Font::TTF::GSUB(3) User Contributed Perl Documentation Font::TTF::GSUB(3)NAMEFont::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 replace‐
ments 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 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 11 different lookup types found in the GSUB table defini‐
tion 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 sub‐
table 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 Martin_Hosken@sil.org. See Font::TTF::Font for copyright
and licensing.
perl v5.8.8 2005-10-06 Font::TTF::GSUB(3)
