This function validates the client area within a rectangle by removing the rectangle from the update region of the specified window.
BOOL ValidateRect( HWND hWnd, const RECT* lpRect );
Handle to the window whose update region is to be modified.
If this parameter is NULL, the system invalidates and redraws all windows and sends the WM_ERASEBKGND message to the window procedure before the function returns.
Long pointer to a RECT structure that contains the client coordinates of the rectangle to be removed from the update region.
If this parameter is NULL, the entire client area is removed.
Nonzero indicates success.
Zero indicates failure.
To get extended error information, call GetLastError.
Passing in a NULL value for the hWnd parameter is not supported.
The BeginPaint function validates the entire client area.
The ValidateRect function should not be called if a portion of the update region must be validated before the next WM_PAINT message is generated.
The system continues to generate WM_PAINT messages until the current update region is validated.