Getting the panel location of a xyplot matrix using a mouse click in a GDCanvas

Hi:

I would like to find out the panel of a xyplot matrix where a mouse clicked.

I know this functionality is already bundled in trellis.focus but I can't
use it because I am coding a stand alone application in Java using with
GDCanvas as a graphics device.

I tried calling trellis.focus from Java with:
  re.eval("t = trellis.focus()"));
However it did not work for an embedded GDCanvas. The above call to the
trellis.focus() returns null no matter where I click.

(Side note: the functionality must be implemented in the GDCanvas because
trellis.focus does work correctly in JGR)

I wish to handle all the user GUI events in Java to evaluate different
commands in an Rengine.
With a GDCanvas, it's straightforward to get the x y position of a mouse
click with the standard e.getX() and e.getY()
So my handler would look like:
   public void mouseClicked(MouseEvent e) {
       System.out.println("Clicked" + e.getX() + " " + e.getY());
       System.out.println(re.eval("t = trellis.focus()"));
       System.out.println(re.eval("t"));
      // I would update the panel here ...
   }

I am only using Java because:
- I am proficient in Java GUI programmer
- It is multiplatform

Another way of posing the question is:
Given the coordinates from grid.location how can I find out the plane of an
xyplot matrix where the user clicked.

I have tried to figure out how to do it from code using trellis.clickFocus,
but I have have only been playing with R for a week, so I am quite lost
reading R code.