#! /usr/bin/env perl

=begin COPYRIGHT

----------------------------------------------------------------------------

    Copyright (C) 2005-2021 Marc Penninga.

    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License
    as published by the Free Software Foundation, either version 2
    of the License, or (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to
        Free Software Foundation, Inc.,
        59 Temple Place,
        Suite 330,
        Boston, MA 02111-1307,
        USA

----------------------------------------------------------------------------

=end COPYRIGHT

=cut

use strict;
use warnings;

use integer;
use Getopt::Long ();
use List::Util @List::Util::EXPORT_OK;
use Pod::Usage;

my $VERSION = "20211115";

our ($NUM_GLYPHS, $UNITS_PER_EM, %kern);

sub main {
    %ARGV = (
        print_func  =>  \&print_kpx,
    );

    Getopt::Long::GetOptions(
        'help|?'    =>  sub { pod2usage(-verbose => 0) },
        'version'   =>  sub { print "$VERSION\n"; exit },
        'doc'       =>  sub { pod2usage(-verbose => 2) },
        'afm'       =>  sub { $ARGV{print_func} = \&print_kpx },
        'kpx'       =>  sub { $ARGV{print_func} = \&print_kpx },
        'lua'       =>  sub { $ARGV{print_func} = \&print_lua },
    ) or pod2usage(-verbose => 0);
    pod2usage(-verbose => 0) if @ARGV != 1;

    my %font = OTF::get_tables($ARGV[0]);

    $NUM_GLYPHS = unpack '@4n', $font{maxp};
    $UNITS_PER_EM = unpack '@18n', $font{head};

    my @glyph_name = map { sprintf "index%d", $_ } 0 .. $NUM_GLYPHS - 1;
    if (defined $font{CFF}) {
        OTF::CFF::get_glyph_names($font{CFF}, \@glyph_name);
    }

    if (defined $font{kern}) {
        OTF::Kern::parse_kerntable($font{kern});
    }

    if (defined $font{GPOS}) {
        my @lookup_list_indices
            = OTF::GPOS::get_lookup_list_indices($font{GPOS});
        my @all_lookups = OTF::GPOS::get_lookups($font{GPOS});
        my @lookups = @all_lookups[@lookup_list_indices];
        my @subtables = map { OTF::GPOS::get_subtables($_) } @lookups;

        for my $subtable (@subtables) {
            my $pos_format = unpack 'n', $subtable;
            if ($pos_format == 1) {
                OTF::GPOS::parse_pos_format_1($subtable);
            }
            elsif ($pos_format == 2) {
                OTF::GPOS::parse_pos_format_2($subtable);
            }
            else {
                warn "[ERROR] invalid PosFormat $pos_format ignored";
            }
        }
    }

    &{$ARGV{print_func}}( \%kern, \@glyph_name );
    return;
}

# ------------------------------------------------------------------------
# Print kerning data in Adobe's KPX format
# ------------------------------------------------------------------------
sub print_kpx {
    my %kern = %{ shift @_ };
    my @glyph = @{ shift @_ };

    my $num_kernpairs = sum map { scalar keys %{$kern{$_}} } keys %kern;
    print "StartKernData\nStartKernPairs $num_kernpairs\n";
    for my $l (sort { $glyph[$a] cmp $glyph[$b] } keys %kern) {
        my $l_glyph = $glyph[$l];
        for my $r (sort { $glyph[$a] cmp $glyph[$b] } keys %{$kern{$l}}) {
            print "KPX $l_glyph $glyph[$r] ",
                  "$kern{$l}{$r}\n";
        }
    }
    print "EndKernPairs\nEndKernData\n";
}

