NAME

       Font::TTF::Kern - Kerning tables

DESCRIPTION

       Kerning tables are held as an ordered collection of subtables each giving incremental
       information regarding the kerning of various pairs of glyphs.

       The basic structure of the kerning data structure is:

           $kern = $f->{'kern'}{'tables'}[$tnum]{'kerns'}{$leftnum}{$rightnum};

       Due to the possible complexity of some kerning tables the above information is
       insufficient. Reference also needs to be made to the type of the table and the coverage
       field.

INSTANCE VARIABLES

       The instance variables for a kerning table are relatively straightforward.

       Version
           Version number of the kerning table

       Num Number of subtables in the kerning table

       tables
           Array of subtables in the kerning table

           Each subtable has a number of instance variables.

           kern
               A two level hash array containing kerning values. The indexing is left is via left
               class and right class. It may seem using hashes is strange, but most tables are
               not type 2 and this method saves empty array values.

           type
               Stores the table type. Only type 0 and type 2 tables are specified for TrueType so
               far.

           coverage
               A bit field of coverage information regarding the kerning value. See the TrueType
               specification for details.

           Version
               Contains the version number of the table.

           Num Number of kerning pairs in this type 0 table.

           left
               An array indexed by glyph - left_first which returns a class number for the glyph
               in type 2 tables.

           right
               An array indexed by glyph - right_first which returns a class number for the glyph
               in type 2 tables.

           left_first
               the glyph number of the first element in the left array for type 2 tables.

           right_first
               the glyph number of the first element in the right array for type 2 tables.

           num_left
               Number of left classes

           num_right
               Number of right classes

METHODS

   $t->read
       Reads the whole kerning table into structures

   $t->out($fh)
       Outputs the kerning tables to the given file

   $t->XML_element($context, $depth, $key, $value)
       Handles outputting the kern hash into XML a little more tidily

   $t->minsize()
       Returns the minimum size this table can be. If it is smaller than this, then the table
       must be bad and should be deleted or whatever.

BUGS

       •   Only supports kerning table types 0 & 2.

       •   No real support functions to do anything with the kerning tables yet.

AUTHOR

       Martin Hosken Martin_Hosken@sil.org.

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.