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From: [email protected] (Peter Prymmer)
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Subject: comp.lang.perl.tk FAQ part2 of 5
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Date: Mon, 09 Dec 1996 00:28:40 GMT
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Perl/Tk FAQ part 2 of 5 - Programming
*************************************
______________________________________________________________________



9. How do I get widget X to do Y ?

There are a number of tasks that can be accomplished with perl/Tk
widgets, configurations, and bindings (a few that can't and a few that
require specific tricks). Beginners are encouraged to work through the
examples in UserGuide.pod. Some examples from UserGuide.pod
are addressed in this document among those that follow.

Basically a widget can be "created" by simply calling the sub of the same
name:

    my $main = new MainWindow;

will set aside the necessary system memory etc. for a new MainWindow
widget (it does not appear until after the MainLoop; call). The object
"created" is then callable via the variable $main. So, for example, if you
wanted a Button in your MainWindow, then this:

    $main->Button();

would be a very basic example of a widget command. If you wanted to
later call this button widget you would need a "widget tag or ID" to "get a
handle on it". Instead of the above call try something like:

    my $button = $main->Button();

The variable $button is how you refer to the Button widget in
subsequent calls, such as when we call the pack routine:

    $button -> pack;

A complete script that incorporates these ideas to make a very plain
button would look like:

    #!/usr/bin/perl -w
    use Tk;
    use strict;
    my $main = new MainWindow;
    my $button = $main -> Button();
    $button -> pack;
    MainLoop;

But who wants such a plain looking button? You can provide a number of
different widget configurations via calls to the configure routine as in:

    #!/usr/bin/perl -w
    use Tk;
    use strict;
    my $main = new MainWindow;
    my $button = $main->Button();
    $button -> configure(-text => 'Press me!');
    $button -> pack;
    MainLoop;

The Perl motto is "there is more than one way to do it." - perl/Tk
remains quite true to this motto as well. Note that the above script could
have been written quite succinctly without the use of either the $main or
$button variables as:

    #!/usr/bin/perl -w
    use Tk;
    use strict;
    new MainWindow -> Button(-text => 'Press me!') -> pack;
    MainLoop;

But if you want your widgets to actually do things then you must set up
callback procedures as discussed later...

As of Tk-b9(.01) the - sign in front of some options (like -text in the
above example) will be optional (hence ->Button(text => 'Press
me!')) would work. As of the version of Perl/Tk that supercedes
Tk-b11.02 the - sign may again be required. In any case it is best to code
with it especially if it is necessary. Another commonly overlooked
problem is that elements in a hash are supposed to be strings hence a
configuration option like -length +> 5, really ought to be specified as
either '-length' +> 5, or "-length" +> 5, etc.

______________________________________________________________________



9.1. How do I get a Button to call a Perl subroutine?

You may specify the -command option in the call to create & pack the
button as in:

    $main->Button(-text => 'Print',
                   -command => sub{do_print($filename, $font)}
                   )->pack;

Where sub do_print { } is a subroutine that handles two arguments
and is declared elsewhere in the script. A full script example of the use of
the above code is presented in the second example(s) in UserGuide.pod

(Full source code for this and other examples from UserGuide.pod may
be found at http://w4.lns.cornell.edu/~pvhp/ptk/pod/. To load code from
the web save as a local file say ex1.pl, edit the first line to point to your
perl interpreter, then change permission: %chmod u+x ex1.pl, then
execute the script: %ex1.pl.)

The above method is called the "anonymous subroutine (closure)"
method. As discussed in Callback.pod one might have re-written that
statement to use the "reference to a sub" method thusly:

    $main->Button(-text => 'Print',
                   -command => [ \&do_print , $filename, $font ]
                   )->pack;

Note the backslash in front of \&do_print. This causes perl to generate
a reference to sub do_print rather than call it. (thanks Jim Stern :-)

______________________________________________________________________



9.2. How do I get a Button to actively change under my mouse pointer?

You should specify both an '-image' and an '-activeimage'
configuration option either when calling the ->Button() method or in
a later separate call to the ->configure() method.