# ------------------------------------------------------------------------
# Print kerning data as a Luatex custom font feature
# ------------------------------------------------------------------------
sub print_lua {
    my %kern = %{ shift @_ };
    my @glyph = @{ shift @_ };

    print <<'END_FEATURE_PREFIX';
fonts.handlers.otf.addfeature {
    name = 'kern',
    type = 'kern',
    data = {
END_FEATURE_PREFIX

    for my $l ( sort { $glyph[$a] cmp $glyph[$b] } keys %kern ) {
        print ' ' x 8, "[ '$glyph[$l]' ] = {";
        for my $r ( sort { $glyph[$a] cmp $glyph[$b] } keys %{$kern{$l}} ) {
            print "\n", ' ' x 12, "[ '$glyph[$r]' ] = $kern{$l}{$r},";
        }
        print " },\n";
    }

    print <<'END_FEATURE_POSTFIX';
    }
}
END_FEATURE_POSTFIX
}

########################################################################


package OTF;

#-----------------------------------------------------------------------
# Return a hash with all tables (as strings) from the font
#-----------------------------------------------------------------------
sub get_tables {
    my $filename = shift;

    open my $fontfile, '<:raw', $filename
        or die "[ERROR] can't open $filename: $!";
    my $fontdata = do { local $/; <$fontfile> };
    close $fontfile;

    my ($sfnt_version, @tables) = unpack 'a4nx6/(a16)', $fontdata;

    die "[ERROR] $filename: unknown font type"
        unless $sfnt_version eq "\x00\x01\x00\x00"
            || $sfnt_version eq 'OTTO';

    my %table = map { my ($tag, $offset, $length) = unpack 'A4@8N@12N', $_;
                      ($tag => substr $fontdata, $offset, $length);
                    }
                    @tables;

    return %table;
}


########################################################################


package OTF::CFF;

my @STANDARD_STRINGS = qw(
    .notdef space exclam quotedbl
    numbersign dollar percent ampersand
    quoteright parenleft parenright asterisk
    plus comma hyphen period

    slash zero one two
    three four five six
    seven eight nine colon
    semicolon less equal greater

    question at A B
    C D E F
    G H I J
    K L M N

    O P Q R
    S T U V
    W X Y Z
    bracketleft backslash bracketright asciicircum

    underscore quoteleft a b
    c d e f
    g h i j
    k l m n

    o p q r
    s t u v
    w x y z
    braceleft bar braceright asciitilde

    exclamdown cent sterling fraction
    yen florin section currency
    quotesingle quotedblleft guillemotleft guilsinglleft
    guilsinglright fi fl endash

    dagger daggerdbl periodcentered paragraph
    bullet quotesinglbase quotedblbase quotedblright
    guillemotright ellipsis perthousand questiondown
    grave acute circumflex tilde

    macron breve dotaccent dieresis
    ring cedilla hungarumlaut ogonek
    caron emdash AE ordfeminine
    Lslash Oslash OE ordmasculine

    ae dotlessi lslash oslash
    oe germandbls onesuperior logicalnot
    mu trademark Eth onehalf
    plusminus Thorn onequarter divide

    brokenbar degree thorn threequarters
    twosuperior registered minus eth
    multiply threesuperior copyright Aacute
    Acircumflex Adieresis Agrave Aring

    Atilde Ccedilla Eacute Ecircumflex
    Edieresis Egrave Iacute Icircumflex
    Idieresis Igrave Ntilde Oacute
    Ocircumflex Odieresis Ograve Otilde

    Scaron Uacute Ucircumflex Udieresis
    Ugrave Yacute Ydieresis Zcaron
    aacute acircumflex adieresis agrave
    aring atilde ccedilla eacute

    ecircumflex edieresis egrave iacute
    icircumflex idieresis igrave ntilde
    oacute ocircumflex odieresis ograve
    otilde scaron uacute ucircumflex

    udieresis ugrave yacute ydieresis
    zcaron exclamsmall Hungarumlautsmall dollaroldstyle
    dollarsuperior ampersandsmall Acutesmall parenleftsuperior
    parenrightsuperior twodotenleader onedotenleader zerooldstyle

    oneoldstyle twooldstyle threeoldstyle fouroldstyle
    fiveoldstyle sixoldstyle sevenoldstyle eightoldstyle
    nineoldstyle commasuperior threequartersemdash periodsuperior
    questionsmall asuperior bsuperior centsuperior

    dsuperior esuperior isuperior lsuperior
    msuperior nsuperior osuperior rsuperior
    ssuperior tsuperior ff ffi
    ffl parenleftinferior parenrightinferior Circumflexsmall

    hyphensuperior Gravesmall Asmall Bsmall
    Csmall Dsmall Esmall Fsmall
    Gsmall Hsmall Ismall Jsmall
    Ksmall Lsmall Msmall Nsmall

