This example uses WinIsWindowShowing to check if any part of the window is physically visible before causing a redraw of the window via WinInvalidateRect.

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

HWND    hwnd;                 /* Window handle            */
RECTL  rcl;                   /* Update region            */

/* If any part of the window is visible, cause a redraw */
if (WinIsWindowShowing(hwnd))
  {
    WinQueryUpdateRect(hwnd, &rcl);
    WinInvalidateRect(hwnd,   /* Window to invalidate     */
                      &rcl,  /* Invalid rectangle         */
                      FALSE); /* Do not include children  */
  }