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

# a list to get most of the standard graphic formats into a glob
my @exts = qw(wbmp wmf jpeg jpg bmp gif pcx png pnm pbm 
               pgm ppm tga targa xbm tiff tif xpm );
 
@exts = map { $_ = "*.$_" } @exts;   #map to setup the glob below
my @files = <@exts>; #non recursive
if(scalar @files == 0){ die "No photo files found\n" }
print "@files\n";


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

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

# start with base image
my $alpha =  0;
my $next = 0;
my $pb_base = Gtk2::Gdk::Pixbuf->new_from_file_at_scale ($files[0], 600,600,0);
my $pb_base_orig = $pb_base->copy();
#get next pixbuf
push (@files,shift(@files));  
my $pb_next = Gtk2::Gdk::Pixbuf->new_from_file_at_scale ($files[0], 600,600,0);

my $image = Gtk2::Image->new_from_pixbuf ($pb_base);
$vp->add($image);
$mw->set_title("fade demo");
$mw->show_all();

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

Gtk2->main;

sub sequence{

   if( $next ){
      # set base to be the previous next
      $pb_base = $pb_next;
      $pb_base_orig = $pb_base->copy();
      $image->set_from_pixbuf ($pb_base);
      Gtk2->main_iteration while Gtk2->events_pending;
      
      #get next pixbuf
      push (@files,shift(@files));  
      $pb_next = Gtk2::Gdk::Pixbuf->new_from_file_at_scale ($files[0], 600,600,0);
      $next = 0;
      $alpha = 0;

    }else{
    
    $alpha += 5;
    print "$alpha\n"; 
    if ($alpha == 255){ $next = 1; }  
    
   #$pixbuf1->composite ($pixbuf, $dest_x, $dest_y, $dest_width, $dest_height,
    #       $offset_x, $offset_y, $scale_x, $scale_y, $interp_type, $overall_alpha)

    $pb_next->composite ($pb_base, 0, 0, 600, 600,
           0, 0, 1, 1, 'nearest', $alpha);  # 0 <= alpha <= 255
    
    $image->set_from_pixbuf ($pb_base);
}

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