Here is an example excerpted from the basic_demo script that comes
with the Tk kit:

    #!/usr/local/bin/perl -w

    use Tk;

    $main = MainWindow->new;

    $QPBFile  = "demos/images/QuitPB.xpm";
    $QPBaFile = "demos/images/QuitPBa.xpm";

    $QuitPB  = $main->Pixmap('-file' => Tk->findINC("$QPBFile"));
    $QuitPBa = $main->Pixmap('-file' => Tk->findINC("$QPBaFile"));

    my $but  = $main->Button('-image'       => $QuitPB,
                             '-activeimage' => $QuitPBa,
                             '-command'     => sub { $main->destroy }
                            ) -> pack;

    MainLoop;

    __END__


______________________________________________________________________



9.3. How do I arrange the layout of my widgets?

To control the layout and appearance of widgets in a window one makes
use of a geometry manager, as well as -padding, -fill, -expand, and
-anchor options of individual widgets.

A geometry manager is any Tk procedure for controlling the
arrangement of widgets in your application window. The predominant
geometry manager used in both Tcl/Tk and perl/Tk is pack also known
informally as the "packer" (other geometry managers are the "placer"
and the canvas widget itself but are much less popular. There is also
Nick Ing-Simmon's Table widget [discussed in a later question] and
BLT_Table [which made it's way into perl/Tk thanks to Guy Decoux -
but is also discussed in a later question]. So far tixForm is for Tcl/Tk
only, but a perl/Tk version of Tix is in the works. You can invoke pack at
the time of widget creation via calls like:

    $widget->pack;

where widget can be any of the perl/Tk widget primitives. Widget option
lists are usually passed as an associative array (hash) in parentheses
thusly:

    $widget(-option0 => value0,-option1 => value1)->pack;

pack is often used in conjunction with the frame container widget to
arrange your widgets much like a hiearchically arranged set of window
panes (ultimately in a rectangular "tiling" fashion of sorts). An example
of this would be:

    my $top2 = $main->Toplevel;
    my $frame = $top2->Frame;
    $frame->pack;
    $frame->Label(-text => 'Left2')->pack(-side => 'left');
    $frame->Label(-text => 'Right2')->pack(-side => 'right');
    $top2->Label(-text => 'Bottom2')->pack(-side => 'bottom');
    MainLoop;

Note that pack itself is given parameters in this example. The default
behavior for pack is equivalent to specifying -side => 'top' which
can be overridden as in the above example.

(Full source code for this and other examples from UserGuide.pod may
be found at http://w4.lns.cornell.edu/~pvhp/ptk/pod/. To load code from
the web save as a local file say ex2.pl, edit the first line to point to your
perl interpreter, change permission using: chmod u+x ex2.pl, then
type the name of your script: ex2.pl.)

One of the more helpful options to pass to pack when trying to get a
given widget layout "just right" is through padding: either -padx or
-pady. The details of the use of pad depend on which specific widget
you are trying to pack. In fact you can often add the -pad in the call to
create the widget rather than in the call to pack.

There is also the -anchor configuration option for widgets. A good
introduction to the 9 possible -anchor (and -overanchor) values is
given by the popup demo in your perl/Tk build directory.

When setting a widget within a frame next to another widget one may
wish to make use of the -fill => 'style' (where style = none | x |
y | both) options of either pack or the widget itself. A typical
situation where this is used is in setting up the Scrollbar next to a
Canvas or Text widget.

Another aspect to consider when laying out your widgets is their
behavior under resize operations (grabbing a part of the window frame
and making it bigger or smaller - details depend on your window
manager). This may be controlled by the -expand option of either pack
or the widget itself.

______________________________________________________________________



9.4. How do I get a Popup to popup?

For things like a simple "are you sure?" dialog box you might want to
take a look at Dialog.pm which is discussed in a later question within
this FAQ [15.1].

If you don't wish to require Tk::Dialog, you need something more
complicated, or you simply want to create your own independent window
with widgets; you must first setup a Toplevel in perl/Tk. The fourth
example in UserGuide.pod gives a simple example of how to call
Toplevel. Quoting from that script:

    my $main = new MainWindow;
    fill_window($main, 'Main');
    my $top1 = $main->Toplevel;

Where sub fill_window is declared after the call to MainLoop;.
When running that script take careful note of which window pops up
first, which window has grabbed the active attention of your input
device(s), and which widget within the active window has the
keyboard/mouse focus when all three windows are open.

