{
    "mode": "perldoc",
    "parameter": "Font::TTF::GSUB",
    "section": "",
    "url": "https://www.chedong.com/phpMan.php/perldoc/Font%3A%3ATTF%3A%3AGSUB/json",
    "generated": "2026-06-15T14:55:09Z",
    "sections": {
        "NAME": {
            "content": "Font::TTF::GSUB - Module support for the GSUB table in conjunction with TTOpen\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "Handles the GSUB subtables in relation to Ttopen tables. Due to the variety of different lookup\ntypes, the data structures are not all that straightforward, although I have tried to make life\neasy for myself when using this!\n",
            "subsections": []
        },
        "INSTANCE VARIABLES": {
            "content": "The structure of a GSUB table is the same as that given in Font::TTF::Ttopen. Here we give some\nof the semantics specific to GSUB lookups.\n\nACTIONTYPE\nThis is a string taking one of 4 values indicating the nature of the information in the\nACTION array of the rule:\n\ng       The action contains a string of glyphs to replace the match string by\n\nl       The action array contains a list of offsets and lookups to run, in order, on the\nmatched string\n\na       The action array is an unordered set of optional replacements for the matched glyph.\nThe application should make the selection somehow.\n\no       The action array is empty (in fact there is no rule array for this type of rule) and\nthe ADJUST value should be added to the glyph id to find the replacement glyph id\nvalue\n\nr       The action array is a list of replacement glyphs in coverage order. This ACTIONTYPE\nis used only for Type 8 Reverse Chaining lookups which, by design, are single glyph\nsubstitution.\n\nMATCHTYPE\nThis indicates which type of information the various MATCH arrays (MATCH, PRE, POST) hold in\nthe rule:\n\ng       The array holds a string of glyph ids which should match exactly\n\nc       The array holds a sequence of class definitions which each glyph should\ncorrespondingly match to\n\no       The array holds offsets to coverage tables\n",
            "subsections": []
        },
        "CORRESPONDANCE TO LAYOUT TYPES": {
            "content": "The following table gives the values for ACTIONTYPE and MATCHTYPE for each of the 12 different\nlookup types found in the GSUB table definition:\n\n1.1 1.2  2  3  4  5.1 5.2 5.3  6.1 6.2 6.3  8\nACTIONTYPE    o   g   g  a  g   l   l   l    l   l   l   r\nMATCHTYPE                   g   g   c   o    g   c   o   o\n\nHopefully, the rest of the uses of the variables should make sense from this table.\n",
            "subsections": []
        },
        "METHODS": {
            "content": "$t->readsub($fh, $lookup, $index)\nAsked by the superclass to read in from the given file the indexth subtable from lookup number\nlookup. The file is positioned ready for the read.\n\n$t->extension\nReturns the table type number for the extension table\n\n$t->outsub($fh, $lookup, $index)\nPassed the filehandle to output to, suitably positioned, the lookup and subtable index, this\nfunction outputs the subtable to $fh at that point.\n",
            "subsections": []
        },
        "AUTHOR": {
            "content": "Martin Hosken <http://scripts.sil.org/FontUtils>.\n",
            "subsections": []
        },
        "LICENSING": {
            "content": "Copyright (c) 1998-2016, SIL International (http://www.sil.org)\n\nThis module is released under the terms of the Artistic License 2.0. For details, see the full\ntext of the license in the file LICENSE.\n",
            "subsections": []
        }
    },
    "summary": "Font::TTF::GSUB - Module support for the GSUB table in conjunction with TTOpen",
    "flags": [],
    "examples": [],
    "see_also": []
}