Zoom rectangle code

> Hi,
>
> I,m searching for code to bring up a zoom rectangle in a double buffered
> view. Something like click into a view hold the mouse button and drag to
> another point showing the rectangle from start point to mouse position.
>
> I could do it via MouseTracker but if there is a free code snippet, I
> haven't to rediscover the wheel.
>
> Thanks
> cjb