The use of Toplevels brings up the issue of grab - or which
independent window is presently "active" and which are activatable. To
make a Toplevel window active call grab thusly:

    $Top_widget->grab(grab_option);

where $Top_widget identifies the desired Toplevel (it would be
either $top1 or $top2 in the sample script referred to above).
grab_option could be -global - but this is discouraged as a sign of
"desparate programming style". To give a Toplevel "local grab" you
may simply say:

    $Top_widget->grab;

That is, without an argument.

The use of Toplevels may also bring up the issue of focus - or which
window - even which widget within a window - is presently "hot". You
may call focus on an entire Toplevel:

    $Top_widget->focus;

However, focus is most often used with individual widgets rather than a
whole Toplevel.

To de-iconify a widget there is in fact a Popup function that may be
called thusly:

    $Top_widget->Popup();

______________________________________________________________________



9.5. How do I bind keyboard keys?

There are many default key bindings built in to the widgets of perl/Tk.
Making proper use of them often involves setting up the right callback.
(You may wish to consult the examples in BindTable.pod for help
with this subject.)

The basic idea is:

    $widget -> bind('<keyname>' => action);

Where $widget is the tag or ID of the widget for which the bindings
are to hold (note for global bindings you have to bind to <All>, for
semi-global bindings you need to bind to all the relevant widgets in your
application), '<keyname>' can be things like:

    <Key> or <KeyPress> or <Any-KeyPress>
    <KeyRelease>
    <Button> or <ButtonPress>
    <ButtonRelease>
    <Button-1> or <B1>
    <Double-1>
    <Enter>
    <Leave>
    <Motion>

To figure out what names perl/Tk uses for such <bindings> use the
"binder-finder" on a widget's .pm file. For example, you could find
bindings hidden inside of Button.pm by typing this at your shell
prompt:

    perl -ne 'print if s/.*(<[^>]*>).*/$1/g;' Button.pm

while in the directory where Button.pm is located (and if you are not
there then simply specify the /path/to/Button.pm). Note that due to
inheritance (e.g.the type of script bindings that are being discussed here)
what the binder-finder turns up may not be the last word on a given
widget's behaviour. This may be especially true for a widget inside of a
compound/composite widget. Note also that the binder-finder will turn
up things like <FILEHANDLES> as well as honest <Bindings>.
Discrimination in its use is called for (and while your at it you could have
just as easily used an editor and actually examined the code directly now
couldn't you?).

To get an idea of what the code is for a key that you are interested in try
running the xlib_demo that comes in your perl/Tk build directory. Hold
your mouse pointer over the window that appears and simply type the
key that you are interested in. The code should appear in the window. If
you do not have perl/Tk up and running yet try "xmodmap -pk" or look
directly at the /usr/include/X11/keysymdef.h file where keysym
names are given with an XK_ pre-pended. Do not try things like the
Tcl/Tk %k symbols in perl scripts. %Ks will be mis-interpreted as
non-existant perl hashes. Instead look at the Xevent function.

Ali Corbin <[email protected]> recently posted a great
little script for determining keyboard key bindings on a MainWindow:

    #!/usr/local/bin/perl -w
    use Tk;
    $top = MainWindow->new();
    $frame = $top->Frame( -height => '6c', -width => '6c',
                            -background => 'black', -cursor => 'gobbler' );
    $frame->pack;
    $top->bind( '<Any-KeyPress>' => sub
    {
        my($c) = @_;
        my $e = $c->XEvent;
        my( $x, $y, $W, $K, $A ) = ( $e->x, $e->y, $e->K, $e->W, $e->A );

        print "A key was pressed:\n";
        print "  x = $x\n";
        print "  y = $y\n";
        print "  W = $K\n";
        print "  K = $W\n";
        print "  A = $A\n";
    } );
    MainLoop();

To bind the action of one widget to that of another try taking a look at
the .pm file for the widget of interest - is there a binding function
already defined? If so you may use it. An example would be the use of
"Up" & "Down" Buttons for a Listbox: one could bind the Buttons
to call Tk::Listbox::UpDown, however, Guy Decoux describes a
much more clever way to use the <Up> and <Down> already defined in
Listbox.pm (this does not work with Tk-b9.01):

