This example shows how an application can incrementally repaint an asynchronous-paint window one area at a time. While a window is invalid (has a non-null update region), WM_PAINT messages are returned by WinGetMsg. The application uses WinQueryUpdateRegion to obtain a region that requires repainting, and WinValidateRegion to validate the region (reset the update region to null).

#define INCL_WINWINDOWMGR
#define INCL_GPIREGIONS
#include <OS2.H>
HRGN hrgnUpdt, sRgnType;
HPS hpsPaint;
HWND hwnd;
/* Window needs paint           */
        case WM_PAINT:

/* assume we stop any asynchronous drawing.  */
/* by posting a message to the asynchronous  */
/* drawing thread.                           */

hrgnUpdt = (HRGN)GpiCreateRegion(hpsPaint,
                           (ULONG)0,
                           (PRECTL)NULL);

sRgnType = (HRGN)WinQueryUpdateRegion(hwnd,
                                hrgnUpdt);

/* if the region is not null and the call is not in error, */
/* validate the region.                                    */

if ((sRgnType != NULL) &&
   (sRgnType != RGN_ERROR)) {
   WinValidateRegion(hwnd, hrgnUpdt, FALSE);
/*
here we would send the update region handle to an
asynchronous drawing thread. We have already validated the
region, so no more WM_PAINT messages will be sent due to this
region.
*/
       } else { GpiDestroyRegion(hpsPaint, hrgnUpdt);}