NAME
        ViewPortAddress -- Return the address of a window's viewport.

    SYNOPSIS
        viewport = viewportaddress( window )
        D0                          A0

        struct viewport *viewportaddress( struct window * );

    FUNCTION
        Returns the address of the viewport associated with the specified
        window.  The viewport is actually the viewport of the screen within
        which the window is displayed.  If you want to use any of the graphics,
        text, or animation primitives in your window and that primitive
        requires a pointer to a viewport, you can use this call.

        This pointer is only valid as long as your window's screen remains
        open, which is ensured by keeping your window open.

    INPUTS
        window = pointer to the window for which you want the viewport address

    RESULT
        Returns the address of the Intuition viewport structure for
        your window's screen .

    BUGS
        This routine is unnecessary: you can just use the expression
        &Window->WScreen->ViewPort.

    SEE ALSO
        graphics.library