Font::TTF::GSUB - phpMan

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.