    Osmall Psmall Qsmall Rsmall
    Ssmall Tsmall Usmall Vsmall
    Wsmall Xsmall Ysmall Zsmall
    colonmonetary onefitted rupiah Tildesmall

    exclamdownsmall centoldstyle Lslashsmall Scaronsmall
    Zcaronsmall Dieresissmall Brevesmall Caronsmall
    Dotaccentsmall Macronsmall figuredash hypheninferior
    Ogoneksmall Ringsmall Cedillasmall questiondownsmall

    oneeighth threeeighths fiveeighths seveneighths
    onethird twothirds zerosuperior foursuperior
    fivesuperior sixsuperior sevensuperior eightsuperior
    ninesuperior zeroinferior oneinferior twoinferior

    threeinferior fourinferior fiveinferior sixinferior
    seveninferior eightinferior nineinferior centinferior
    dollarinferior periodinferior commainferior Agravesmall
    Aacutesmall Acircumflexsmall Atildesmall Adieresissmall

    Aringsmall AEsmall Ccedillasmall Egravesmall
    Eacutesmall Ecircumflexsmall Edieresissmall Igravesmall
    Iacutesmall Icircumflexsmall Idieresissmall Ethsmall
    Ntildesmall Ogravesmall Oacutesmall Ocircumflexsmall

    Otildesmall Odieresissmall OEsmall Oslashsmall
    Ugravesmall Uacutesmall Ucircumflexsmall Udieresissmall
    Yacutesmall Thornsmall Ydieresissmall 001.000
    001.001 001.002 001.003 Black

    Bold Book Light Medium
    Regular Roman Semibold
);

#-----------------------------------------------------------------------
#
#-----------------------------------------------------------------------
sub get_glyph_names {
    my ($CFF, $glyph_name) = @_;

    # skip header; parse (and ignore) NAME index
    my ($rest) = _parse_index(substr $CFF, unpack '@2C', $CFF);

    # parse TopDict index
    ($rest, my @top_dict) = _parse_index($rest);
    if (@top_dict > 1) {
        warn "[WARNING] multiple fonts in single file not supported";
    }
    my %top_dict = _parse_dict($top_dict[0]);
    if ($NUM_GLYPHS != unpack 'n', substr($CFF, $top_dict{17}, 2)) {
        die "[ERROR] NumGlyphs different in 'maxp' and 'CFF' tables";
    }

    # parse String index
    ($rest, my @strings) = _parse_index($rest);
    @strings = (@STANDARD_STRINGS, @strings);

    my $charset = substr $CFF, $top_dict{15};
    my $format = unpack 'C', $charset;
    if ($format == 0) {
        my @codes = unpack "\@1n@{[ $NUM_GLYPHS - 1 ]}", $charset;
        @$glyph_name = @strings[0, @codes];
    }
    elsif ($format == 1) {
        my $i = 0;
        $glyph_name->[$i++] = $strings[0];
        for (my $j = 0; $i < $NUM_GLYPHS; $j++) {
            my ($first, $n_left)
                = unpack "\@@{[ 1 + 3*$j ]}nC", $charset;
            $glyph_name->[$i + $_] = $strings[$first + $_]
                for 0 .. $n_left;
            $i += 1 + $n_left;
        }
    }
    elsif ($format == 2) {
        my $i = 0;
        $glyph_name->[$i++] = $strings[0];
        for (my $j = 0; $i < $NUM_GLYPHS; $j++) {
            my ($first, $n_left)
                = unpack "\@@{[ 1 + 4*$j ]}nn", $charset;
            $glyph_name->[$i + $_] = $strings[$first + $_]
                for 0 .. $n_left;
            $i += 1 + $n_left;
        }
    }
    else {
        warn "[ERROR] invalid CharsetFormat '$format' ignored";
    }

