.\" Automatically generated by Pod::Man 4.11 (Pod::Simple 3.35)
.\"
.\" Standard preamble:
.\" ========================================================================
.de Sp \" Vertical space (when we can't use .PP)
.if t .sp .5v
.if n .sp
..
.de Vb \" Begin verbatim text
.ft CW
.nf
.ne \\$1
..
.de Ve \" End verbatim text
.ft R
.fi
..
.\" Set up some character translations and predefined strings. \*(-- will
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
.\" double quote, and \*(R" will give a right double quote. \*(C+ will
.\" give a nicer C++. Capital omega is used to do unbreakable dashes and
.\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff,
.\" nothing in troff, for use with C<>.
.tr \(*W-
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
.ie n \{\
. ds -- \(*W-
. ds PI pi
. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
. if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
. ds L" ""
. ds R" ""
. ds C` ""
. ds C' ""
'br\}
.el\{\
. ds -- \|\(em\|
. ds PI \(*p
. ds L" ``
. ds R" ''
. ds C`
. ds C'
'br\}
.\"
.\" Escape single quotes in literal strings from groff's Unicode transform.
.ie \n(.g .ds Aq \(aq
.el .ds Aq '
.\"
.\" If the F register is >0, we'll generate index entries on stderr for
.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index
.\" entries marked with X<> in POD. Of course, you'll have to process the
.\" output yourself in some meaningful fashion.
.\"
.\" Avoid warning from groff about undefined register 'F'.
.de IX
..
.nr rF 0
.if \n(.g .if rF .nr rF 1
.if (\n(rF:(\n(.g==0)) \{\
. if \nF \{\
. de IX
. tm Index:\\$1\t\\n%\t"\\$2"
..
. if !\nF==2 \{\
. nr % 0
. nr F 2
. \}
. \}
.\}
.rr rF
.\" ========================================================================
.\"
.IX Title "Font::TTF::GPOS 3"
.TH Font::TTF::GPOS 3 "2016-08-03" "perl v5.26.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Font::TTF::GPOS \- Support for Opentype GPOS tables in conjunction with TTOpen
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1GPOS\s0 table is one of the most complicated tables in the \s-1TTF\s0 spec and the
corresponding data structure abstraction is also not trivial. While much of the
structure of a \s-1GPOS\s0 is shared with a \s-1GSUB\s0 table via the Font::TTF::Ttopen
.SH "INSTANCE VARIABLES"
.IX Header "INSTANCE VARIABLES"
Here we describe the additions and lookup specific information for \s-1GPOS\s0 tables.
Unfortunately there is no one abstraction which seems to work comfortable for
all \s-1GPOS\s0 tables, so we will also examine how the variables are used for different
lookup types.
.PP
The following are the values allowed in the \s-1ACTION_TYPE\s0 and \s-1MATCH_TYPE\s0 variables:
.IP "\s-1ACTION_TYPE\s0" 4
.IX Item "ACTION_TYPE"
This can take any of the following values
.RS 4
.IP "a" 8
.IX Item "a"
The \s-1ACTION\s0 is an array of anchor tables
.IP "o" 8
.IX Item "o"
Offset. There is no \s-1RULE\s0 array. The \s-1ADJUST\s0 variable contains a value record (see
later in this description)
.IP "v" 8
.IX Item "v"
The \s-1ACTION\s0 is a value record.
.IP "p" 8
.IX Item "p"
Pair adjustment. The \s-1ACTION\s0 contains an array of two value records for the matched
two glyphs.
.IP "e" 8
.IX Item "e"
Exit and Entry records. The \s-1ACTION\s0 contains an array of two anchors corresponding
to the exit and entry anchors for the glyph.
.IP "l" 8
.IX Item "l"
Indicates a lookup based contextual rule as per the \s-1GSUB\s0 table.
.RE
.RS 4
.RE
.IP "\s-1MATCH_TYPE\s0" 4
.IX Item "MATCH_TYPE"
This can take any of the following values
.RS 4
.IP "g" 8
.IX Item "g"
A glyph array
.IP "c" 8
.IX Item "c"
An array of class values
.IP "o" 8
.IX Item "o"
An array of coverage tables
.RE
.RS 4
.RE
.PP
The following variables are added for Attachment Positioning Subtables:
.IP "\s-1MATCH\s0" 4
.IX Item "MATCH"
This contains an array of glyphs to match against for all \s-1RULES.\s0 It is much like
having the same \s-1MATCH\s0 string in all \s-1RULES.\s0 In the cases it is used so far, it only
ever contains one element.
.IP "\s-1MARKS\s0" 4
.IX Item "MARKS"
This contains a Mark array consisting of each element being a subarray of two
elements:
.RS 4
.IP "\s-1CLASS\s0" 8
.IX Item "CLASS"
The class that this mark uses on its base
.IP "\s-1ANCHOR\s0" 8
.IX Item "ANCHOR"
The anchor with which to attach this mark glyph
.RE
.RS 4
.Sp
The base table for mark to base, ligature or mark attachment positioning is
structured with the \s-1ACTION\s0 containing an array of anchors corresponding to each
attachment class. For ligatures, there is more than one \s-1RULE\s0 in the \s-1RULE\s0 array
corresponding to each glyph in the coverage table.
