#!/usr/bin/perl

use strict;
use warnings;

use Glib qw/TRUE FALSE/;
use Gtk2 '-init';

use Gnome2::Canvas;
use constant PI => 3.1415926;
use Tie::Watch;

my $width  = 200;
my $height = 100;
my $value  = 0;
my $max = 100;
my $min = 0; 

my $watch = Tie::Watch->new(
    -variable => \$value,
    -shadow   => 0,
    -store    => \&update_meter,
);

my $window = Gtk2::Window->new;
$window->signal_connect( 'delete-event' => \&delete_event );
$window->set_default_size( $width, $height );

my $canvas = Gnome2::Canvas->new_aa();
$canvas->set_scroll_region( 0, 0, $width, $height );   #to get upper left corner
$canvas->set_size_request( $width, $height );   #useless?
$window->add($canvas);
$window->show_all;

my $root = $canvas->root();

my $text = Gnome2::Canvas::Item->new(
    $root, 'Gnome2::Canvas::Text',
    x          => $width / 2,
    y          => $height * .50,
    fill_color => 'yellow',
    font       => 'Sans 14',
    anchor     => 'GTK_ANCHOR_CENTER',
    text       => $value
);

my $box = Gnome2::Canvas::Item->new(
    $root, 'Gnome2::Canvas::Rect',
    x1            => 0,
    y1            => 0,
    x2            => $width,
    y2            => $height,
    fill_color    => 'black',
    outline_color => 'black'
);

my $hub = Gnome2::Canvas::Item->new(
    $root, "Gnome2::Canvas::Ellipse",
    x1            => $width / 2 - 8,
    y1            => ( $height * .80 ) - 8,
    x2            => $width / 2 + 8,
    y2            => ( $height * .80 ) + 8,
    fill_color    => 'white',
    outline_color => 'black'
);

my $gauge = Gnome2::Canvas::Item->new(
    $root,
    'Gnome2::Canvas::Bpath',
    outline_color => 'white',
    fill_color    => 'steelblue',
);

$gauge->set_path_def( semi_circle_path() );

my $floor = Gnome2::Canvas::Item->new(
    $root, 'Gnome2::Canvas::Rect',
    x1            => 0,
    y1            => $height * .80,
    x2            => $width,
    y2            => $height,
    fill_color    => 'black',
);

my $needle = Gnome2::Canvas::Item->new(
    $root, "Gnome2::Canvas::Line",
    points => [ $width / 2, ( $height * .80 ), $width / 2, 10 ],
    width_units    => 5,
    fill_color     => 'hotpink',
    last_arrowhead => 1,
    arrow_shape_b  => 20
);


$box->lower_to_bottom;
$needle->raise_to_top;
$hub->raise_to_top;
$text->raise($gauge);

my $toggle = 1;
my $count = 0;
Glib::Timeout->add (50, 
                 sub { 
                    $count += $toggle; 
                    $value = $count;
                    return TRUE;
                  }
        );

Gtk2->main;
###########################################################3
sub delete_event {
    $watch->Unwatch;
#    $canvas->destroy;
    Gtk2->main_quit;
    return 1;
}
###########################################################3
sub update_meter {

    if ( $value <= $min )   { $toggle = 1 }
    if ( $value >= $max ) { $toggle = -1 }
    my $pos = $value * PI/$max;

    my $x   = $width/2      -  $height * .80 * ( cos( $pos ) );
    my $y   = $height * .80 -  $height * .80 * ( sin( $pos ) )  ;

   $needle->set( points => [ $width / 2, ( $height * .80 ), $x, $y ], );
   $text->set(text => $value);   #causes error message on exit
   return $value;
}

sub semi_circle_path {
    my $p = Gnome2::Canvas::PathDef->new;
    $p->moveto(180, 80);
    $p->lineto(20, 80);
    $p->curveto(
      20, -26,
      180, -26,
      180, 80
    );
    $p->closepath;

    return $p;
}