6. Starting a Drag or Drop

When an initiator starts a drag - or even only a drop -, then it first creates a new property on the source window. The name of this property can be arbitrary, but it must be of type _MOTIF_DRAG_INITIATOR_INFO and have a data size of 8. This property then should contain information about which targets the initiator is able to serve and what selection atom to use for the data transfer. Table shows the structure of this property.

_MOTIF_DRAG_RECEIVER_INFO

Table: The structure of the _MOTIF_DRAG_INITIATOR_INFO property describes the initiator.

Offset	Size	Description
+0x00	BYTE	Byte Order: either 'B' (MSB first) or 'l' (LSB first).
+0x01	BYTE	Protocol Version of Initiator: currently 0.
+0x02	CARD16	Targets Index: the index of a targets list within the targets table. The first list within the targets list has an index of 0. This index advertises which targets the initiator is willing to handle.
+0x04	CARD32	Selection Atom: atom ID to be used as the selection atom for the data transfer when the drop actually takes place.

Figure finally shows the four properties which are representing an important part of the information infrastructure for the drag and drop mechanism.

Figure: Properties involved in the Drag & Drop game.