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Command Line Arguemnts and Resources

See manpage for module   Tk::CmdLine

Command line arguments are automatcially extracted from the ARGV array
when you either call             Tk::CmdLine::SetArguments()
OR you create the main window    $wm=MainWindow->new();

As such you should create you main window (or SetArguments) BEFORE you parse
the ARGV array for your program specific arguments.

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Extra Data associated with a widget

Perl/Tk widgets are represented as references to hashes.
You can store whatever you like in the hash. Names starting and ending 
with _ e.g. $widget->{_MINE_} are reserved for core (though I am lax 
about that).

There is also a hook : 

my $hash = $widget->privateData();          # key is caller's package name
my $hash = $widget->privateData('MyKey');   # explcit key

Which will return a sub-hash which is "your very own".

Nick Ing-Simmons <nik@tiuk.ti.com>

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Multiple Listboxes - only one item in any of them selected

By default Listbox has -exportselection => 1 so Listbox's selection is 
also the X 'PRIMARY' selection - X mandates that only one window can own
an X selection at a time. So when one Listbox asserts it the other one
looses it.

The fix is to turn off -exportselection on one or both of the listboxes.

Presumably the exportselection works slightly
differently if multiple selection listboxes are being used.

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Text/Entry widget callback on Enter

Use a bind with..

	$input_widget->bind("<Return>" => sub { ... });

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Scrolled Canvas:  Problem with raise() and lower().

When using the scrolled method to create a canvas, it seems as if the
$canvas->raise(); and $canvas->lower(); commands are trying to raise the
$canvas as a "window" rather than raise or lower the actual canvas object's
within the window.

The problem is that Scrolled returns the pointer for the frame containing the
canvas widget, and not the widget itself. And unknown or extra methods are
however ``Delegates()'' to the contained sub-widget.

When you create a Canvas with Scrolled, you have to ask for the Canvas using
Subwidget(). to use raise and lower on the objects and not the frame window.

Example Solution...
   my $frame=$top->Scrolled('Canvas', -scrollbars=>'se',
	                              -scrollregion=>\@scrollregion);
   my $canvas=$frame->Subwidget('canvas');

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Resizing a Font on the fly

    use Tk;
    use Tk::Font;

    $top = new MainWindow;

    $f = $top->fontCreate(-size => 20, -family => "helvetica");

    $c=$top->Canvas->pack;
    $c->createText(100,50,-text => "bla blubber", -font => $f);
    $c->createText(30,150,-text => "foo bar", -font => $f);

    $top->Button(-text => "Smaller",
		-command => sub {
		    $f->configure(-size => $f->actual(-size)-1);
		})->pack;
    MainLoop;

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Adding a Method to an Existing Widget

The "clean way" - create a subclass:

  package Tk::MyWhatever;
  use base qw(Tk::Whatever);

  Construct Tk::Widget 'MyWhatever';   # you could clobber 'Whatever' too

  sub new_method {
    ...
  }

  1;
  __END__


The easy way :

  use Tk::Whatever (); # make sure module is loaded.

  sub Tk::Whatever::new_method {
  ...
  }

The above is a little tricky in a way that may not be an issue to you:
the _body_ of the sub is executed in the enclosing "package" rather 
than Tk::Whatever.

If that does matter then do it this way instead:

  use Tk::Whatever ();
  { package Tk::Whatever;
    sub new_method {
      ...
    }
  }

Note that in none of these cases can "new_method" see any "my" variables in 
Tk/Whatever.pm - it will see the "my" variables in file it is in 
(which is what lexical scoping is all about) which can be handy.

As far as I know all Tk core classes which have global 'my' variables
(e.g. MainWindow's list of windows) have access methods to get at them.

Nick Ing-Simmons 

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Speeding up Complex Canus Draws

A possible solution: packForget the canvas while drawing the lines
onto the canvas, and the re-pack() the canvas again. For speeding up
drawing lines: try to draw as many as possible line segments with one
createLine()-call. It's significantly faster. If you like, you can
also use the Tk API functions to draw lines in an XS module. This will
be about 2-3x faster.

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Drawing Dotted lines on a Canvas

Does anyone know how to make dotted lines on a canvas?  (not a bunch of
little lines)

The following works fine for X Windows but failed for Win95
 
use Tk;

$mw = new MainWindow(-name => 'test', -title => 'test');
$can = $mw->Canvas;
$can->pack(-fill => both, -expand => yes);

$gridsize = 20;

 # Create the dots bitmap
 my (@bits);
 for (my $i = 0; $i < $gridsize; $i++) {
   if ($i == 0) {
     $bits[$i] = "1";
   } else {
     $bits[$i] = ".";
   }
 }

 print @bits;
 push @bitmaps, pack('b8' x $gridsize, @bits);
 $mw->DefineBitmap('dots' => 8, $gridsize, $bitmaps[-1]);

 $can->create('line', 30, 0, 30, 300, -stipple => 'dots', -width => 8);

MainLoop;

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Build Hint

Nick Ing-Simmons <nick@ing-simmons.net> writes:
>Tim Evans <tkevans@eplrx7.es.dupont.com> writes:
>>I've been trying to install Tk400.202 on a Solaris 7 (i.e., 2.7), 
>>with perl 5.005_57.  I get numerous undefined's referencing 'sv_undef'
>>and also 'sv_arenaroot'.
>
>If you are brave enough to use 5.005_57 the you should consider Tk800.014.
>
>But that said - read the 5.005_57 docs - you need to set the "POLLUTE" 
>option so that 5.005_57 fills the name space with lots of #defines
>the way 5.000 .. 5.004 did.
>
>IRRC 
>
>perl Makefile.PL POLLUTE=1

That is not quite sufficent - Tk400.* is a little too intimate with 
perls "magic" vtables (which even POLLUTE does not #define back to 
old style): 

So you also need this 3-char tweak:

--- /tmp/Tk400.202/tkGlue.c%	Fri Jul 16 09:47:26 1999
+++ /tmp/Tk400.202/tkGlue.c	Fri Jul 16 09:47:26 1999
@@ -2694,7 +2694,7 @@
  mg->mg_obj = 0;
  mg->mg_type = 'U';
  mg->mg_len = 0;
- mg->mg_virtual = &vtbl_uvar;
+ mg->mg_virtual = &PL_vtbl_uvar;
 
  mg_magical(sv);
  New(666, ufp, 1, struct ufuncs);



Then it builds for me with gcc-2.8.1, perl5.005_57, solaris7.

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