1Font::TTF::GSUB(3)    User Contributed Perl Documentation   Font::TTF::GSUB(3)
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NAME

6       Font::TTF::GSUB - Module support for the GSUB table in conjunction with
7       TTOpen
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DESCRIPTION

10       Handles the GSUB subtables in relation to Ttopen tables. Due to the
11       variety of different lookup types, the data structures are not all that
12       straightforward, although I have tried to make life easy for myself
13       when using this!
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INSTANCE VARIABLES

16       The structure of a GSUB table is the same as that given in
17       Font::TTF::Ttopen.  Here we give some of the semantics specific to GSUB
18       lookups.
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20       ACTION_TYPE
21           This is a string taking one of 4 values indicating the nature of
22           the information in the ACTION array of the rule:
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24           g       The action contains a string of glyphs to replace the match
25                   string by
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27           l       The action array contains a list of lookups and offsets to
28                   run, in order, on the matched string
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30           a       The action array is an unordered set of optional replace‐
31                   ments for the matched glyph. The application should make
32                   the selection somehow.
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34           o       The action array is empty (in fact there is no rule array
35                   for this type of rule) and the ADJUST value should be added
36                   to the glyph id to find the replacement glyph id value
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38       MATCH_TYPE
39           This indicates which type of information the various MATCH arrays
40           (MATCH, PRE, POST) hold in the rule:
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42           g       The array holds a string of glyph ids which should match
43                   exactly
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45           c       The array holds a sequence of class definitions which each
46                   glyph should correspondingly match to
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48           o       The array holds offsets to coverage tables
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CORRESPONDANCE TO LAYOUT TYPES

51       The following table gives the values for ACTION_TYPE and MATCH_TYPE for
52       each of the 11 different lookup types found in the GSUB table defini‐
53       tion I have:
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55                       1.1 1.2 2   3   4   5.1 5.2 5.3 6.1 6.2 6.3
56         ACTION_TYPE    o   g  g   a   g    l   l   l   l   l   l
57         MATCH_TYPE                    g    g   c   o   g   c   o
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59       Hopefully, the rest of the uses of the variables should make sense from
60       this table.
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METHODS

63       $t->read_sub($fh, $lookup, $index)
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65       Asked by the superclass to read in from the given file the indexth sub‐
66       table from lookup number lookup. The file is positioned ready for the
67       read.
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69       $t->extension
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71       Returns the table type number for the extension table
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73       $t->out_sub($fh, $lookup, $index)
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75       Passed the filehandle to output to, suitably positioned, the lookup and
76       subtable index, this function outputs the subtable to $fh at that
77       point.
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AUTHOR

80       Martin Hosken Martin_Hosken@sil.org. See Font::TTF::Font for copyright
81       and licensing.
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85perl v5.8.8                       2005-06-14                Font::TTF::GSUB(3)
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