Redraw entire FXCanvas instead of just exposed parts?

Hi all

I am drawing some text on the screen, which is changed every 3 seconds.
I need to get the canvas to change when the text does. If I move a
window over the text on the canvas, it redraws the exposed parts with
the new text, but I need a way to automatically refresh the whole canvas
when the text is updated. Is this possible? I have searched on
http://www.fxruby.org/doc/api/ and tried refresh, repaint and
forceRepaint which are mentioned there but none of these seem to work.