This function subtracts the update region (invalid region) of a window from the clipping region of a presentation space.

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

HPS     hps;          /*  Presentation-space handle whose clipping region is to be updated. */
HWND    hwnd;         /*  Window handle. */
LONG    lComplexity;  /*  Complexity value. */

lComplexity = WinExcludeUpdateRegion(hps,
                hwnd);