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1 @c -*-texinfo-*-
2 @c This is part of the XEmacs Lisp Reference Manual.
3 @c Copyright (C) 1998 Oliver Graf <ograf@fga.de>
4 @c Original reference is (c) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc.
5 @c See the file lispref.texi for copying conditions.
6 @setfilename ../../info/dragndrop.texi
7 @node Drag and Drop, Modes, Scrollbars, Top
8 @chapter Drag and Drop
9 @cindex drag and drop
10
11 @emph{WARNING}: the Drag'n'Drop API is still under development and the
12 interface may change! The current implementation is considered experimental.
13
14 Drag'n'drop is a way to transfer information between multiple applications.
15 To do this several GUIs define their own protocols. Examples are OffiX, CDE,
16 Motif, KDE, MSWindows, GNOME, and many more. To catch all these protocols,
17 XEmacs provides a generic API.
18
19 One prime idea behind the API is to use a data interface that is
20 transparent for all systems. The author thinks that this is best
21 archived by using URL and MIME data, cause any internet enabled system
22 must support these for email already. XEmacs also already provides
23 powerful interfaces to support these types of data (tm and w3).
24
25 @menu
26 * Supported Protocols:: Which low-level protocols are supported.
27 * Drop Interface:: How XEmacs handles a drop from another application.
28 * Drag Interface:: Calls to initiate a drag from XEmacs.
29 @end menu
30
31 @node Supported Protocols
32 @section Supported Protocols
33
34 The current release of XEmacs only support a small set of Drag'n'drop
35 protocols. Some of these only support limited options available in the API.
36
37 @menu
38 * OffiX DND:: A generic X based protocol.
39 * CDE dt:: Common Desktop Environment used on suns.
40 * MSWindows OLE:: Mr. Gates way of live.
41 * Loose ends:: The other protocols.
42 @end menu
43
44 @node OffiX DND
45 @subsection OffiX DND
46 @cindex OffiX DND
47
48 @emph{WARNING}: If you compile in OffiX, you may not be able to use
49 multiple X displays successfully. If the two servers are from
50 different vendors, the results may be unpredictable.
51
52 The OffiX Drag'n'Drop protocol is part of a X API/Widget library created by
53 Cesar Crusius. It is based on X-Atoms and ClientMessage events, and works with
54 any X platform supporting them.
55
56 OffiX is supported if 'offix is member of the variable dragdrop-protocols, or
57 the feature 'offix is defined.
58
59 Unfortunately it uses it's own data types. Examples are: File, Files,
60 Exe, Link, URL, MIME. The API tries to choose the right type for the data that
61 is dragged from XEmacs (well, not yet...).
62
63 XEmacs supports both MIME and URL drags and drops using this API. No application
64 interaction is possible while dragging is in progress.
65
66 For information about the OffiX project have a look at http://leb.net/~offix/
67
68 @node CDE dt
69 @subsection CDE dt
70 @cindex CDE dt
71
72 CDE stands for Common Desktop Environment. It is based on the Motif
73 widget library. It's drag'n'drop protocol is also an abstraction of the
74 Motif protocol (so it might be possible, that XEmacs will also support
75 the Motif protocol soon).
76
77 CDE has three different types: file, buffer, and text. XEmacs only uses
78 file and buffer drags. The API will disallow full URL drags, only file
79 method URLs are passed through.
80
81 Buffer drags are always converted to plain text.
82
83 @node MSWindows OLE
84 @subsection MSWindows OLE
85 @cindex MSWindows OLE
86
87 Only allows file drags and drops.
88
89 @node Loose ends
90 @subsection Loose ends
91
92 The following protocols will be supported soon: Xdnd, Motif, Xde (if I
93 get some specs), KDE OffiX (if KDE can find XEmacs windows).
94
95 In particular Xdnd will be one of the protocols that can benefit from
96 the XEmacs API, cause it also uses MIME types to encode dragged data.
97
98 @node Drop Interface
99 @section Drop Interface
100 @cindex drop
101 @cindex Drop API
102
103 For each activated low-level protocol, a internal routine will catch
104 incoming drops and convert them to a dragdrop-drop type
105 misc-user-event.
106
107 This misc-user-event has its function argument set to
108 @code{dragdrop-drop-dispatch} and the object contains the data of the drop
109 (converted to URL/MIME specific data). This function will search the variable
110 @code{experimental-dragdrop-drop-functions} for a function that can handle the
111 dropped data.
112
113 To modify the drop behavior, the user can modify the variable
114 @code{experimental-dragdrop-drop-functions}. Each element of this list
115 specifies a possible handler for dropped data. The first one that can handle
116 the data will return @code{t} and exit. Another possibility is to set a
117 extent-property with the same name. Extents are checked prior to the
118 variable.
119
120 The customization group @code{drag-n-drop} shows all variables of user
121 interest.
122
123 @node Drag Interface
124 @section Drag Interface
125 @cindex drag
126 @cindex Drag API
127
128 This describes the drag API (not implemented yet).