    return;
}

#-----------------------------------------------------------------------
# Parse Adobe's INDEX format (see CFF spec); return "rest" plus data array
#-----------------------------------------------------------------------
sub _parse_index {
    my $index = shift;

    my ($count, $off_size) = unpack 'nC', $index;
    my @offsets = unpack "\@3(a$off_size)@{[ $count + 1 ]}", $index;
    if    ($off_size == 1) { $_ = unpack 'C', $_ for @offsets }
    elsif ($off_size == 2) { $_ = unpack 'n', $_ for @offsets }
    elsif ($off_size == 4) { $_ = unpack 'N', $_ for @offsets }
    elsif ($off_size == 3) {
        for my $offset (@offsets) {
            my @bytes = map 'C3', $offset;
            $offset = ($bytes[0] << 16) + ($bytes[1] << 8) + $bytes[2];
        }
    }
    else {
        warn "[ERROR] invalid OffSize $off_size ignored";
    }
    $_ += 2 + $off_size * ($count + 1) for @offsets;

    my @data;
    for my $i (0 .. $count - 1) {
        $data[$i]
            = substr $index, $offsets[$i], $offsets[$i + 1] - $offsets[$i];
    }

    return substr($index, $offsets[$count]), @data;
}

#-----------------------------------------------------------------------
# Parse Adobe's DICT format (see CFF spec); return data hash
#-----------------------------------------------------------------------
sub _parse_dict {
    my $dict = shift;

    my @bytes = unpack 'C*', $dict;
    my (@operands, %dict);
    while (@bytes) {
        if (( 0 <= $bytes[0] && $bytes[0] <= 11)
         || (13 <= $bytes[0] && $bytes[0] <= 22))
        {
            my $operator = shift @bytes;
            ($dict{$operator} = join q{ }, @operands) =~ s/^\s+//xms;
            @operands = ();
        }
        elsif ($bytes[0] == 12) {
            my $operator = join q{ }, splice @bytes, 0, 2;
            ($dict{$operator} = join q{ }, @operands) =~ s/^\s+//xms;
            @operands = ();
        }
        elsif ($bytes[0] == 28
           ||  $bytes[0] == 29
           ||  $bytes[0] == 30
           || (32 <= $bytes[0] && $bytes[0] <= 254))
        {
            push @operands, _get_number(\@bytes);
        }
        else {
            warn "[ERROR] invalid byte $bytes[0] in DICT ignored";
            shift @bytes;
        }
    }

    return %dict;
}

#-----------------------------------------------------------------------
# Parse Adobe's variable-length numbers (see CFF spec); shorten arg array
#-----------------------------------------------------------------------
sub _get_number {
    my $bytes = shift;

    my $b0 = shift @$bytes;
    if ($b0 == 28) {
        my ($b1, $b2) = splice @$bytes, 0, 2;
        return ($b1 << 8) | $b2;
    }
    elsif ($b0 == 29) {
        my ($b1, $b2, $b3, $b4) = splice @$bytes, 0, 4;
        return ((((($b1 << 8) + $b2) << 8) + $b3) << 8) + $b4;
    }
    elsif ($b0 == 30) {
        # Reals not implemented; just dump appropriate number of bytes
        until (($b0 & 0xf0) == 0xf0 || ($b0 & 0xf) == 0xf) {
            $b0 = shift @$bytes;
        }
    }
    elsif (32 <= $b0 && $b0 <= 246) {
        return $b0 - 139;
    }
    elsif (247 <= $b0 && $b0 <= 250) {
        my $b1 = shift @$bytes;
        return 256 * ($b0 - 247) + $b1 + 108;
    }
    elsif (251 <= $b0 && $b0 <= 254) {
        my $b1 = shift @$bytes;
        return -256 * ($b0 - 251) - $b1 - 108;
    }
}


########################################################################


package OTF::GPOS;

