1pod::Prima::Clipboard(3U)ser Contributed Perl Documentatipoond::Prima::Clipboard(3)
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NAME

6       Prima::Clipboard - GUI interprocess data exchange
7

DESCRIPTION

9       Prima::Clipboard class is a descendant of Prima::Component.  It serves
10       as an interface to the specific data storage, called clipboard, visible
11       to all clients of one GUI space. The system clipboard is intended for
12       the exchange of information of an arbitrary type between graphic
13       applications.
14

SYNOPSIS

16          my $c = $::application-> Clipboard;
17
18          # paste data
19          my $string = $c-> text;
20          my $image  = $c-> image;
21          my $other  = $c-> fetch('Other type');
22
23          # copy datum
24          $c-> text( $string);
25
26          # copy data
27          $c-> open;
28          $c-> text( $string);
29          $c-> image( $image);
30          $c-> store( $image);
31          $c-> close;
32
33          # clear
34          $c-> clear;
35

USAGE

37       Prima::Clipboard provides access to the system clipboard data storage.
38       For the easier communication, the system clipboard has one 'format'
39       field, that is stored along with the data.  This field is used to
40       distinguish between data formats.  Moreover, a clipboard can hold
41       simultaneously several data instances, of different data formats. Since
42       the primary usage of a clipboard is 'copying' and 'pasting', an
43       application can store copied information in several formats, increasing
44       possibility that the receiving application recognizes the data.
45
46       Different systems provide spectrum of predefined data types, but the
47       toolkit uses only three of these - ascii text, utf8 text, and image. It
48       does not limit, however, the data format being one of these three types
49       - an application is free to register its own formats. Both predefined
50       and newly defined data formats are described by a string, and the three
51       predefined formats are represented by 'Text', 'UTF8', and 'Image'
52       string constants.
53
54       The most frequent usage of Prima::Clipboard is to preform two tasks -
55       copying and pasting. Both can be exemplified by the following:
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57          my $c = $::application-> Clipboard;
58
59          # paste
60          my $string = $c-> text;
61
62          # copy
63          $c-> text( $string);
64
65       This simplistic code hides other aspects of Prima::Clipboard class.
66
67       First, the default clipboard is accessible by an implicit name call, as
68       an object named 'Clipboard'. This scheme makes it easily overridable.
69       A more important point is, that the default clipboard object might be
70       accompanied by other clipboard objects. This is the case with X11
71       environment, which defines also 'Primary' and 'Secondary' system
72       clipboards. Their functionality is identical to the default clipboard,
73       however. "get_standard_clipboards()" method returns strings for the
74       clipboards, provided by the system.
75
76       Second, code for fetching and storing multi-format data is somewhat
77       different.  Clipboard is viewed as a shared system resource, and have
78       to be 'opened', before a process can grab it, so other processes can
79       access the clipboard data only after the clipboard is 'closed' ( Note:
80       It is not so under X11, where there the clipboard locking is advisory,
81       and any process can grab clipboard at any time) .
82
83       "fetch()" and "store()" implicitly call "open()" and "close()", but
84       these functions must be called explicitly for the multi-format data
85       handling. The code below illustrates the said:
86
87           # copy text and image
88           if ( $c-> open) {
89              $c-> clear;
90              $c-> store('Text', $string);
91              $c-> store('Image', $image);
92              $c-> close;
93           }
94
95           # check present formats and paste
96          if ( $c-> open) {
97             if ( $c-> format_exists('Text')) {
98                $string = $c-> fetch('Text');
99             }
100             # or, check the desired format alternatively
101             my %formats = map { $_ => 1 } $c-> get_formats;
102             if ( $formats{'Image'}) {
103                $image = $c-> fetch('Image');
104             }
105
106             $c-> close;
107          }
108
109       The clear() call in the copying code is necessary so the newly written
110       data will not mix with the old.
111
112       At last, the newly registered formats can be accessed by a program:
113
114          my $myformat = 'Very Special Old Pale Data Format';
115          if ( $c-> register_format($myformat)) {
116             $c-> open;
117             $c-> clear;
118             $c-> store('Text', 'sample text');
119             $c-> store($myformat', 'sample ## text');
120             $c-> close;
121          }
122
123   Custom formats
124       Once registered, all processes in a GUI space can access the data by
125       this format. The registration must take place also if a Prima-driven
126       program needs to read data in a format, defined by an another program.
127       In either case, the duplicate registration is a valid event.  When no
128       longer needed, a format can be de-registered.  It is not a mandatory
129       action, however - the toolkit cleans up before exit. Moreover, the
130       system maintains a reference counter on the custom-registered formats;
131       de-registering does not mean deletion, thus. If two processes use a
132       custom format, and one exits and re-starts, it still can access the
133       data in the same format, registered by its previous incarnation.
134
135   Unicode
136       In real life, application often interchange text in both ascii and
137       utf8, leaving the choice to reader programs.  While it is possible to
138       access both at the same time, by "fetch"'ing content of "Text" and
139       "UTF8" clipboard slots, widgets implement their own pasting scheme. To
140       avoid hacking widget code, usage of "text" property is advised instead
141       of indicating 'Text' and 'UTF8' constants. This method is used in
142       standard widgets, and is implemented so the programmer can reprogram
143       its default action by overloading "PasteText" notification of
144       "Prima::Application" ( see "PasteText" in Prima::Application ).
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146       The default action of "PasteText" is to query first if 'Text' format is
147       available, and if so, return the ascii text scalar. If
148       "Prima::Application::wantUnicodeInput" is set, 'UTF8' format is checked
149       before resorting to 'Text'. It is clear that this scheme is not the
150       only possibly needed, for example, an application may want to ignore
151       ASCII text, or, ignore UTF8 text but have
152       "Prima::Application::wantUnicodeInput" set, etc.
153
154       The symmetric action is "CopyText", that allows for a custom text
155       conversion code to be installed.
156
157   Images
158       Image data can be transferred in different formats in different OSes.
159       The lowest level is raw pixel data in display-based format, whereas
160       GTK-based applications can also exchange images in file-based formats,
161       such as bmp, png etc. To avoid further complications in the
162       implementations, "PasteImage" action was introduced to handle these
163       cases, together with a symmetrical "CopyImage".
164
165       The default action of "PasteImage" is to query first if 'Image' format
166       is available, and if so, return the Image object. This by default reads
167       data from raw image buffer, but if fails, on unix the logic proceeds by
168       checking data in formats 'image/bmp', 'image/png' etc.  "BMP" is
169       checked first because the corresponding codec is always compiled in
170       Prima, it doesn't depend on external libraries. Next is checked "PNG"
171       format, because it is lossless, then "TIFF", then all others.
172
173       When storing the image on the clipboard, only the default format, raw
174       pixel data is used.
175

