On Wed, 01 Dec 2004 08:55:27 +1300, Paul Murrell
<p.murrell@auckland.ac.nz> wrote :
This sounds like the general problem of being able to capture keyboard
input on a graphics device (a key-stroke equivalent of dev_locator).
Robert has been keen on this for a while too.
It would presumably be not too difficult to implement something modal
(like dev_locator) - in effect, a dev_eventloop, which blocks the
command line and processes events (both mouse clicks and key strokes) in
a particular graphics window until a prearranged event to quit. Nasty
modal behaviour, but doable and obviously useful in some ways. Any
interest in that?
You mean something like this?
The user sees a function
graphevents <- function(handler, events = c('mousedown', 'mouseup',
'mousemove', 'keydown', 'keyup') , prompt = 'Please do something')
which calls the handler function with a standard set of args
indicating what event just happened and keeps going until the handler
returns some non-NULL value. So locating a single point could be
implemented as
onmousedown <- function(event, button, x, y) {
c(x,y)
}
graphevents(onmousedown, events='mousedown', prompt='Click on the
graph')
and waiting for the user to hit a key could be implemented as
onkeyup <- function(event, key) {
TRUE
}
graphevents(onkeyup, events='keyup', prompt='Hit any key')
If we wanted both, maybe we could have
graphevents( list(onmousedown, onkeyup), c('mousedown', 'keyup'))
That would be fairly easy to implement in the windows() device, but I
have no idea if it would make sense in other interactive devices.
Issues would be defining what sort of values "key" would take, what
events to allow handlers for, what the event handler arg lists would
look like, and so on. A test of whether it was good enough might be
whether locator() could be rewritten in R.
A much nicer solution of course would be asynchronous event handling in
the graphics window (i.e., you don't block the command line), but that
depends on the event loop integration problem being solved and that does
not look like happening soon.