeyEvent, no grab is active, and the passive grab on B is not
triggered, because its keyPress event occurred during another
(shadowing) activeGrab. (Actually, if you keep pressing B, after about
a second or so, X realizes that there should be a grab active and
enters the grab. Unfortunately, this is not fast enough when typing.

Just to be clear, this is a problem of passive grabs, not with XMonad.

Because of this behaviour it seems that the only thing that gets me
there within X is a permanent active grab (keyboardGrab). Other
extensions use active grabs, but they only do this for a limited time,
usually after being triggered (eg. CycleRecentWS, Submap, GridHS,

So my questions:
* Is such a permanent active grab a good idea within X? I'm worrying
about problems interacting with other programs who might attempt grabs
or XMonad losing the grab and not knowing about it.
* If this is not a good idea, what should I look into to get this
capability (exclusive access to transform the keyboard event stream,
before it reaches any application).
* Where/who should I ask to get an informed answer if not here?

My end target are X applications, and I expect that there will be a
tight integration with the window manager (likely XMonad). But I'm
willing to look at a variety of points to hook into the event stream.


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