NAME

Font::TTF::Scripts::Volt - Memory representation of a Volt based font

SYNOPSIS

use Font::TTF::Scripts::Volt;
$fv = Font::TTF::Scripts::Volt->read_font($ttf_file, $ap_file, %opts);
$dat = $fv->parse_volt;
@map = $fv->align_glyphs($dat);
$fv->merge_volt($dat, \@map);
$fv->make_anchors;
$fv->make_groups;
$fv->make_lookups;
$res = $fv->out_volt;

DESCRIPTION

Font::TTF::Scripts::Volt is based on and inherits from Font::TTF::Scripts::AP and as such contains all the information in such an object. The read method does little beyond calling the corresponding AP method.

The real power in this module is in the Volt parser that can parse Volt source code. It does it rather slowly, but it does do it and reads it into an internal format. This format can be output and can be merged into an existing font using merge_volt. From there it can be output as Volt source. The data structures added represent the Volt source.

glyphs

This is shared with the glyphs array from AP but adds a few Volt specific sub values

uni

May be an array of values as well as a single value

type

MARK, BASE, etc.

component_num

Number of components in a ligature

name

Volt name in the source

scripts

This is a hash of script structures keyed off the script name as used in Volt it contains

tag

Four letter script tag

langs

An array of language structures consisting of (nearly there)

name

Language name as in Volt

tag

Language tag that ends up in the font

<feature name>

Hash of features by name each containing (last one)

name

Name of the feature as used to reference it

tag

Feature tag that ends up in the font

lookups

Array of names of lookups associated with this feature

anchors

This is a hash by anchor name that contains a sub hash with the following elements:

pos

A pos type containing the actual position of the anchor point

locked

Contains LOCKED if the anchor point is locked

component

Contains the component number for a ligature or 1 normally.

groups

A hash of group definitions by name. The contents is an array of <context> corresponding to each element in the group's defining enum.

lookups

An array of lookups in the order they appear in the Volt source. Each lookup consists of

id

Lookup name

base

Contains PROCESS_BASE if that is in the lookup

marks

Contains either PROCESS_MARKS or SKIP_MARKS

all

Contains a group name or ALL according to what is to be processed

dir

Contains LTR or RTL

contexts

Contains an array of contexts as per IN_CONTEXT. Each element of the array is itself an array corresponding to the elements in a context. In turn each of these elements consists of an array with two elements: A string LEFT or RIGHT and a context

lookup

This is an array of subactions within the lookup. Each element of this array is itself an array with a first element giving the lookup type: sub or pos and the second element being the content of the lookup.

For a sub lookup the second element is an array each item of which is a substitution pair held in an array. The first element of this substitution pair is an array of contexts to be substituted and the second element is an array of contexts that the subsitutition is substituted with.

For a pos lookup, the second element is an array hashes, one per sublookup. The elements in the hash are dependent on the type of positioning but have consistent meaning:

type

The type of positioning. May be ATTACH, ATTACH_CURSIVE, ADJUST_SINGLE, ADJUST_PAIR.

context

Gives the context glyph for ATTACH and ADJUST_SINGLE lookups and consists of a single context

context1

The first context glyph for an ADJUST_PAIR. It consists of an array of contexts which are referenced by number according to their index (starting at 1) in the positioning.

context2

The second context glyph for an ADJUST_PAIR. It consists of an array of contextss which correspond to the second number in a position.

exits

An array of contexts one for each glyph with an exit anchor. Used only in ATTACH_CURSIVE

enters

An array of contexts one for each glyph with an entry anchor. Used only in ATTACH_CURSIVE

to

Used in an ATTACH to specify which glyphs the context glyphs are attached to and with which anchor point. Each element of this array is an array with two elements: a context to specify the glyph moving (the base glyph is specified by the context hash entry) and the name of the anchor point used to link the two. The base glyph has an anchor with the anchor name and the second glyph has an anchor with the anchor named prefixed by MARK_

adj

An adjustment is used in a ADJUST_SINGLE as an array of positioning elements of type pos each one corresponding to a context in the context array.

For an ADJUST_PAIR the adj is an array of arrays. Each sub array has 3 elements: first index into the context1 array (starting at 1), second index into the context2 array (starting at 1) and a pos to specify the actual adjustment of those two glyphs.

info

The info hash contains some global information for the whole font with the following hash elements:

ppos

Specifies the pixesl per em for positioning purpsoes

grid

Specifies the pixels per em for the grid

pres

Specifies the presentation pixels per em

cmap

This is an array of cmap entries, each of which is an array of 3 numbers.

In addition to extra entries in the main object there are two types that are used in various places:

Context

A context consists of an array with two elements. The first element gives the type of the context item and the second the value. The context types are:

GLYPH

The second array element contains a glyph id. Note it does not contain a glyph name. The name is resolved to an id in the parser and converted back to a name during output.

GROUP

The second array element is a string holding the name of the group being referenced

RANGE

The second two array elements are the first and last glyph id for the range. Ranges are particularly difficult to work with when merging different glyph arrays so should be avoided

ENUM

An enum is a way of embedding a list of contexts within a context. The remaining elements in the array are contexts

Pos

A positioning element is a glorious animal. You would think that it could just be an x and y co-ordinate. You would be so wrong! A pos is a hash with three elements: x, y and adv. adv specifies changes to the advance width of a glyph in ADJUST_PAIR.

Each of these hash entries is an array. The first element of the array is the actual co-ordinate value. The second is an optionally empty array of adjustments to that co-ordinate. Each element of that array is a two element array of the adjust value and the ppem value at which the adjustment occurs.

$f->parse_volt([$vtext])

Parses volt source. If no $vtext then take it from the TSIV table in the font.