CWnd::Invalidate

void Invalidate(
   BOOL bErase = TRUE 
);

Specifies whether the background within the update region is to be erased.

The client area is marked for painting when the next WM_PAINT message occurs. The region can also be validated before a WM_PAINTmessage occurs by the ValidateRect or ValidateRgn member function.

The bErase parameter specifies whether the background within the update area is to be erased when the update region is processed. If bEraseis TRUE, the background is erased when the BeginPaint member function is called; if bErase is FALSE, the background remains unchanged. If bErase is TRUE for any part of the update region, the background in the entire region, not just in the given part, is erased.

Invalidate(FALSE)  ->  WM_PAINT

Invalidate(TRUE)   ->  WM_ERASEBKGND   -> WM_PAINT