package Font::TTF::Delta;

=head1 NAME 

Font::TTF::Delta - Opentype Device tables

=head1 DESCRIPTION

Each device table corresponds to a set of deltas for a particular point over
a range of ppem values.

=over 

=item first

The first ppem value in the range

=item last

The last ppem value in the range

=item val

This is an array of deltas corresponding to each ppem in the range between
first and last inclusive.

=item fmt

This is the fmt used (log2 of number bits per value) when the device table was
read. It is recalculated on output.

=back 

=head1 METHODS

=cut

use strict;
use Font::TTF::Utils;

=head2 new

Creates a new device table

=cut

sub new
{
    my ($class) = @_;
    my ($self) = {};

    bless $self, $class;
}


=head2 read

Reads a device table from the given IO object at the current location

=cut

sub read
{
    my ($self, $fh) = @_;
    my ($dat, $fmt, $num, $i, $j, $mask);

    $fh->read($dat, 6);
    ($self->{'first'}, $self->{'last'}, $fmt) = TTF_Unpack("S3", $dat);
    $self->{'fmt'} = $fmt;

    $fmt = 1 << $fmt;
    $num = ((($self->{'last'} - $self->{'first'} + 1) * $fmt) + 15) >> 8;
    $fh->read($dat, $num);

    $mask = (0xffff << (16 - $fmt)) & 0xffff;
    $j = 0;
    for ($i = $self->{'first'}; $i <= $self->{'last'}; $i++)
    {
        if ($j == 0)
        {
            $num = TTF_Unpack("S", substr($dat, 0, 2));
            substr($dat, 0, 2) = '';
        }
        push (@{$self->{'val'}}, ($num & $mask) >> (16 - $fmt));
        $num <<= $fmt;
        $j += $fmt;
        $j = 0 if ($j >= 16);
    }
    $self;
}


=head2 out($fh, $style)

Outputs a device table to the given IO object at the current location, or just
returns the data to be output if $style != 0

=cut

sub out
{
    my ($self, $fh, $style) = @_;
    my ($dat, $fmt, $num, $mask, $j, $f, $out);

    foreach $f (@{$self->{'val'}})
    {
        my ($tfmt) = $f > 0 ? $f + 1 : -$f;
        $fmt = $tfmt if $tfmt > $fmt;
    }

    if ($fmt > 8)
    { $fmt = 3; }
    elsif ($fmt > 2)
    { $fmt = 2; }
    else
    { $fmt = 1; }

    $out = TTF_Pack("S3", $self->{'first'}, $self->{'last'}, $fmt);

    $fmt = 1 << $fmt;
    $mask = 0xffff >> (16 - $fmt);
    $j = 0; $dat = 0;
    foreach $f (@{$self->{'val'}})
    {
        $dat |= ($f & $mask) << (16 - $fmt - $j);
        $j += $fmt;
        if ($j >= 16)
        {
            $j = 0;
            $out .= TTF_Pack("S", $dat);
            $dat = 0;
        }
    }
    $out .= pack('n', $dat) if ($j > 0);
    $fh->print($out) unless $style;
    $out;
}

=head2 $d->signature()

Returns a content based identifying string for this delta for
compression purposes

=cut

sub signature
{
    my ($self) = @_;
    return join (",", $self->{'first'}, $self->{'last'}, @{$self->{'val'}});
}


=head2 $d->out_xml($context)

Outputs a delta in XML

=cut

sub out_xml
{
    my ($self, $context, $depth) = @_;
    my ($fh) = $context->{'fh'};

    $fh->printf("%s<delta first='%s' last='%s'>\n", $depth, $self->{'first'}, $self->{'last'});
    $fh->print("$depth$context->{'indent'}" . join (' ', @{$self->{'val'}}) . "\n") if defined ($self->{'val'});
    $fh->print("$depth</delta>\n");
}

1;

=head1 AUTHOR

Martin Hosken L<Martin_Hosken@sil.org>. 


=head1 LICENSING

Copyright (c) 1998-2013, SIL International (http://www.sil.org) 

This module is released under the terms of the Artistic License 2.0. 
For details, see the full text of the license in the file LICENSE.

The test suite contains test fonts released under the SIL Open Font License 1.1, see OFL.txt.

=cut