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Font::TTF::GSUB(3)    User Contributed Perl Documentation   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 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 v5.24.1			  2016-08-03		    Font::TTF::GSUB(3)

NAME | DESCRIPTION | INSTANCE VARIABLES | CORRESPONDANCE TO LAYOUT TYPES | METHODS | AUTHOR | LICENSING

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