DtDndProtocol(4)

NAME
DtDndProtocol — drag and drop matching and transfer protocols

DESCRIPTION
The drag and drop protocols provide policy for matching and data transfer between the drag initiator and the drop receiver of file names, selected text spans and application-defined structured data formats.

The drag and drop protocols use the standard X11 selection targets, where available, with the addition of several new selection targets where required.

These protocols provide for the transfer of the following types of data:

    Selected Text File Names Buffers

PROTOCOL OVERVIEW
Each protocol consists of the following:

  Drag and Drop API Protocol
Each protocol described corresponds to a specific DtDndProtocol enumeration value.

  Export/Import Targets
The Motif drag and drop API provides support for matching of the data transfer protocol between the drag initiator and the various drop receivers. This allows the user to determine readily which drop sites will accept the dragged data.

The drag initiator sets the XmNexportTargets resource of the XmDragContext to the list of target atoms that describe the data being dragged. The drop receiver sets the XmNimportTargets resource of the XmDropSite to the list of target atoms that describe the data that it will accept. The Motif drag and drop subsystem allows drops when the XmNexportTargets and XmNimportTargets have at least one target in common.

  Data Transfer Protocol
Once the drag initiator has dropped on the drop receiver, the transfer of data is begun. The transfer is accomplished using X selections and is controlled by the drop receiver.

The drop receiver starts all transfers by converting the selection into the ICCCM TARGETS target to get the set of available selection targets. (See the for a description of converting targets.) It then chooses the appropriate selections from that set and requests that the drag initiator convert each requested selection. Each protocol has a set of selection targets that are used to transfer all the necessary data. These target conversions are usually initiated by calling XmDropTransferStart().

  Move Completion
When the operation of the drop is XmDROP_MOVE, the drop receiver must complete the move using an appropriate method. For most data transfers, this is accomplished by converting the selection into the ICCCM DELETE target to tell the drag initiator that it may delete the data. For most file name transfers, this is accomplished via the file system.

TEXT TRANSFER PROTOCOL
The text transfer protocol is used to exchange text selections.

  Drag and Drop API
This is the protocol used when a DtDndProtocol of DtDND_TEXT_TRANSFER is specified.

  Export/Import Targets
The export or import targets are any of the following; the target describing the character encoding of the text selection, COMPOUND_TEXT, STRING or TEXT.

  Data Transfer Protocol
The transfer of text selections follows the protocols described in the ICCCM manual. If the character encoding of the drag initiator and drop receiver are the same, that target should be converted to get the text selection. If the character encoding are different, the drop receiver should attempt to convert the standard text targets in the following order: COMPOUND_TEXT, STRING or TEXT.

  Move Completion
The move is completed by converting the selection into the ICCCM DELETE target.

FILE NAME TRANSFER PROTOCOL
The transfer protocol is used to exchange file names.

  Drag and Drop API
This is the protocol used when a DtDndProtocol of DtDND_FILENAME_TRANSFER is specified.

  Export/Import Targets
The export or import targets are FILE_NAME and, optionally, _DT_NETFILE if capable of providing the file name in network canonical form using tt_file_netfile(3) and tt_netfile_file(3).

  Data Transfer Protocol
If the ICCCM HOST_NAME target is in the list of target atoms, it is converted. If the returned host name is different than the host name for the drop receiver and the _DT_NETFILE target is in the list of target atoms, it is converted. The drag initiator uses tt_file_netfile(3) to encode the file names and the drop receiver uses tt_netfile_file(3) to decode the file names.

If the hosts are the same for both the drag initiator and the drop receiver or either the HOST_NAME or the _DT_NETFILE targets are not in the list of target atoms from the drag initiator, the drop receiver converts the ICCCM FILE_NAME target. No encoding of the file names occurs in this case.

  Move Completion
Moves of file names can be accomplished atomically using standard file system operations. Drop receivers are encouraged to use the file system. The drop receiver may alternatively choose to use the ICCCM DELETE target to complete the XmDROP_MOVE and the drag initiator must be ready to comply.

BUFFER TRANSFER PROTOCOL
The transfer protocol is used to exchange memory buffers.

  Drag and Drop API
This is the protocol used when a DtDndProtocol of DtDND_BUFFER_TRANSFER is specified.

  Export/Import Targets
The export and import targets are _DT_BUFFER_DATA, _DT_BUFFER_LENGTHS and, optionally, _DT_BUFFER_NAMES.

  Data Transfer Protocol
The _DT_BUFFER_DATA and _DT_BUFFER_LENGTHS targets are converted to transfer the buffer data.

The data of the buffers is encoded into the _DT_BUFFER_DATA target as an array of bytes. The lengths in bytes of each buffer are encoded into _DT_BUFFER_LENGTHS. Each length is used to index into the _DT_BUFFER_DATA array.

If the _DT_BUFFER_NAMES target is available, it is converted to transfer the names of the buffers.

  Move Completion
The move is completed by converting the selection into the ICCCM DELETE target.

SELECTION TARGETS
The following table describes the selection targets used in the drag and drop data matching and transfer protocols.
Atom | Type | Description
TARGETS | ATOM | A list of valid target atoms. See ICCCM section 2.6.2.
DELETE | NULL | Used to delete the dropped data. If the drop receiver wishes to perform a move operation on the data, after copying the data it should request conversion of the target. See ICCCM section 2.6.3.1.
COMPOUND_TEXT | COMPOUND_TEXT | The text selection in compound text format. See ICCCM section 2.7.1.
STRING | STRING | The text selection in ISO Latin-1 format. See ICCCM section 2.7.1.
TEXT | TEXT | The text selection in the format preferred by the selection holder. See ICCCM section 2.7.1.
HOST_NAME | TEXT | The name of the machine running the client as seen from the machine running the server. See ICCCM section 2.6.2.
FILE_NAME | TEXT | The full path name of the files. See ICCCM section 2.6.2.
_DT_NETFILE | TEXT | The full pathname of the files, each encoded using and decoded using
_DT_BUFFER_DATA | _DT_BUFFER_DATA | The buffer data in an array of bytes.
_DT_BUFFER_LENGTHS | INTEGER | The lengths in bytes of each buffer in the array.
_DT_BUFFER_NAMES | STRING | The names of each buffer, suitable for use as a file name.

SEE ALSO
DtDnd(5), DtDndDragStart(3), DtDndVaDragStart(3), DtDndVaDropRegister(3), DtDndDropUnregister(3), DtDropTransferStart(3), XmDragContext(3), XmDragStart(3), XmDropRegister(3), XmDropSite(3), tt_file_netfile(3), tt_netfile_file(3), X11/R5 Inter-Client Communications Conventions Manual (ICCCM)