    #!/usr/local/bin/perl
    use Tk;
    $top = MainWindow->new;
    $lb = $top->Listbox(-height => 10);
    for($i=0; $i < 120; $i++) {
      $lb->insert('end', $i);
    }
    $f = $top->Frame;
    $up = $f->Button(
           -text => "Up",
           -command => [ $lb->bind(ref $lb, '<Up>'), $lb]
           );
    $down = $f->Button(
             -text => "Down",
             -command =>sub {&{$lb->bind(ref $lb, '<Down>')}($lb)}
             );
    $up->pack(-side => 'left');
    $down->pack;
    $f->pack;
    $lb->pack;
    MainLoop;

______________________________________________________________________



9.6. How do I add bindings?

On Fri, 15 Sep 95 10:30:56 BST Nick Ing-Simmons
<[email protected]> writes:


Re: Multiple binds to a single widget?
**************************************

On Thu, 14 Sep 1995 14:57:54 -0400
Alain St <[email protected]> writes:
!In the tcl/tk doc I have, they say that prepending the script
!with '+' appends the new binding to the current one.
!
!How do I do that in perlTk?
!

 You cannot do that that way (yet?) - one issue is what it would
 mean to prepend '+' to a perl/Tk callback :

    $widget->bind('<A>','+',[\&subname,$arg]);
    # did not look right to me

 Other issue is that I would need to manage a list-of-callbacks in
 glue code.

 Bind your new command to a new tag:

    $widget->bind('Extra',....);

 And add Extra to the widgets bindtags:

    $widget->bindtags([ref($widget),$widget,'Extra',
                        $widget->toplevel,'all']);

______________________________________________________________________



9.7. How do I bind the action of a slider (sic) to ... ?

Technically speaking they are called Scrollbars (not sliders) and one
must configure the action of the desired widget to call the Scrollbar
s (i.e. bind is not involved here)

A common task using Scrollbars is to configure things like Canvas,
Listbox, or a Text widgets to be updated (change appearance) when
the slider of the acompanying Scrollbar is moved by the user.

As an example consider the code that sets up a twelve element Listbox
and an accompanying vertical Scrollbar:

    my $main = new MainWindow;
    my $box = $main->Listbox(-relief => 'sunken',
                             -width => -1, # Shrink to fit
                             -height => 5,
                             -setgrid => 'yes');
    my @items = qw(One Two Three Four Five Six Seven
                   Eight Nine Ten Eleven Twelve);
    foreach (@items) {
       $box->insert('end', $_);
    }
    my $scroll = $main->Scrollbar(-command => ['yview', $box]);

So far so good. But merely setting them up does not mean that the
Listbox even knows that the Scrollbar is lying next to it. Note that
the scalar variable $scroll is how we refer to the Scrollbar, thus,
hooking the $box up to handle $scroll events is a matter of configur
ation:


    $box->configure(-yscrollcommand => ['set', $scroll]);

A complete script that makes use of this code (and adds the necessary
calls to pack and MainLoop;) is given as the fifth example in
UserGuide.pod (and may be found at
http://w4.lns.cornell.edu/~pvhp/ptk/pod/.)

There was an old Perl/Tk tendency to have a bunch of ScrlFoo widgets
(such as ScrlListbox). The use of such widgets is now deprecated in
favor of a new Scrolled class, as in:

    $w = $patent->Scrolled('Text',...);

The widgets that can be ->Scrolled() include:

 o Canvas (::Axis)
 o Entry
 o Ghostview
 o HList
 o HTML (::Web)
 o Listbox
 o Pod
 o Text (::ROText) (::TextUndo)
 o Tiler

______________________________________________________________________



9.8. How do I configure a Scrollbar to scroll multiple widgets?

Note that the widget type that you wish to scroll can be important as a
scroll "unit" on a Text or Listbox may be a character (several pixels -
depending on font) whereas it would be an X "units" on a Canvas (could
be pixel - but you may also specify other units).

