Help-Site Computer Manuals
Software
Hardware
Programming
Networking
  Algorithms & Data Structures   Programming Languages   Revision Control
  Protocols
  Cameras   Computers   Displays   Keyboards & Mice   Motherboards   Networking   Printers & Scanners   Storage
  Windows   Linux & Unix   Mac

/var/sites/help-site.com/auto/tmp/CPAN/9677/PDF-API2-0.68/lib/PDF/API2/Basic/TTF/GPOS.pm

/var/sites/help-site.com/auto/tmp/CPAN/9677/PDF-API2-0.68/lib/PDF/API2/Basic/TTF/GPOS.pm


TITLE

PDF::API2::Basic::TTF::GPOS - Support for Opentype GPOS tables in conjunction with TTOpen


DESCRIPTION

The GPOS table is one of the most complicated tables in the TTF spec and the corresponding data structure abstraction is also not trivial. While much of the structure of a GPOS is shared with a GSUB table via the the PDF::API2::Basic::TTF::Ttopen manpage


INSTANCE VARIABLES

Here we describe the additions and lookup specific information for GPOS tables. Unfortunately there is no one abstraction which seems to work comfortable for all GPOS tables, so we will also examine how the variables are used for different lookup types.

The following are the values allowed in the ACTION_TYPE and MATCH_TYPE variables:

ACTION_TYPE
This can take any of the following values
a
The ACTION is an array of anchor tables

o
Offset. There is no RULE array. The ADJUST variable contains a value record (see later in this description)

v
The ACTION is a value record.

p
Pair adjustment. The ACTION contains an array of two value records for the matched two glyphs.

e
Exit and Entry records. The ACTION contains an array of two anchors corresponding to the exit and entry anchors for the glyph.

l
Indicates a lookup based contextual rule as per the GSUB table.

MATCH_TYPE
This can take any of the following values
g
A glyph array

c
An array of class values

o
An array of coverage tables

The following variables are added for Attachment Positioning Subtables:

MATCH
This contains an array of glyphs to match against for all RULES. It is much like having the same MATCH string in all RULES. In the cases it is used so far, it only ever contains one element.

MARKS
This contains a Mark array consisting of each element being a subarray of two elements:
CLASS
The class that this mark uses on its base

ANCHOR
The anchor with which to attach this mark glyph

The base table for mark to base, ligature or mark attachment positioning is structured with the ACTION containing an array of anchors corresponding to each attachment class. For ligatures, there is more than one RULE in the RULE array corresponding to each glyph in the coverage table.

Other variables which are provided for informational purposes are:

VFMT
Value format for the adjustment of the glyph matched by the coverage table.

VFMT2
Value format used in pair adjustment for the second glyph in the pair

Value Records

There is a subtype used in GPOS 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.

XPlacement
Horizontal adjustment for placement (not affecting other unattached glyphs)

YPlacement
Vertical adjustment for placement (not affecting other unattached glyphs)

XAdvance
Adjust the advance width glyph (used only in horizontal writing systems)

YAdvance
Adjust the vertical advance (used only in vertical writing systems)

XPlaDevice
Device table for device specific adjustment of horizontal placement

YPlaDevice
Device table for device specific adjustment of vertical placement

XAdvDevice
Device table for device specific adjustment of horizontal advance

YAdDevice
Device table for device specific adjustment of vertical advance

XIdPlacement
Horizontal placement metric id (for Multiple Master fonts - but that's all I know!)

YIdPlacement
Vertical placement metric id

XIdAdvance
Horizontal advance metric id

YIdAdvance
Vertical advance metric id


CORRESPONDANCE TO LAYOUT TYPES

Here is what is stored in the ACTION_TYPE and MATCH_TYPE for each of the known GPOS subtable types:


                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



=head1 METHODS
Programminig
Wy
Wy
yW
Wy
Programming
Wy
Wy
Wy
Wy