This command provides an interface to the X selection mechanism and
implements the full selection functionality described in the
X Inter-Client Communication Conventions Manual (ICCCM).
The widget object used to invoke the methods below determines which
display is used to access the selection.
In order to avoid conflicts with selection methods of widget classes
(e.g. Text) this set of methods uses the prefix Selection.
The following methods are currently supported:
$widget->SelectionClear?(-selection=>selection)?
If selection exists anywhere on $widget's display, clear it
so that no window owns the selection anymore. Selection
specifies the X selection that should be cleared, and should be an
atom name such as PRIMARY or CLIPBOARD; see the Inter-Client
Communication Conventions Manual for complete details.
Selection defaults to PRIMARY.
Returns an empty string.
Retrieves the value of selection from $widget's display and
returns it as a result. Selection defaults to PRIMARY.
Type specifies the form in which the selection is to be returned
(the desired ``target'' for conversion, in ICCCM terminology), and
should be an atom name such as STRING or FILE_NAME; see the
Inter-Client Communication Conventions Manual for complete details.
Type defaults to STRING. The selection owner may choose to
return the selection in any of several different representation
formats, such as STRING, ATOM, INTEGER, etc. (this format is different
than the selection type; see the ICCCM for all the confusing details).
If format is not STRING then things get messy, the following
description is from the Tcl/Tk man page as yet incompetely translated for
the perl version - it is misleading at best.
If the selection is returned in a non-string format, such as INTEGER
or ATOM, the SelectionGet converts it to a list of perl
values: atoms are converted to their
textual names, and anything else is converted integers.
A goal of the perl port is to provide better handling of different
formats than Tcl/Tk does, which should be possible given perl's
wider range of ``types''. Although some thought went into this
in very early days of perl/Tk what exactly happens is still
``not quite right'' and subject to change.
Creates a handler for selection requests, such that callback will
be executed whenever selection is owned by $widget and
someone attempts to retrieve it in the form given by type
(e.g. type is specified in the selection get command).
Selection defaults to PRIMARY, type defaults to STRING, and
format defaults to STRING. If callback is an empty string
then any existing handler for $widget, type, and
selection is removed.
When selection is requested, $widget is the selection owner,
and type is the requested type, callback will be executed
with two additional arguments.
The two additional arguments
are offset and maxBytes: offset specifies a starting
character position in the selection and maxBytes gives the maximum
number of bytes to retrieve. The command should return a value consisting
of at most maxBytes of the selection, starting at position
offset. For very large selections (larger than maxBytes)
the selection will be retrieved using several invocations of callback
with increasing offset values. If callback returns a string
whose length is less than maxBytes, the return value is assumed to
include all of the remainder of the selection; if the length of
callback's result is equal to maxBytes then
callback will be invoked again, until it eventually
returns a result shorter than maxBytes. The value of maxBytes
will always be relatively large (thousands of bytes).
If callback returns an error (e.g. via die)
then the selection retrieval is rejected
just as if the selection didn't exist at all.
The format argument specifies the representation that should be
used to transmit the selection to the requester (the second column of
Table 2 of the ICCCM), and defaults to STRING. If format is
STRING, the selection is transmitted as 8-bit ASCII characters (i.e.
just in the form returned by command).
If format is not STRING then things get messy, the following
description is from the Tcl/Tk man page as yet untranslated for
the perl version - it is misleading at best.
If format is
ATOM, then the return value from command is divided into fields
separated by white space; each field is converted to its atom value,
and the 32-bit atom value is transmitted instead of the atom name.
For any other format, the return value from command is
divided into fields separated by white space and each field is
converted to a 32-bit integer; an array of integers is transmitted
to the selection requester.
The format argument is needed only for compatibility with
many selection requesters, except Tcl/Tk. If Tcl/Tk is being
used to retrieve the selection then the value is converted back to
a string at the requesting end, so format is
irrelevant.
A goal of the perl port is to provide better handling of different
formats than Tcl/Tk does, which should be possible given perl's
wider range of ``types''. Although some thought went into this
in very early days of perl/Tk what exactly happens is still
``not quite right'' and subject to change.
$widget->SelectionOwner?(-selection=>selection)?
SelectionOwner returns the
window in this application that owns selection on the display
containing $widget, or an empty string if no window in this
application owns the selection. Selection defaults to PRIMARY.
SelectionOwn causes $widget to become
the new owner of selection on $widget's display, returning
an empty string as result. The existing owner, if any, is notified
that it has lost the selection.
If callback is specified, it will be executed when
some other window claims ownership of the selection away from
$widget. Selection defaults to PRIMARY.
KEYWORDS
clear, format, handler, ICCCM, own, selection, target, type