This function finds the window below a specified point, that is a descendant of a specified window.

#define INCL_WINWINDOWMGR /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HWND       hwndParent;     /*  Window handle whose child windows are to be tested. */
PPOINTL    pptlPoint;      /*  The point to be tested. */
BOOL       fEnumChildren;  /*  Test control. */
HWND       hwndFound;      /*  Window handle beneath pptlPoint. */

hwndFound = WinWindowFromPoint(hwndParent,
              pptlPoint, fEnumChildren);