The ::drag-motion signal is emitted on the drop site when the user
moves the cursor over the widget during a drag. The signal handler
must determine whether the cursor position is in a drop zone or not.
If it is not in a drop zone, it returns FALSE and no further processing
is necessary. Otherwise, the handler returns TRUE. In this case, the
handler is responsible for providing the necessary information for
displaying feedback to the user, by calling gdk_drag_status().
If the decision whether the drop will be accepted or rejected can't be
made based solely on the cursor position and the type of the data, the
handler may inspect the dragged data by calling gtk_drag_get_data() and
defer the gdk_drag_status() call to the "drag-data-received"
handler. Note that you cannot not pass GTK_DEST_DEFAULT_DROP,
GTK_DEST_DEFAULT_MOTION or GTK_DEST_DEFAULT_ALL to gtk_drag_dest_set()
when using the drag-motion signal that way.
Also note that there is no drag-enter signal. The drag receiver has to
keep track of whether he has received any drag-motion signals since the
last "drag-leave" and if not, treat the drag-motion signal as
an "enter" signal. Upon an "enter", the handler will typically highlight
the drop site with gtk_drag_highlight().
The ::drag-motion signal is emitted on the drop site when the user moves the cursor over the widget during a drag. The signal handler must determine whether the cursor position is in a drop zone or not. If it is not in a drop zone, it returns FALSE and no further processing is necessary. Otherwise, the handler returns TRUE. In this case, the handler is responsible for providing the necessary information for displaying feedback to the user, by calling gdk_drag_status(). If the decision whether the drop will be accepted or rejected can't be made based solely on the cursor position and the type of the data, the handler may inspect the dragged data by calling gtk_drag_get_data() and defer the gdk_drag_status() call to the "drag-data-received" handler. Note that you cannot not pass GTK_DEST_DEFAULT_DROP, GTK_DEST_DEFAULT_MOTION or GTK_DEST_DEFAULT_ALL to gtk_drag_dest_set() when using the drag-motion signal that way. Also note that there is no drag-enter signal. The drag receiver has to keep track of whether he has received any drag-motion signals since the last "drag-leave" and if not, treat the drag-motion signal as an "enter" signal. Upon an "enter", the handler will typically highlight the drop site with gtk_drag_highlight().