font::ttf::gsub(3)
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 lookups
- and offsets 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 - 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 defini
- tions 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 11 different lookup types found
in the GSUB table definition I have: - 1.1 1.2 2 3 4 5.1 5.2 5.3 6.1 6.2
- 6.3
- ACTION_TYPE o g g a g l l l l l l
MATCH_TYPE g g c o g c 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.
$t->out_sub($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 Martin_Hosken@sil.org. See Font::TTF::Font
for copyright and licensing.