This 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, HRGN hRgn, BOOL bRedraw );
Handle to the window whose window region is to be set.
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.
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.
Nonzero indicates success.
Zero indicates failure.
To get extended error information, call GetLastError.
When this function is called, 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, do not make further function calls with this region handle.
In particular, do not delete this region handle. The system deletes the region handle when it no longer needed.
If you call SetWindowRgn on a window, you cannot later move or resize the window.
If you do, you are left with lost regions on the screen that never repaint and never go away. To resolve this, call SetWindowRgn(NULL) before calling SetWindowPos, and then call SetWindowRgn again with the new region.
To obtain the window region of a window, call the GetWindowRgn function.
Windows Embedded CE does not accept regions on windows that fit exactly into entire screen or greater dimensions.