This example gets the dimensions of the window and calls WinInvalidateRect to invalidate the window. The application will be sent a WM_PAINT message with the entire window as the update rectangle.

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

HWND    hwnd;           /* parent window                        */
RECTL  rcl;             /* update region                        */

WinQueryWindowRect(hwnd, &rcl);

WinInvalidateRect(hwnd,   /* window to invalidate    */
    &rcl,                 /* invalid rectangle       */
    FALSE);               /* do not include children */