This function maps a set of points from a coordinate space relative to one window into a coordinate space relative to another window.

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

HWND       hwndFrom;  /*  Handle of the window from whose coordinates points are to be mapped. */
HWND       hwndTo;    /*  Handle of the window to whose coordinates points are to be mapped. */
PPOINTL    prgptl;    /*  Points to be mapped to the new coordinate system. */
LONG       cwpt;      /*  Number of points to be mapped. */
BOOL       rc;        /*  Success indicator. */

rc = WinMapWindowPoints(hwndFrom, hwndTo,
       prgptl, cwpt);