This message is sent to a minimized (iconic) window which is about to be dragged by the user but which does not have an icon defined for its class.
When the user drags the icon of a window without a class icon, Windows replaces the icon with a default icon cursor. If the application needs a different cursor to be displayed during dragging, it must return the handle of a monochrome cursor compatible with the display driver's resolution. The application can call the LoadCursor function to load a cursor from the resources in its executable file and to obtain this handle.
wParam
This parameter is not used.
lParam
This parameter is not used.
The return value contains in its low-order word the handle of the cursor which Windows is to display while the user drags the icon. The return value is NULL if Windows is to display the default icon cursor. The default return value is NULL.
LoadCursor