The TTM_WINDOWFROMPOINT message allows a subclass procedure to cause a ToolTip to display text for a window other than the one beneath the mouse cursor.
TTM_WINDOWFROMPOINT wParam = 0; lParam = (POINT FAR *) lppt;
The return value is the handle to the window that contains the point, or NULL if no window exists at the specified point.
This message is intended to be processed by an application that subclasses a ToolTip. It is not intended to be sent by an application. A ToolTip sends this message to itself before displaying the text for a window. By changing the coordinates of the point specified by lppt, the subclass procedure can cause the ToolTip to display text for a window other than the one beneath the mouse cursor.