SetWindowRgn

The SetWindowRgn function sets the window region of a window. The window region determines the area within the window where the system permits drawing. The system does not display any portion of a window that lies outside of the window region

int SetWindowRgn(
  HWND hWnd,     // handle to window whose window region is to be set
  HRGN hRgn,     // handle to region
  BOOL bRedraw   // window redraw flag
);
 

Parameters

hWnd

Handle to the window whose window region is to be set.

hRgn

Handle to a region. The function sets the window region of the window to this region.

If hRgn is NULL, the function sets the window region to NULL.

bRedraw

Boolean value that specifies whether the system redraws the window after setting the window region. If bRedraw is TRUE, the system does so; otherwise, it does not.

Typically, you set bRedraw to TRUE if the window is visible.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero.

Windows NT: To get extended error information, call GetLastError.

Remarks

If the bRedraw parameter is TRUE, the system sends the WM_WINDOWPOSCHANGING and WM_WINDOWPOSCHANGED messages to the window.

The coordinates of a window's window region are relative to the upper-left corner of the window, not the client area of the window.

After a successful call to SetWindowRgn, the system owns the region specified by the region handle hRgn. The system does not make a copy of the region. Thus, you should not make any further function calls with this region handle. In particular, do not close this region handle.

To obtain the window region of a window, call the GetWindowRgn function.

QuickInfo

  Windows NT: Requires version 3.51 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in winuser.h.
  Import Library: Use user32.lib.

See Also

Painting and Drawing Overview, Painting and Drawing Functions, GetWindowRgn, WM_WINDOWPOSCHANGING