A concrete answer for scrolling 3 Listboxes comes courtesy of
Frederick L. Wagner <[email protected]>:

 From a working example of multi-xscrolling:

    sub multiscrollx
    {  # multiscrollx
     my ($sb,$wigs,@args) = @ARG;
     my $w;
     foreach $w (@$wigs)
     {
       $w->xview(@args);
     }
    }  # multiscrollx

    # %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

      $sh->configure( -command => [ \&multiscrollx, $sh,
                         [$scratchrule,$ruleheader,$ruletable]]);
      $ruletable->configure(  -xscrollcommand => [ 'set', $sh]);
      $ruleheader->configure( -xscrollcommand => [ 'set', $sh]);
      $scratchrule->configure(-xscrollcommand => [ 'set', $sh]);

 In this case,
 $sh is a horizontal Scrollbar,
 $ruletable and $scratchrule are Tables
 $ruleheader is an Entry

 However, this approach is good for any widget with X-scrolling
 capability, I think. So the Y counterpart should be:

    sub multiscrolly
    {  # multiscrolly
     my ($sb,$wigs,@args) = @ARG;
     my $w;
     foreach $w (@$wigs)
     {
       $w->yview(@args);
     }
    }  # multiscrolly

    # %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

      $sv->configure( -command => [ \&multiscrolly, $sv,
                                    [$l1,$l2,$l3]]);
      $l1->configure( -yscrollcommand => [ 'set', $sv]);
      $l2->configure( -yscrollcommand => [ 'set', $sv]);
      $l3->configure( -yscrollcommand => [ 'set', $sv]);

 Hope that helps.

Greg VanSickle <[email protected]> points out that this little script
snippet does not provide for the binding of '<Button-2<' that he is
accustomed to. He wrote a package called DSListbox to address this
binding issue.

Conversely, Jong Park asked how to setup multiple Scrollbars to scroll
the same widget. Nick Ing-Simmon's reply makes use of an anonymous
sub and can be summed up in a little script that scrolls a Text widget (to
see the scrolling in action type more than 20 lines of text into the
widget):

    #!/usr/local/bin/perl -w

    use Tk;
    my $mw = MainWindow->new();

    my $s1 = $mw->Scrollbar(-orient => 'vertical');
    my $s2 = $mw->Scrollbar(-orient => 'vertical');

    $s1->pack(-side => 'left', -fill => 'y');
    my $t = $mw->Text(
        -yscrollcommand =>  sub{$s1->set(@_), $s2->set(@_)},
        -wrap           => 'word',
        -width          => 70,
        -height         => 20,
        -font           => $font,
        -setgrid        => 1,
    )->pack(-side => 'left');
    $s2->pack(-side => 'right', -fill => 'y');
    $s1->configure(-command => [$t => 'yview']);
    $s2->configure(-command => [$t => 'yview']);

    MainLoop;

    __END__

______________________________________________________________________



9.9. How do I display a bitmap?

You can display X bitmaps on your widgets with the -bitmap
configuration option. Typically -bitmaps are configured into Label,
Frame, Button, etc. widgets (Canvas widgets are another story however
see question [10.1] below). In order to emphasize the bitmap option itself
let us assume we were specifying a bitmap for a Label with a call like:

    $main->Label(-bitmap => 'bitmap-name')->pack;

Where bitmap-name could be any of the built in Tk bitmaps: error,
gray25, gray50, hourglass, info, question, questhead, warning
(see the widget demo for a full list).

In order to use some of the bitmaps in the perl5/Tk/demos/images/
directory you would specify a fuller path name like:

    $main->Label(-bitmap => "\@$tk_library/demos/images/face")->pack;

Note the escaped "\@" on the directory specification (as well as the use
of the $tk_library variable imported by use Tk;). If you wanted to
specify a file called foobar.xbm in the directory where you were
running the script then either:

    $main->Label(-bitmap => '@foobar.xbm')->pack;
#or
    $main->Label(-bitmap => "\@foobar.xbm")->pack;

should work just fine. In another directory however that would be a
problem. So something like:

    $main->Label(-bitmap => "\@$ENV{'HOME'}/img/foobar.xbm")->pack;

will help someone who has an img/foobar.xbm file in their $HOME
directory. If you don't mind the non-portability then hard-wiring in the
full path name will help as well. (Or if you have write access then put
your files in Tk/demos/images/ e.g.)

