NAME

       ot2kpx - extract kerning information from OpenType fonts

SYNOPSIS

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

DESCRIPTION

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

OPTIONS AND ARGUMENTS

       -help
           Print a short help text and exit.

       -version
           Print ot2kpx's version and exit.

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

       -lua
           Output the kerning data as a Luatex custom font feature, to be included in a
           "\directlua" command.

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

RESTRICTIONS

       -   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)
           "subtle, device-dependent adjustments at specific font sizes or device resolutions";
           since there's no way to express such adjustments in afm format, ignoring them seems to
           be the only option anyway.

       -   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:

           -   The OpenType specification says that fonts in 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.

           -   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 same "kern" LookupTables, so this approach wouldn't make any difference
               (apart from further complicating the code).

AUTHOR

       Marc Penninga <marcpenninga@gmail.com>

COPYRIGHT

       Copyright (C) 2005-2023 Marc Penninga.

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 ot2kpx; see the file GPLv2.txt.

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.

VERSION

       This document describes ot2kpx version 20230201.

RECENT CHANGES

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

       2019-05-20  Added the -version option.

       2019-04-15  Added the -lua command-line option to get output in Luatex's custom feature
                   format.