#-----------------------------------------------------------------------
# Return list of all Lookups from the GPOS table
#-----------------------------------------------------------------------
sub get_lookups {
    my $GPOS = shift;

    my $lookup_list = substr $GPOS, unpack '@8n', $GPOS;
    my @lookup_offsets = unpack 'n/n', $lookup_list;

    return map { substr $lookup_list, $_ } @lookup_offsets;
}

#-----------------------------------------------------------------------
# Return list of all LookupListIndices pointed to by 'kern' feature
#-----------------------------------------------------------------------
sub get_lookup_list_indices {
    my $GPOS = shift;

    my $feature_list = substr $GPOS, unpack '@6n', $GPOS;
    my %lookup_list_index;
    for my $feature_record (unpack 'n/(a6)', $feature_list) {
        my ($tag, $offset) = unpack 'a4n', $feature_record;
        next if $tag ne 'kern';

        my $feature = substr $feature_list, $offset;
        my @lookup_list_indices = unpack '@2n/n', $feature;
        $lookup_list_index{$_} = 1 for @lookup_list_indices;
    }

    return keys %lookup_list_index;
}

#-----------------------------------------------------------------------
# Return list of all subtables in Lookup table
#-----------------------------------------------------------------------
sub get_subtables {
    my $lookup = shift;

    my ($lookup_type, @subtable_offsets) = unpack 'n@4n/n', $lookup;
    if ($lookup_type != 2) {
        warn "[WARNING] LookupType $lookup_type not implemented";
        return;
    }

    return map { substr $lookup, $_ } @subtable_offsets;
}

#-----------------------------------------------------------------------
# Parse subtable in PairPosFormat 1, store kern pairs in global %kern
#-----------------------------------------------------------------------
sub parse_pos_format_1 {
    my $subtable = shift;

    my ($coverage_offset, $value_format_1, $value_format_2, @pair_set_offsets)
        = unpack '@2nnnn/n', $subtable;

    my @coverage = _get_coverage(substr $subtable, $coverage_offset);
    my @pair_sets = map { substr $subtable, $_ } @pair_set_offsets;
    if (@coverage != @pair_sets) {
        warn "[ERROR] Coverage table doesn't match PairSet table";
        return;
    }

    my ($record_size, $value_offset)
        = _parse_value_formats($value_format_1, $value_format_2, 2, 2);

    while (1) {
        my $pair_set = shift @pair_sets or last;
        my $first = shift @coverage;

        my @pair_value_records = unpack "n/(a$record_size)", $pair_set;

        for my $pair_value_record (@pair_value_records) {
            my ($second, $value)
                = unpack "n\@${value_offset}s>", $pair_value_record;
            next if $value == 0;
            $kern{$first}{$second} ||= 1000 * $value / $UNITS_PER_EM;
        }
    }

    return;
}

#-----------------------------------------------------------------------
# Parse subtable in PairPosFormat 2, store kern pairs in global %kern
#-----------------------------------------------------------------------
sub parse_pos_format_2 {
    my $subtable = shift;

    my ($coverage_offset, $value_format_1, $value_format_2,
        $class_def_1, $class_def_2, $class_1_count, $class_2_count)
        = unpack '@2nnnnnnn', $subtable;

    my @coverage = _get_coverage(substr $subtable, $coverage_offset);

    my ($class_2_record_size, $value_offset)
        = _parse_value_formats($value_format_1, $value_format_2, 0, 0);

    my @class_1 = _get_class(substr $subtable, $class_def_1);
    my @class_2 = _get_class(substr $subtable, $class_def_2);

    my $class_1_record_size = $class_2_count * $class_2_record_size;
    my @class_1_records
        = unpack "\@16(a$class_1_record_size)$class_1_count", $subtable;

    for my $class_1 (0 .. $class_1_count - 1) {
        my $class_1_record = $class_1_records[$class_1];
        my @class_2_records
            = unpack "(a$class_2_record_size)$class_2_count", $class_1_record;

        for my $class_2 (0 .. $class_2_count - 1) {
            my $class_2_record = $class_2_records[$class_2];
            my $value = unpack "\@${value_offset}s>", $class_2_record;
            next if $value == 0;
            $value = 1000 * $value / $UNITS_PER_EM;

