Font::TTF::GSUB(3pm) User Contributed Perl Documentation Font::TTF::GSUB(3pm)
NAME
Font::TTF::GSUB - Module support for the GSUB table in conjunction with
TTOpen
DESCRIPTION
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!
INSTANCE VARIABLES
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
lookups.
ACTION_TYPE
This is a string taking one of 4 values indicating the nature of
the information in the ACTION array of the rule:
g The action contains a string of glyphs to replace the match
string by
l The action array contains a list of offsets and lookups to
run, in order, on the matched string
a The action array is an unordered set of optional
replacements for the matched glyph. The application should
make the selection somehow.
o 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
r 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
substitution.
MATCH_TYPE
This indicates which type of information the various MATCH arrays
(MATCH, PRE, POST) hold in the rule:
g The array holds a string of glyph ids which should match
exactly
c The array holds a sequence of class definitions which each
glyph should correspondingly match to
o The array holds offsets to coverage tables
CORRESPONDANCE TO LAYOUT TYPES
The following table gives the values for ACTION_TYPE and MATCH_TYPE for
each of the 12 different lookup types found in the GSUB table
definition:
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 table.
METHODS
$t->read_sub($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.
$t->extension
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.
AUTHOR
Martin Hosken <http://scripts.sil.org/FontUtils>.
LICENSING
Copyright (c) 1998-2016, 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.
perl v5.32.0 2020-12-27 Font::TTF::GSUB(3pm)
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