View source for WinQueryUpdateRegion

This call ''obtains an update region of a window''.

==Syntax==
 WinQueryUpdateRegion(hwnd, hrgn)

==Parameters==
;hwnd ([[HWND]]) - Input: Handle of the window whose update region is to be queried.
;hrgn ([[HRGN]]) - Input: Handle of the region where the window's update region (in window coordinates) will be copied.

==Returns==
;lComplexity (LONG) - returns :Complexity of resulting region/error indicator.
:;RGN_NULL
::Null region.
:;RGN_RECT
::Rectangular region.
:;RGN_COMPLEX
::Complex region.
:;RGN_ERROR
::Error.

==Remarks==
This function is useful for implementing an alternate update scheme to those used by [[WinBeginPaint]] and [[WinEndPaint]], in conjunction with the [[WinValidateRegion]] function.

The application can use the returned update region as the clip region for a presentation space, so that drawing output can be clipped to the window's update region.

==Errors==
Possible returns from [[WinGetLastError]]:
:* PMERR_INVALID_HWND (0x1001) - An invalid window handle was specified.
:* PMERR_HRGN_BUSY (0x2034) - An internal region busy error occurred due to concurrent access from different threads.

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

HWND    hwnd;         /*  Handle of window whose update region is to be queried. */
HRGN    hrgn;         /*  Handle of the window's update region. */
LONG    lComplexity;  /*  Complexity of resulting region/error indicator. */

lComplexity = WinQueryUpdateRegion(hwnd, hrgn);
</PRE>
This example gets the region that needs to be updated and then repaints the invalid region, if necessary.
<Pre>
#define INCL_WINWINDOWMGR
#define INCL_GPIREGIONS
#include <OS2.H>

HWND hwnd;
HRGN hrgn; /* region handle. */

if (RGN_NULL != WinQueryUpdateRegion(hwnd, hrgn)) {
           /* repaint the invalid region  */
                .
                .
                .

}

</Pre>
This example retrieves the update region of a window and repaints it if necessary.

==Related Functions==
* [[WinBeginPaint]]
* [[WinEnableWindowUpdate]]
* [[WinEndPaint]]
* [[WinExcludeUpdateRegion]]
* [[WinGetClipPS]]
* [[WinGetPS]]
* [[WinGetScreenPS]]
* [[WinInvalidateRect]]
* [[WinInvalidateRegion]]
* [[WinIsWindowShowing]]
* [[WinIsWindowVisible]]
* [[WinLockVisRegions]]
* [[WinOpenWindowDC]]
* [[WinQueryUpdateRect]]
* [[WinRealizePalette]]
* [[WinReleasePS]]
* [[WinShowWindow]]
* [[WinUpdateWindow]]
* [[WinValidateRect]]
* [[WinValidateRegion]]
[[Category:Win]]