#!/usr/bin/perl
use strict;
use warnings;
use Gtk2 '-init';
use LWP::Simple;


# cheap webget, no error reporting
if( ! -e 'earth.jpg' and ! -e 'moon.jpg'){

   print "downloading test images, please wait\n";
     foreach my $localfile('earth.jpg','moon.jpg'){
     mirror( "http://zentara.net/$localfile", $localfile );
  }
}


my $mw = Gtk2::Window->new;
$mw->signal_connect('destroy', sub { Gtk2->main_quit });

my $vp = Gtk2::Viewport->new(undef, undef);
$mw->add($vp);

my $pixbuf = Gtk2::Gdk::Pixbuf->new_from_file_at_scale ('earth.jpg', 600,600,0);
my $pixbufa = $pixbuf->copy();
#my ($x, $y) = ($pixbufa->get_width, $pixbufa->get_height);
#print "$x $y\n";
my $pixbuf1 = Gtk2::Gdk::Pixbuf->new_from_file_at_scale ('moon.jpg', 600,600,0);
my $pixbufb = $pixbuf1->copy();
#my ($x1, $y1) = ($pixbufb->get_width, $pixbufb->get_height);
#print "$x1 $y1\n";

#$pixbuf1->composite ($pixbuf, $dest_x, $dest_y, $dest_width, $dest_height,
#       $offset_x, $offset_y, $scale_x, $scale_y, $interp_type, $overall_alpha)

# start with base image
my $toggle = 5;
my $alpha =  0;
$pixbufb->composite ($pixbufa, 0, 0, 600, 600,
       0, 0, 1, 1, 'nearest', $alpha);  # 0 <= alpha <= 255

my $image = Gtk2::Image->new_from_pixbuf ($pixbufa);
$vp->add($image);

$mw->set_title("fade demo");
$mw->show_all();

my $id = Glib::Timeout->add (100, \&sequence);

Gtk2->main;

sub sequence{
   
     $alpha += $toggle;
     print "$alpha\n"; 
     if ($alpha == 255){ $toggle = -5 }  
     if ($alpha == 0){ $toggle = 5 }  
   
    $pixbufb->composite ($pixbufa, 0, 0, 600, 600,
           0, 0, 1, 1, 'nearest', $alpha);  # 0 <= alpha <= 255
    
    $image->set_from_pixbuf ($pixbufa);

    Gtk2->main_iteration while Gtk2->events_pending;
    
    # prevents accumulation of pixbuf changes
    $pixbufa = $pixbuf->copy(); 
     
 return 1;
}