Ookey I have found the mistake. To summarize, binding of 'Configure' event on canvas didn't work and vertical scrollbar wasn't displayed. The reason is the little exception in Canvas API according to which I can't call canvas binding as usual like

$canv->bind(...);
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According to http://search.cpan.org/dist/Tk/pod/bind.pod#CAVEATS:

" Note that for the Canvas widget, the call to bind has to be fully qualified. This is because there is already a bind method for the Canvas widget, which binds individual canvas tags. $canvas->Tk::bind "

After fixing everything works fine.

Here is a fixed script:

#!/usr/bin/env perl

use Tk;
use strict;
use POSIX;

my $draw_items = 1;

sub update_fileview {
  scroll_off();
  hscroll_off();

  our $canv;
  our $vscroll;
  our $hscroll;
  our $item_height;

  my $num_items = 2000;

  my $canv_width = $canv->width;
  my $canv_height = $canv->height;

  my $canv_width2 = $canv_width - $vscroll->width;
  
  my $canv_scroll_width = $canv_width2;

  my $xpad = $item_height / 20;
  my $ypad = $item_height / 20;
  my $item_box_height = $item_height + $ypad * 2;
  my $item_box_width = $item_height + $xpad * 2;

  my $nitems_in_row = $canv_width2 / $item_box_width;

  if ($nitems_in_row < 1) {
    $nitems_in_row = 1;
    if ($item_box_width > $canv_width2) {
      $canv_scroll_width = $item_box_width + $xpad + $vscroll->width;
      hscroll_on();
    }
  }

  my $num_rows = ceil("$num_items.0" / "$nitems_in_row.0");
  my $canv_scroll_height = $num_rows * $item_box_height;

  if ($canv_scroll_height > $canv_height) {
    scroll_on();
    $canv->configure(-scrollregion => [0, 0, $canv_scroll_width, $canv
+_scroll_height] );
  } else {
    $canv->configure(-scrollregion => [0, 0, $canv_scroll_width, $canv
+_height] );
  }

  my $i = my $r = my $c = 0;

  for (; $i < $num_items; $i++) {
    our $y = $r * $item_box_height;
    our $x = $c * $item_box_width;

    if ($x + $item_box_width + $xpad > $canv_width2) {
      $r++;
      if ($c != 0) {
        $c = 0;
        $y = $r * $item_box_height;
        $x = $c * $item_box_width;
        $c++;
      }
    } else {
      $c++;
    }

    if ($y + $item_box_height + $ypad > $canv_height) {
      scroll_on();
    }
    if ($draw_items) {
      $canv->create('rectangle', $x+$xpad, $y+$ypad, $x+$xpad+$item_he
+ight, $y+$ypad+$item_height,
          -width   => '1m',
          -outline => '#aaaaff',
          -fill    => '#6666aa',
          -tags    => "item$i"
          );
    } else {
      $canv->coords("item$i", $x+$xpad, $y+$ypad, $x+$xpad+$item_heigh
+t, $y+$ypad+$item_height);
    }
  }

  $draw_items = 0;
}

sub scroll_on {
  our $vscroll;
  $vscroll->raise();
}

sub scroll_off {
  our $vscroll;
  $vscroll->lower();
}

sub hscroll_on {
  our $hscroll;
  $hscroll->grid();
}

sub hscroll_off {
  our $hscroll;
  $hscroll->gridRemove();
}


our $top = new MainWindow;
our $canv = $top->Canvas(-background => "blue");
our $vscroll = $top->Scrollbar(-command => ['yview', $canv]);
our $hscroll = $top->Scrollbar(
    -command => ['xview', $canv],
    -orient  => 'horizontal');
$canv->configure(
    -yscrollcommand => ['set', $vscroll],
    -xscrollcommand => ['set', $hscroll]);

$canv->grid(
    -row    => 0,
    -column => 0,
    -sticky => 'nsew');
$vscroll->grid(
    -row    => 0,
    -column => 0,
    -sticky => 'nse');
$hscroll->grid(
    -row    => 1,
    -column => 0,
    -sticky => 'we');
$top->gridRowconfigure( 0, -weight => 1);
$top->gridColumnconfigure(0, -weight => 1);
$top->gridRowconfigure(1, -weight => 0);
$vscroll->lower();
$canv->Tk::bind('<Configure>' => sub {
    update_fileview();
});

our $screen_height = $top->screenheight;
our $item_height = $screen_height / 10;
our $min_item_offset = $item_height / 10;

our $top_height = $screen_height / 2;
our $top_width = ($top_height * 4) / 3;
$top->geometry("=${top_width}x$top_height");

$canv->Tk::bind('<Button-1>', sub { scroll_on() });
$canv->Tk::bind('<Button-3>', sub { scroll_off() });

MainLoop;
[download]