#!/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_height, $y+$ypad+$item_height,
          -width   => '1m',
          -outline => '#aaaaff',
          -fill    => '#6666aa',
          -tags    => "item$i"
          );
    } else {
      $canv->coords("item$i", $x+$xpad, $y+$ypad, $x+$xpad+$item_height, $y+$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;