title: How do I determine if a window is off-screen?
body: <p>In Windows XP and above, given a window handle (HWND), how can I tell if the window position and size leaves the window irretrievably off screen?  For example, if the title bar is available to the cursor, then the window can be dragged back on screen.  I need to discover if the window is in fact visible or at least available to the user.  I guess I also need to know how to detect and respond to resolution changes and how to deal with multiple monitors.  This seems like a fairly big deal.  I'm using C++ and the regular SDK, so please limit your answers to that platform rather than invoking C# or similar.</p>