Well that information is earlier in the script, where the sub is called. If you look at the widget demo, for plot, you should be able to see where it's called. However, I have to agree that the demos are written by people who are good, and take alot of "code shortcuts" which are hard for beginners to see.

So rather than try to explain to you, what you can find yourself, I will give a "more straight-forward" example.

Like in kvale's first reply, you need to specify the "boundaries" of what you want to capture as postscript. That is what the $pinfo is for. So look at this simple example.

#!/usr/bin/perl
use Tk;
#to change the background color, edit the ps file 
#  0.000 0.000 0.000 setrgbcolor AdjustColor 
#  fill 

$width = 800;
$height = 500;
my $main = MainWindow->new();
my $canvas = $main->Canvas( -width=>$width, -height=>$height, -backgro
+und=>"black");
$canvas->pack( -expand=>1,-fill=>'both');

&create;

$canvas->update;
$main->update;

$main->Button(
    -text    => "Save",
    -command => [sub {
         $canvas->update;
         my @capture=();
         my ($x0,$y0,$x1,$y1)=$canvas->bbox('all');
         @capture=('-x'=>$x0,'-y'=>$y0,-height=>$y1-$y0,-width=>$x1-$x
+0);
         $canvas -> postscript(-colormode=>'color',
                               -file=>$0.'.ps',
                               -rotate=>0,
                               -width=>800,
                               -height=>500,
                               @capture);

                              }

  ]  )->pack;

MainLoop;

sub create{
$canvas->createOval(100, 100, 600, 600,-fill=>'green')

}
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