How do you retrieve the visible clipping region for a control?

I have a control where I do some on-screen drawing (specifically
ControlPaint.DrawReversibleLine()), however I need to clip the line to the
visible bounds of my control.

Obviously, the client rect is simple enough to retrieve, but what I need to do
is to clip the line segment to only that portion of the control that is
visible, which may _not_ correspond to the client rect if there is some other
application window partially obscuring my control.

In my tests, Control.CreateGraphics().ClipBounds() is returning an 'infinite'
rectangle.

Anyone have any pointers on how to do what I want in .Net?