font::ttf::kern(3)
NAME
Font::TTF::Kern - Kerning tables
DESCRIPTION
Kerning tables are held as an ordered collection of subta
bles 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'}{$left
- num}{$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 value and then right value.
In the case of type 2 tables, the indexing 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
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. See Font::TTF::Font
for copyright and licensing.