Initiates a drag on the source side. The function only needs to be used when the application is starting drags itself, and is not needed when gtk_drag_source_set() is used.
The event is used to retrieve the timestamp that will be used internally to grab the pointer. If event is NULL, then GDK_CURRENT_TIME will be used. However, you should try to pass a real event in all cases, since that can be used to get information about the drag.
Generally there are three cases when you want to start a drag by hand by calling this function:
2. During a motion-notify-event handler, if you want to start a drag when the mouse moves past a certain threshold distance after a button-press. Pass the event that you have in your motion-notify-event handler.
3. During a timeout handler, if you want to start a drag after the mouse button is held down for some time. Try to save the last event that you got from the mouse, using Event.copy, and pass it to this function (remember to free the event with Event.free when you are done). If you really cannot pass a real event, pass NULL instead.
The targets (data formats) in which the source can provide the data
A bitmask of the allowed drag actions for this drag
The button the user clicked to start the drag
The event that triggered the start of the drag, or NULL if none can be obtained.
The initial x coordinate to start dragging from, in the coordinate space of widget. If -1 is passed, the coordinates are retrieved from event or the current pointer position
The initial y coordinate to start dragging from, in the coordinate space of widget. If -1 is passed, the coordinates are retrieved from event or the current pointer position
the context for this drag