Dragging a Canvas::Line with the mouse?

[walt <w41ter gmail com>]

Hi again,

I need to draw a vertical line on a canvas, to be used as a cursor
that can be moved horizontally in response to a mouse click or a
keystroke.

The only graphics trick I know is to draw the line by XOR'ing it
with the canvas and again a second time to erase it.  (That's to
avoid redrawing the whole screen with every move of the cursor.)

Is there a way to do that with gtk-perl?