File Coverage

blib/lib/Time/Slideshow.pm

Criterion	Covered	Total	%
statement	53	58	91.3
branch	5	8	62.5
condition	7	11	63.6
subroutine	12	14	85.7
pod	10	11	90.9
total	87	102	85.2

package Time::Slideshow;
use strict;
use Time::HiRes qw(time);
use vars qw($VERSION);
$VERSION= '0.02';

=head1 NAME

Time::Slideshow - simple stateless slideshow with a fixed set of images

=head1 SYNOPSIS

    my $slideshow= Time::Slideshow->new(
        starttime => 0,
        slides => [ 'picture1.jpg', 'picture2.jpg' ],
        shuffle => 0, # pseudo-rng
        duration => 45, # show each slide for 45 seconds
    );
    my $current_slide= $slideshow->current_slide;           # picture1.jpg
    my $next_slide= $slideshow->next_slide;                 # picture2.jpg
    sleep $slideshow->seconds_to_next_slide;

=head1 OVERVIEW

This module abstracts the inner workings of a slideshow, selecting the
next slide to display and calculating the time until the next picture. It
is possible to use this object in an asynchronous manner across machines
as the complete slide sequence is precalculated from the wallclock time.

The module has no methods to advance the slideshow forwards or backwards
other than through the passage of time.

=head1 METHODS

=head2 C<< Time::Slideshow->new %options >>

  my $slideshow= Time::Slideshow->new(
      slides => [ glob '~/backgrounds/*.jpg' ],
      duration => 300, # five minutes per image
      shuffle => 1, # permute the order of images
  )

Creates a new slideshow object and returns it. The options are

=over 4

=item B

Array reference to the slides. These can be filenames
or URLs or whatever else helps your program to find and display
the appropriate image.

=item B

The time how long every image is displayed, in seconds. The default
value is 45.

=item B

If you want the order of the images to be shuffled, pass
a true value to this option. See the below discussion
on what different orders you can expect from shuffling.

=item B

If you want to set up a different offset of the start time,
pass this option with the epoch value of the start time. Usually,
you want to leave this parameter at its default of 0.

=back

=cut

sub new {
    my( $class, %options )= @_;
    $options{ starttime }||= 0;
    $options{ shuffle }||= 0;
    $options{ duration }||= 45;
    $options{ slides }||= [];

    my $self= bless \%options, $class;

    $self
}

sub starttime { $_[0]->{ starttime }};
sub duration { $_[0]->{ duration }};
sub slides { $_[0]->{ slides }};

=head2 C<< $show->add_slide( @slides ) >>

  $show->add_slide( glob '~/new_backgrounds/*' );

If you want to add slides after object
creation, you can use this method.

=cut

sub add_slide {
    my( $self, @slides )= @_;
    push @{ $self->slides }, @slides
};

=head2 C<< $show->current_slide >>

  print "Now displaying ", $show->current_slide, "\n";

Returns the name of the slide that is currently displayed.

This method is the central method for your application to
get the filename or URL of the image that your application
needs to display.

=cut

sub current_slide {
    my( $self, $time )= @_;
    $self->slide_at( $self->current_slide_index( $time ))
}

=head2 C<< $show->next_slide >>

  print "Next up is ", $show->next_slide, "\n";

Returns the name of the slide that will be displayed after the
current slide.

You can use this method to preload the image data
for the upcoming slide.

=cut

sub next_slide {
    my( $self, $time )= @_;
    $self->slide_at( $self->current_slide_index( $time ) +1 )
}

=head2 C<< $show->seconds_to_next_slide >>

  my $wait= $show->seconds_to_next_slide;
  sleep $wait;

Returns the time remaining to the next slide
transition.

You can use this method to pause your program or perform
other tasks until the next image
needs to be displayed.

=cut

sub seconds_to_next_slide {
    my( $self, $time )= @_;
    if( ! defined $time ) {
        $time= Time::HiRes::time;
    };
    $time -= $self->{ starttime };
    #warn sprintf "At %d, window %d, in %d", $time, $self->duration, $self->duration - ($time % $self->duration);
    $self->duration - ($time % $self->duration)
};

=head2 C<< $show->current_slide_index >>

  my $current_slide_index= $show->current_slide_index;

This returns the index of the slide that is currently displayed.

Most likely, you want to use C<< $show->current_slide >> instead.

=cut

sub current_slide_index {
    my( $self, $time )= @_;
    $time = time
        unless defined $time;
    $time -= $self->{ starttime };

    my $items= 0+@{ $self->slides };
    return undef unless $items;

    my $index= int (($time % ($self->duration * $items)) / $self->duration);

    if( $self->{ shuffle } and $items > 1) {
        # Apply a permutation
        # We don't want permutation 0 and 1 as 0 and 1 are identical
        # Step is the distance between items
        # Incr is the shift we need to apply per round
        #           0 1 2 3 4 5
        # Shuffle 1: Step = 2
        #           0   1   2
        #             3   4   5
        # Shuffle 2: Step = 3
        #           0     1
        #             2     3
        #               4     5
        #
        # For 10 items, Permutation 8 (Step size 3)
        #           0 1 2 3 4 5 6 7 8 9
        #           0     1     2     3
        #             4     5     6
        #               7     8     9

        my $permutation= (int ($time / ($self->duration * $items)) % ($items-2));
        my $step= $permutation;
        $step++; # Increment between 1 and $items-1

        my $gcd= gcd( $items, $step );
        my $round_size= int( $items / $gcd );

        # The round counts from $round_size towards 1 to shuffle the order of loops a bit
        my $round= $round_size - int($index / $round_size) +1;

        my $old_index= $index;
        $index= ((($old_index *$step) % $items) + $round ) % $items;

        #warn sprintf "Old Index % 2d  Step: % 2d  Round: % 2d  Round size: % 2d  Index: % 2d  GCD: % 2d\n",
        #              $old_index,     $step,      $round,      $round_size,      $index,      $gcd;
    };

    $index
};

=head2 C<< $show->slide_at $index >>

    my $slide_count= @{ $show->slides };
    for my $slide ( 0..$slide_count-1 ) {
        print "Slide $slide: ", $show->slide_at( $slide ), "\n";
    };

Returns the name of the slide at the given index.

=cut

sub slide_at {
    my( $self, $index )= @_;
    $index %= 0+@{ $self->slides };
    $self->slides->[ $index ]
}

# Some math utilities to find the gcd, for the "random" shuffles
sub gcd {
    my( $gcd )= shift;
    for my $d ( @_ ) {
        my $div= $d;
        while( $div ) {
            ($gcd, $div) = ($div, $gcd % $div);
        };
    };
    $gcd
}

1;

__END__