RedrawWindow(Handle hWnd Pointer lpRcUpdate Handle hrgnUpdate Integer flags)
updates the specified rectangle or region in a window's client area.
Handle to the window to be redrawn
Pointer to a RECT structure containing the coordinates of the update rectangle. Ignored if the hrgnUpdate parameter identifies a region.
Handle to the update region. If both the hrgnUpdate and lprcUpdate parameters are NULL, the entire client area is added to the update region.
Specifies one or more redraw flags.
If the function succeeds, the return value is nonzero. If the Function fails, the return value is zero.