            my @first  = grep { $class_1[$_] == $class_1 } @coverage;
            my @second = grep { $class_2[$_] == $class_2 } 0 .. $#class_2;

            for my $first (@first) {
                for my $second (@second) {
                    $kern{$first}{$second} ||= $value;
                }
            }
        }
    }

    return;
}

#-----------------------------------------------------------------------
# Get class number for all glyphs
#-----------------------------------------------------------------------
sub _get_class {
    my $class = shift;

    my @class = (0) x $NUM_GLYPHS;

    my $class_format = unpack 'n', $class;
    if ($class_format == 1) {
        my ($start_glyph, @class_value) = unpack '@2nn/n', $class;
        @class[$start_glyph .. $start_glyph + $#class_value]
            = @class_value;
    }
    elsif ($class_format == 2) {
        my @class_ranges = unpack '@2n/(a6)', $class;
        for my $class_range (@class_ranges) {
            my ($start, $end, $class) = unpack 'nnn', $class_range;
            @class[$start .. $end] = ($class) x ($end - $start + 1);
        }
    }
    else {
        warn "[ERROR] invalid ClassFormat '$class_format' ignored";
        return;
    }

    return @class;
}


#-----------------------------------------------------------------------
# Determine size of ValueRecord and offset of XAdvance value in it
#-----------------------------------------------------------------------
sub _parse_value_formats {
    my ($value_format_1, $value_format_2, $record_size, $value_offset) = @_;

    unless ($value_format_1 & 0x4 && $value_format_2 == 0) {
        warn "[WARNING] ValueFormat ($value_format_1, ",
             "$value_format_2) not implemented";
        return;
    }

    for my $bit ((0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80)) {
        $record_size += 2 if $value_format_1 & $bit;
    }
    for my $bit ((0x1, 0x2)) {
        $value_offset += 2 if $value_format_1 & $bit;
    }

    return ($record_size, $value_offset);
}

#-----------------------------------------------------------------------
# Return a list of GlyphIDs in a Coverage table
#-----------------------------------------------------------------------
sub _get_coverage {
    my $coverage = shift;

    my $coverage_format = unpack 'n', $coverage;
    if ($coverage_format == 1) {
        return unpack '@2n/n', $coverage;
    }
    elsif ($coverage_format == 2) {
        my @range_records = unpack '@2n/(a6)', $coverage;

        return map { my ($start, $end) = unpack 'nn', $_;
                     $start .. $end;
                   }
                   @range_records;
    }
    else {
        warn "[WARNING] unknown CoverageFormat $coverage_format ignored";
    }
}


########################################################################


package OTF::Kern;

#-----------------------------------------------------------------------
# Parse "kern"table, store kern pairs in global %kern
#-----------------------------------------------------------------------
sub parse_kerntable {
    my $kern = shift;

    my $num_tables = unpack '@2n', $kern;
    my $start_subtable = 4;
    for my $i (0 .. $num_tables - 1) {
        my $subtable = substr $kern, $start_subtable;
        my ($length, $coverage) = unpack '@2nn', $subtable;
        $start_subtable += $length;

        if ($coverage != 0x1) {
            warn "[WARNING] kern table format '$coverage' not implemented";
            next;
        }

        my @kern_pairs = unpack '@6nx6/(a6)', $subtable;
        for my $kern_pair (@kern_pairs) {
            my ($first, $second, $value) = unpack 'nns>', $kern_pair;
            next if $value == 0;

            $kern{$first}{$second} ||= 1000 * $value / $UNITS_PER_EM;
        }
    }

    return;
}


########################################################################


package main;

main();

__END__


########################################################################


    To create the documentation:

    pod2man --center="Marc Penninga" --release="fontools" --section=1 \
        ot2kpx - | groff -Tps -man - | ps2pdf - ot2kpx.pdf

=pod

=head1 NAME

ot2kpx - extract kerning information from OpenType fonts


=head1 SYNOPSIS

B<ot2kpx> [ I<-afm> | I<-kpx> | I<-lua> ] B<< <fontfile> >>


=head1 DESCRIPTION

B<ot2kpx> extract the kerning data from OpenType fonts and prints it
to C<stdout>, either in Adobe's KPX format (for adding to an F<afm> file)
or as a Luatex custom feature, for use with the C<\directlua> command.