API

177   Properties
178       image OBJECT
179           Provides access to an image, stored in the system clipboard.  In
180           get-mode call, return "undef" if no image is stored.
181
182       text STRING
183           Provides access to text stored in the system clipboard.  In get-
184           mode call, return "undef" if no text information is present.
185
186   Methods
187       clear
188           Deletes all data from clipboard.
189
190       close
191           Closes the open/close brackets. open() and close() can be called
192           recursively; only the last close() removes the actual clipboard
193           locking, so other processes can use it as well.
194
195       deregister_format FORMAT_STRING
196           De-registers a previously registered data format.  Called
197           implicitly for all not de-registered format before a clipboard
198           object is destroyed.
199
200       fetch FORMAT_STRING
201           Returns the data of FORMAT_STRING data format, if present in the
202           clipboard. Depending on FORMAT_STRING, data is either text string
203           for 'Text' format, Prima::Image object for 'Image' format and a
204           binary scalar value for all custom formats.
205
206       format_exists FORMAT_STRING
207           Returns a boolean flag, showing whether FORMAT_STRING format data
208           is present in the clipboard or not.
209
210       get_handle
211           Returns a system handle for a clipboard object.
212
213       get_formats
214           Returns array of strings, where each is a format ID, reflecting the
215           formats present in the clipboard.
216
217           Only the predefined formats, and the formats registered via
218           "register_format()" are returned. There is no way to see if a
219           format, not registered before, is present.
220
221       get_registered_formats
222           Returns array of strings, each representing a registered format.
223           "Text" and "Image" are returned also.
224
225       get_standard_clipboards
226           Returns array of strings, each representing a system clipboard. The
227           default "Clipboard" is always present. Other clipboards are
228           optional.  As an example, this function returns only "Clipboard"
229           under win32, but also "Primary" and "Secondary" under X11. The
230           code, specific to these clipboards must refer to this function
231           first.
232
233       open
234           Opens a system clipboard and locks it for the process single use;
235           returns a success flag. Subsequent "open" calls are possible, and
236           always return 1. Each "open()" must correspond to "close()",
237           otherwise the clipboard will stay locked until the blocking process
238           is finished.
239
240       register_format FORMAT_STRING
241           Registers a data format under FORMAT_STRING string ID, returns a
242           success flag. If a format is already registered, 1 is returned. All
243           formats, registered via "register_format()" are de-registered with
244           "deregister_format()" when a program is finished.
245
246       store FORMAT_STRING, SCALAR
247           Stores SCALAR value into the clipboard in FORMAT_STRING data
248           format. Depending of FORMAT_STRING, SCALAR is treated as follows:
249
250              FORMAT_STRING     SCALAR
251              ------------------------------------
252              Text              text string in ASCII
253              UTF8              text string in UTF8
254              Image             Prima::Image object
255              other formats     binary scalar value
256
257           NB. All custom formats treated as a binary data. In case when the
258           data are transferred between hosts with different byte orders no
259           implicit conversions are made. It is up to the programmer whether
260           to convert the data in a portable format, or leave it as is. The
261           former option is of course preferable. As far as the author knows,
262           the Storable module from CPAN collection provides the system-
263           independent conversion routines.
264

AUTHOR

266       Dmitry Karasik, <dmitry@karasik.eu.org>.
267

SEE ALSO

269       Prima, Prima::Component, Prima::Application
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273perl v5.30.1                      2020-01-30          pod::Prima::Clipboard(3)
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