.RE
.PP
Other variables which are provided for informational purposes are:
.IP "\s-1VFMT\s0" 4
.IX Item "VFMT"
Value format for the adjustment of the glyph matched by the coverage table.
.IP "\s-1VFMT2\s0" 4
.IX Item "VFMT2"
Value format used in pair adjustment for the second glyph in the pair
.SS "Value Records"
.IX Subsection "Value Records"
There is a subtype used in \s-1GPOS\s0 tables called a value record. It is used to adjust
the position of a glyph from its default position. The value record is variable
length with a bitfield at the beginning to indicate which of the following
entries are included. The bitfield is not stored since it is recalculated at
write time.
.IP "XPlacement" 4
.IX Item "XPlacement"
Horizontal adjustment for placement (not affecting other unattached glyphs)
.IP "YPlacement" 4
.IX Item "YPlacement"
Vertical adjustment for placement (not affecting other unattached glyphs)
.IP "XAdvance" 4
.IX Item "XAdvance"
Adjust the advance width glyph (used only in horizontal writing systems)
.IP "YAdvance" 4
.IX Item "YAdvance"
Adjust the vertical advance (used only in vertical writing systems)
.IP "XPlaDevice" 4
.IX Item "XPlaDevice"
Device table for device specific adjustment of horizontal placement
.IP "YPlaDevice" 4
.IX Item "YPlaDevice"
Device table for device specific adjustment of vertical placement
.IP "XAdvDevice" 4
.IX Item "XAdvDevice"
Device table for device specific adjustment of horizontal advance
.IP "YAdDevice" 4
.IX Item "YAdDevice"
Device table for device specific adjustment of vertical advance
.IP "XIdPlacement" 4
.IX Item "XIdPlacement"
Horizontal placement metric id (for Multiple Master fonts \- but that is all I know!)
.IP "YIdPlacement" 4
.IX Item "YIdPlacement"
Vertical placement metric id
.IP "XIdAdvance" 4
.IX Item "XIdAdvance"
Horizontal advance metric id
.IP "YIdAdvance" 4
.IX Item "YIdAdvance"
Vertical advance metric id
.SH "CORRESPONDANCE TO LAYOUT TYPES"
.IX Header "CORRESPONDANCE TO LAYOUT TYPES"
Here is what is stored in the \s-1ACTION_TYPE\s0 and \s-1MATCH_TYPE\s0 for each of the known
\&\s-1GPOS\s0 subtable types:
.PP
.Vb 3
\& 1.1 1.2 2.1 2.2 3 4 5 6 7.1 7.2 7.3 8.1 8.2 8.3
\& ACTION_TYPE o v p p e a a a l l l l l l
\& MATCH_TYPE g c g c o g c o
.Ve
.SH "METHODS"
.IX Header "METHODS"
.SS "read_sub"
.IX Subsection "read_sub"
Reads the subtable into the data structures
.ie n .SS "$t\->extension"
.el .SS "\f(CW$t\fP\->extension"
.IX Subsection "$t->extension"
Returns the table type number for the extension table
.ie n .SS "$t\->out_sub"
.el .SS "\f(CW$t\fP\->out_sub"
.IX Subsection "$t->out_sub"
Outputs the subtable to the given filehandle
.ie n .SS "$t\->read_value($format, $base, $lookup, $fh)"
.el .SS "\f(CW$t\fP\->read_value($format, \f(CW$base\fP, \f(CW$lookup\fP, \f(CW$fh\fP)"
.IX Subsection "$t->read_value($format, $base, $lookup, $fh)"
Reads a value record from the current location in the file, according to the
format given.
.ie n .SS "$t\->read_delta($offset, $base, $lookup, $fh)"
.el .SS "\f(CW$t\fP\->read_delta($offset, \f(CW$base\fP, \f(CW$lookup\fP, \f(CW$fh\fP)"
.IX Subsection "$t->read_delta($offset, $base, $lookup, $fh)"
Reads a delta (device table) at the given offset if it hasn not already been read.
Store the offset and item in the lookup cache ($lookup\->{' \s-1CACHE\s0'})
.ie n .SS "$t\->read_anchor($offset, $base, $lookup, $fh)"
.el .SS "\f(CW$t\fP\->read_anchor($offset, \f(CW$base\fP, \f(CW$lookup\fP, \f(CW$fh\fP)"
.IX Subsection "$t->read_anchor($offset, $base, $lookup, $fh)"
Reads an Anchor table at the given offset if it has not already been read.
.ie n .SS "$t\->fmt_value"
.el .SS "\f(CW$t\fP\->fmt_value"
.IX Subsection "$t->fmt_value"
Returns the value format for a given value record
.ie n .SS "$t\->out_value"
.el .SS "\f(CW$t\fP\->out_value"
.IX Subsection "$t->out_value"
Returns the output string for the outputting of the value for a given format. Also
updates the offset cache for any device tables referenced.
.SH "AUTHOR"
.IX Header "AUTHOR"
Martin Hosken <http://scripts.sil.org/FontUtils>.
.SH "LICENSING"
.IX Header "LICENSING"
Copyright (c) 1998\-2016, \s-1SIL\s0 International (http://www.sil.org)
.PP
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 \s-1LICENSE.\s0