the source surface for this drag
the device that controls this drag
the offered content
the actions supported by this drag
the x offset to @device's position where the drag nominally started
the y offset to @device's position where the drag nominally started
a newly created [class@Gdk.Drag] or %NULL on error
Starts a drag and creates a new drag context for it.
This function is called by the drag source. After this call, you probably want to set up the drag icon using the surface returned by [method@Gdk.Drag.get_drag_surface].
This function returns a reference to the [class@Gdk.Drag] object, but GTK keeps its own reference as well, as long as the DND operation is going on.
Note: if @actions include %GDK_ACTION_MOVE, you need to listen for the [signal@Gdk.Drag::dnd-finished] signal and delete the data at the source if [method@Gdk.Drag.get_selected_action] returns %GDK_ACTION_MOVE.