Hi
Duncan Murdoch wrote:
On Wed, 01 Dec 2004 08:55:27 +1300, Paul Murrell <[EMAIL PROTECTED]> 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?
Yes.
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.
We could aim for a pretty conservative subset to ensure cross-platformedness and still gain a LOT more compared to the current capture-mouse-click-only. Things like Java's KeyEvent could provide some nice templates to follow.
Paul
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.
Yes, definitely harder.
Duncan
-- Dr Paul Murrell Department of Statistics The University of Auckland Private Bag 92019 Auckland New Zealand 64 9 3737599 x85392 [EMAIL PROTECTED] http://www.stat.auckland.ac.nz/~paul/
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