Section: User Contributed Perl Documentation (3)
Font::TTF::GSUB - Module support for the GSUB table in conjunction with TTOpen
Handles the GSUB
subtables in relation to Ttopen tables. Due to the variety of
different lookup types, the data structures are not all that straightforward,
although I have tried to make life easy for myself when using this!
The structure of a GSUB
table is the same as that given in Font::TTF::Ttopen.
Here we give some of the semantics specific to GSUB
This is a string taking one of 4 values indicating the nature of the information
in the ACTION array of the rule:
The action contains a string of glyphs to replace the match string by
The action array contains a list of offsets and lookups to run, in order, on
the matched string
The action array is an unordered set of optional replacements for the matched
glyph. The application should make the selection somehow.
The action array is empty (in fact there is no rule array for this type of
rule) and the ADJUST value should be added to the glyph id to find the replacement
glyph id value
The action array is a list of replacement glyphs in coverage order. This ACTION_TYPE
is used only for Type 8 Reverse Chaining lookups which, by design, are single glyph
This indicates which type of information the various MATCH arrays (MATCH, PRE,
POST) hold in the rule:
The array holds a string of glyph ids which should match exactly
The array holds a sequence of class definitions which each glyph should
correspondingly match to
The array holds offsets to coverage tables
CORRESPONDANCE TO LAYOUT TYPES
The following table gives the values for ACTION_TYPE
of the 12 different lookup types found in the GSUB
1.1 1.2 2 3 4 5.1 5.2 5.3 6.1 6.2 6.3 8
ACTION_TYPE o g g a g l l l l l l r
MATCH_TYPE g g c o g c o o
Hopefully, the rest of the uses of the variables should make sense from this
$t->read_sub($fh, $lookup, $index)
Asked by the superclass to read in from the given file the indexth subtable from
lookup number lookup. The file is positioned ready for the read.
Returns the table type number for the extension table
$t->out_sub($fh, $lookup, $index)
Passed the filehandle to output to, suitably positioned, the lookup and subtable
index, this function outputs the subtable to $fh
at that point.
Martin Hosken <http://scripts.sil.org/FontUtils
Copyright (c) 1998-2016, SIL
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.