ptspointerpos (POINTS)
The pointer position is in window coordinates relative to the bottom-left corner of the hit-tested window, when the drag operation is started.
fsHitTestres (USHORT)
fsHitTestres provides the hit-test result. It contains the value returned from the hit-test process, which determines the window to be associated with this message. For details of the possible values, see WM_HITTEST.
rc (BOOL)
TRUE