______________________________________________________________________



9.10. How do I display an image?

You will want to get a "Photo" handle on the file as in the following
example where 'imggif' is the Photo handle for a gif file that is
distributed with perl/Tk:

    #!/usr/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;

    $main ->Label(-text => 'Main')->pack;
    $main -> Photo('imggif',
                   -file => "$Tk::tk_library/demos/images/earth.gif");
    my $l = $main->Label('-image' => 'imggif')->pack;

    $main->Button(-text => 'close',
                  -command => sub{destroy $main}
                  )->pack(-side => 'left');
    $main->Button(-text => 'exit',
                  -command => [sub{exit}]
                  )->pack(-side => 'right');
    MainLoop;

(Canvas widgets are another story however see question a later question
within this FAQ).

______________________________________________________________________



9.11. What Image types are available?

In addition to the Tk builtin bitmaps there is support for reading images
from files in formats such as: X11 Bitmaps (.xbm), X Pixmaps (.xpm),
and Graphics Inline Format (.gif). See the CrtPhImgFmt man page for
more info (if you have Tk 4.X installed). (In order to support other
formats you might also consider running through a netpbm filter.)

For perl generation of images see the question (later in this FAQ) on
graphics modules.

______________________________________________________________________



9.12. Is there any way to have more than one Listbox contain a
selection?

To allow more than one Listbox to contain a "selection", (or at least a
highlighted item - which need not be the actual selection) specify the
configuration option:

    -exportselection => 0

which will dis-associate Listbox's selection from X selection (only one
window can have X selection at a time).

Here is a rather simple script that illustrates what happens when only
one Listbox has -exportselection => 0 specified:

    #!/usr/bin/perl -w

    use Tk;

    my $main = MainWindow->new;

    my @fruits = ('Apple','Banana','Cherry','Date','Elderberry','Fig');
    my @nuts   = qw(Almond Brazil Chestnut Doughnut Elmnut Filbert);

    my $fruit_list = $main->Listbox();
    for (@fruits) { $fruit_list -> insert('end',$_); }
    $fruit_list->pack();
    my $fruitprint_button = $main->Button(
                              -text => "print selection",
                              -command => sub{ printthem($fruit_list) }
                                          )->pack;

    my $nut_list = $main->Listbox(
                                  -selectmode => 'multiple',
                                  -exportselection => 0,
                                 )->pack;
    for (@nuts) { $nut_list -> insert('end',$_); }
    my $nutprint_button = $main->Button(
                              -text => "print selection(s)",
                              -command => sub{ printthem($nut_list) }
                                          )->pack;

    my $quit_button = $main->Button(-text => "quit program",
                                    -command => sub{exit},
                                    )->pack();

    MainLoop;

    sub printthem {
        my $list = shift;
        my @entries = $list->curselection;
        for (@entries) { print $list -> get($_),"\n";}
    }

For a more extensive example of Listbox usage combined with some
perl data structure exploitation see the script at:

    http://w4.lns.cornell.edu/~pvhp/ptk/etc/lb-constructor

______________________________________________________________________



9.13. How do I select a range of tags in a Text widget?

A question arose concerning getting a range of selections from a Text
widget. Nick Ing-Simmons' answer mentions several possibilities
including:

 Keyboard Copy/Paste 'is' implemented of course...


Subj:   RE: $Text->tag('ranges', 'sel') - does this work?

In <[email protected]>
On Fri, 29 Dec 1995 14:57:42 -0500
Charles J Williams <[email protected]> writes:
!I was writing a little tk perl today, and i decided to try to
!implement a copy/paste using the 'sel' tag
!
!I enabled exportselection, and then try to probe the select
!region with:
!
!    $buffer = $text->tag('ranges', 'sel');
!
!$buffer comes back with one entry, the end of the selection.

 That is to be expected - the scalar gets assigned the last element of
 the list.


!I tried:
!
!    @buffer = $text->tag('ranges', 'sel');
!
!same difference.

 This seems to work for me:

    ($start,$end) = $text->tagRanges('sel');

 In perl/Tk ->tagRanges(...) is an alias for
 ->tag('ranges',...)

