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Manual Reference Pages  -  FONT::TTF::KERN (3)

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Font::TTF::Kern - Kerning tables



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.


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



Reads the whole kerning table into structures


Outputs the kerning tables to the given file

CW$t->XML_element($context, CW$depth, CW$key, CW$value)

Handles outputting the kern hash into XML a little more tidily


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.


o Only supports kerning table types 0 & 2.
o No real support functions to do anything with the kerning tables yet.


Martin Hosken <>.


Copyright (c) 1998-2014, SIL International (

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.

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perl v5.20.3 FONT::TTF::KERN (3) 2014-12-10

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