This function sets the visibility state of a window.

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

HWND    hwnd;            /*  Window handle. */
BOOL    fNewVisibility;  /*  New visibility state. */
BOOL    rc;              /*  Visibility changed indicator. */

rc = WinShowWindow(hwnd, fNewVisibility);