=head1 OPTIONS AND ARGUMENTS

=over 4

=item B<-help>

Print a short help text and exit.

=item B<-version>

Print B<ot2kpx>'s version and exit.

=item B<-afm>, B<-kpx>

Output the kerning data in Adobe's KPX format, as used in F<afm> files.
This is the default output format.

=item B<-lua>

Output the kerning data as a Luatex custom font feature,
to be included in a C<\directlua> command.

=item B<< <fontfile> >>

The OpenType font (both F<otf> and F<ttf> format are supported).

=back


=head1 RESTRICTIONS

=over 4

=item B<->

B<ot2kpx> doesn't implement all of the OpenType specification.
Things that are missing include: support for font files containing
multiple fonts, LookupTables with LookupTypes other than 2,
"kern" tables with format other than 0 and ValueRecords with
other types of data than just XAdvance data.

Most of these limitations won't matter, since the missing features
are rare (the only fonts I know of that use them are the non-western fonts
that come with Adobe Reader). Furthermore, many of these features define
(according to the OpenType specification) I<"subtle, device-dependent
adjustments at specific font sizes or device resolutions">;
since there's no way to express such adjustments in F<afm> format,
ignoring them seems to be the only option anyway.

=item B<->

B<ot2kpx> collects kerning data first from the "kern" table, then from
all LookupTables associated with the "kern" feature; if a kerning pair
occurs multiple times, the first value seen is chosen.
There are (or may be) several issues with this approach:

=over 4

=item -

The OpenType specification says that fonts in F<otf> format shouldn't
use the "kern" table at all, just the lookups from the "GPOS" table.
Many such fonts do, however, contain a "kern" table, but no "GPOS" table;
so we use the "kern" table anyway.

=item -

Instead of reading all LookupTables, it might be better to let the user
specify a script and language and process only the LookupTables for
those values.
However, at least in the fonts I checked, all script/language combinations
eventually point to the I<same> "kern" LookupTables, so this approach
wouldn't make any difference (apart from further complicating the code).

=back

=back


=head1 AUTHOR

Marc Penninga <marcpenninga@gmail.com>


=head1 COPYRIGHT

Copyright (C) 2005-2021 Marc Penninga.


=head1 LICENSE

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation, either version 2 of the License,
or (at your option) any later version.
A copy of the GNU General Public License is included with B<ot2kpx>;
see the file F<GPLv2.txt>.


=head1 DISCLAIMER

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU General Public License for more details.


=head1 VERSION

This document describes B<ot2kpx> version 20211115.


=head1 RECENT CHANGES

(See the source code for the rest of the story.)

=over 12

=item I<2019-05-20>

Added the I<-version> option.

=item I<2019-04-15>

Added the I<-lua> command-line option to get output in Luatex's
custom feature format.

=back


=begin Really_old_history

=over 12

=item I<2013-08-07>

Replaced all C<given/when> constructions in the source code by C<if>'s,
to avoid warnings about experimental features in Perl 5.18 and later.

=item I<2012-02-01>

Refactored the code, and fixed a number of bugs in the process.
Updated the documentation.

=item I<2005-01-10>

First version

=item I<2005-02-18>

Rewrote some of the code

=item I<2005-03-08>

Input files searched via B<kpsewhich> (where available)

=item I<2005-03-15>

Input files searched using B<kpsewhich> or B<findtexmf>

=item I<2005-03-21>

Test if GPOS table is present before trying to read it

=item I<2005-04-29>

Improved the documentation

=item I<2005-05-25>

Changed warning that's given when the font contains no GPOS table, to an
informational message.

=item I<2005-07-29>

A few updates to the documentation

=back

=cut