/*
The answer to this one depends upon whether you wish to determine 
if the user can see your whole window, part of your window, or a 
specific point on your window.

The last case is the simplest one: to determine if the user can 
see a specific point, you determine the screen coordinates of that
point, call WindowFromPoint, and check to see if the handle 
returned from WindowFromPoint is the same as yours. If so, the 
user can see that point because its at the top of the Z Order.
*/

BOOL IsWindowCentreVisibleToUser (HWND hWnd)
{
   BOOL  bRetVal = FALSE;
   RECT  rcWnd;
   POINT pt;

   if (IsWindow (hWnd))
   {
      GetWindowRect (hWnd, &rcWnd);
      pt.x = rcWnd.left + (rcWnd.right - rcWnd.left)/2;
      pt.y = rcWnd.top + (rcWnd.bottom - rcWnd.top)/2;

      bRetVal = (WindowFromPoint (pt) == hWnd);
   }
   return bRetVal;
}


/*
BUT - the down side of this simplistic solution is that 
WindowFromPoint doesn't return handles for disabled windows. 
Ack... so we need something better. Read on...
*/


/*
Things get a little more complicated if we're talking about all 
or part of a window. Basically, the trick is to make the system do
the work for you by using the clipping system. Take a look at the 
code below.
*/

#define IWVTU_FULL     1
#define IWVTU_PARTIAL  2
#define IWVTU_HIDDEN   3
#define IWVTU_ERROR    4


UINT IsWindowVisibleToUser (HWND hWnd)
{
   UINT uRetVal = IWVTU_ERROR;
   int  iClipRes;
   HDC  hdcWnd;
   RECT rcWndClient;
   RECT rcWndClip;

   if (IsWindow (hWnd))
   {
      hdcWnd = GetDC (hWnd);
      GetClientRect (hWnd, &rcWndClient);
      iClipRes = GetClipBox (hdcWnd, &rcWndClip);
      ReleaseDC (hWnd, hdcWnd);

      switch (iClipRes)
      {
         case NULLREGION:
              uRetVal = IWVTU_HIDDEN;
              break;

         case SIMPLEREGION:
              if (EqualRect (&rcWndClip, &rcWndClient))
                 uRetVal = IWVTU_FULL;
              else
                 uRetVal = IWVTU_PARTIAL;
              break;

         case COMPLEXREGION:
              uRetVal = IWVTU_PARTIAL;
              break;

         default:
              uRetVal = IWVTU_ERROR;
              break;
      }
   }
   return uRetVal;
}