R help - Nov 2008 - determining plot location in lattice

Hi,

I'm dealing with a lattice plot inserted into a tk widget and would like 
to know when a user has clicked on the plot area of a plot (i.e. inside 
the axes). For example,

library(tkrplot)
library(lattice)
tt <- tktoplevel()
makePlot <- function() print(xyplot(1 ~ 1))
printCoords <- function(x, y) print(c(x, y))
img <- tkrplot(tt, makePlot)
tkbind(img, "<1>", printCoords)
tkpack(img)

I would like to know when a user clicks inside the axes, but don't know 
how to determine where the plot region is. Essentially, this comes down 
to answering the following question: Assuming the entire plot is on a 
unit square, what are the coordinates of the plotting area?

This question is may seem unrelated to tkrplot, but outside of this 
context I may not get answers that work. I have been playing with both 
lattice::trellis.focus and grid::grid.locator to no avail.

Thanks,

--sundar

As far as R is concerned, the plot in tkrplot is being written to a file and
therefore is not interactive.  So functions like grid.locator and trellis.focus
are not going to work.

You need to use the Tk commands to determine where the mouse is and where a
click occurred, then this needs to be converted to the coordinates of the
trellis plot.  There are some examples of the first part in the TeachingDemos
package, eg TkBrush, TkIdentify, TkApprox, and a couple of others (also the
play.sudoku function in the Sudoku package).  These all work with base graphics
rather than trellis/grid so will not help with the 2nd part.  Possibly something
in the grid package can tell you the coordinates of the various viewports (but
you need to save this information before the end of the plotting command because
the information will probably be lost when the plot finishes).

Hope this helps,

--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Sundar Dorai-Raj
> Sent: Friday, November 07, 2008 12:43 PM
> To: r-help at r-project.org
> Subject: [R] determining plot location in lattice
>
> Hi,
>
> I'm dealing with a lattice plot inserted into a tk widget and would
> like
> to know when a user has clicked on the plot area of a plot (i.e. inside
> the axes). For example,
>
> library(tkrplot)
> library(lattice)
> tt <- tktoplevel()
> makePlot <- function() print(xyplot(1 ~ 1))
> printCoords <- function(x, y) print(c(x, y))
> img <- tkrplot(tt, makePlot)
> tkbind(img, "<1>", printCoords)
> tkpack(img)
>
> I would like to know when a user clicks inside the axes, but don't know
> how to determine where the plot region is. Essentially, this comes down
> to answering the following question: Assuming the entire plot is on a
> unit square, what are the coordinates of the plotting area?
>
> This question is may seem unrelated to tkrplot, but outside of this
> context I may not get answers that work. I have been playing with both
> lattice::trellis.focus and grid::grid.locator to no avail.
>
> Thanks,
>
> --sundar
>
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