This example uses WinLockVisRegions to prevent any window's visible region from changing while a screen operation is executing. WinLockVisRegions is called before the screen operation to lock the visible regions and again after the operation to unlock the regions.

#define INCL_WINWINDOWMGR       /* Window Manager Functions     */
#include <os2.h>

BOOL  fSuccess;         /* success indicator                    */

/* lock visible regions */
fSuccess = WinLockVisRegions(HWND_DESKTOP, TRUE);

/*
 .
 . executing screen operation
 .
 */

/* unlock visible regions */
fSuccess = WinLockVisRegions(HWND_DESKTOP, FALSE);