The InvalidateRect function adds a rectangle to the specified window's update region. The update region represents the portion of the window's client area that must be redrawn.
BOOL InvalidateRect(
HWND hWnd, // handle of window with changed update region
CONST RECT *lpRect,
// address of rectangle coordinates
BOOL bErase // erase-background flag
);
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.
The invalidated areas accumulate in the update region until the region is processed when the next WM_PAINT message occurs or until the region is validated by using the ValidateRect or ValidateRgn function.
The system sends a WM_PAINT message to a window whenever its update region is not empty and there are no other messages in the application queue for that window.
If the bErase parameter is TRUE for any part of the update region, the background is erased in the entire region, not just in the given part.
Windows CE: The hWnd parameter cannot be NULL.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Import Library: Use user32.lib.
Painting and Drawing Overview, Painting and Drawing Functions, BeginPaint, InvalidateRgn, RECT, ValidateRect, ValidateRgn, WM_ERASEBKGND, WM_NCPAINT, WM_PAINT