 The following subroutine can also probe and print the tagRanges:

    sub showsel
    {
     my $text = @_;
     my @info = $text->tagRanges('sel');
     if (@info)
      {
       print "start=$info[0] end=$info[1]\n"
      }
    }

______________________________________________________________________



9.14. How do I group Radiobuttons together?

Specify the -variable option on each one. Here is an example pulled
from the icon.pl demo script:

     $letters = '';
     my $w_frame_left_b3 = $w_frame_left->Radiobutton(
         -bitmap   => "\@$tk_library/demos/images/letters",
         -variable => \$letters,
         -value    => 'full',
     );
     my $w_frame_left_b4 = $w_frame_left->Radiobutton(
         -bitmap   => "\@$tk_library/demos/images/noletters",
         -variable => \$letters,
         -value    => 'empty',
     );

______________________________________________________________________



9.15. How do I specify fonts?

The quick answer is to specify the font configuration option of your
widget as in:

    #!/usr/local/bin/perl -w
    use Tk;
    $main = MainWindow->new();
    $labl = $main -> Label('-text' => "Foo", '-font' => "fixed");
    $labl -> pack;
    MainLoop;

The long answer involves figuring out what fonts you have access to
locally. The Unix programs xlsfonts and xfontsel are useful in this regard.

The perl/Tk version of xfontsel was distributed as the font_test script
in the Tk build directory.

See also the later question (within this FAQ) on international fonts.

______________________________________________________________________



9.16. How do I get the entry in an Entry?

You want to call get on the return value of the widget itself. Here is how
it may be used in a simplified version of example 1.1 from the
Tk::UserGuide where a Button is set up to call a sub where the call to
get lies:

    #!/usr/bin/perl -w
    use strict;
    use Tk;

    my $main = MainWindow -> new();
    my $entry = $main -> Entry();
    $entry -> pack;
    $main->Button(-text => 'Print',
                  -command => sub{do_print($entry)}
                  )->pack;
    MainLoop;

    sub do_print {
        my ($widget) = @_;
        my $entered = $widget -> get();
        print "The string \"$entered\" was entered.\n";
    }

______________________________________________________________________



9.17. How do I hide a password Entry?

Set the -show option to zero, as in this example:

    $entry = $form->Entry(-textvariable => \$user_entry,
                          -show => 0);

______________________________________________________________________



9.18. How do I limit an Entry's insertion width?

Nick Ing-Simmons recommends writing a new Entry widget with the
insert method appropriately overridden by one that does limit the
width. His code is avaialable as a separate package from:

    http://w4.lns.cornell.edu/~pvhp/ptk/etc/LEntry-0_00.tar.gz

Now Brent Powers points out a possible problem with that approach and
recommends an insert() method as follows:

    Date: Thu, 22 Aug 1996 10:32:44 -0400
    From: "Brent B. Powers" <[email protected]>
    Subject: Re: How to set max characters for Entry widget
    In-reply-to: <199608211445.PAA09248@pluto>

    Ummm, before we set this into the distribution or FAQ, maybe we should
    make it work properly.  An example:  Imagine maxwidth configured to 8,
    the user fills in ABCDEFGH, moves the cursor back 4 places, and types
    I.  The SUPER::insert call sets the string to ABCDIEFGH, which this
    code then modifies to ABCDIEFG.

    Hmmm, how about

    sub insert {
      my($w, @args) = @_;
      my($max) = $w->cget(-maxwidth);
      my($sval) = $w->get;
      if (length($sval) >= $max) {
         $w->SUPER::insert(@args);
         if (length($w->get) > length($sval) {
        ## Reject it;
        my($idx) = $w->index('insert'); #  get current cursor position
            $w->delete(0, 'end');
            $w->insert(0, $sval);
            $w->icursor($idx);
        $w->bell;
      } else {
         $w->SUPER::insert(@args);
      }
    }

    Of course, that still doesn't deal with the selection, but ...

To which Nick Ing-Simmons responded (Thu Aug 22 1996):

    'paste' and <ButtonRelease-2> call insert method, what other selection
    issues are there?

______________________________________________________________________



9.19. How do I obtain Menus that do not tear off?

Nick Ing-Simmons outlined a couple of ways to achieve this result. The
critical feature being the -tearoff => 0 configuration option of the
Menu. In Nick's words:

    my $mb = $parent->Menubutton(...);    # The button
    my $menu = $mb->Menu(-tearoff => 0);  # Create a non-tearoff menu
    $mb->configure(-menu => $menu);       # Tell button to use it.
    $mb->command(....);

 Above is for clarity - you can loose $menu variable:

    my $mb = $parent->Menubutton(...);
    $mb->configure(-menu => $mb->Menu(-tearoff => 0));
    $mb->command(....);

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