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This package contains classes that implement inline text formatting.
Introduction
The job of a full-fledged layout engine can be roughly
described as the interpretation of some input, typically
mixing characters and images on which styling constraints are
applied, to produce an output which is a set of positioned
glyphs and images. To accomplish this job, a layout engine
will maintain data structures, and invoke a number of
subcomponents to modify and refine those datastructures
(e.g. a table formatter, an hyphenation engine).
A subcomponent of particular interest is an
inline text formatter: this subcomponent is
concerned with text only, and is tasked with the
selection of fonts, glyphs in those fonts, and
positions for those glyphs. ?inline? refers to
the fact that this subcomponent has a limited view of
layout: the text is set on a single infinite line,
without direct consideration of column alignment and
such. It is the job of the layout engine to slice the
output of the inline text formatter into lines, align
columns, etc.
Major components
The inline formatters implemented in this package do not have
an explicit knowledge of the data structure of the layout
engine they support. Instead, they have a view on those data
structure through the {@link
com.adobe.fontengine.inlineformatting.AttributedRun
AttributedRun} interface. This interface captures the idea of
a run of characters or glyphs, with attributes which describe
the styling constraints. The attributes are key/value pairs.
The typical client of this package will build some object that
implements the AttributedRun interface. This run contains
characters. In addition, the client sets some well-known
attributes on the run. For example, if the target formatter is
a CSS formatter, the client sets attributes such as
ElementAttributes.CSSFamily to communicate the styling
constraints to the formatter. The formatter can also be
configured with resources external to the document, such as
the set of fonts which can be used. The client then invokes
the format method of the formatter, passing it
the object implementing AttributedRun. As the
formatter does its work, it transforms the
AttributedRun, making successive decisions on how
to achieve the styling constraints. At the end, the
AttributedRun contains selected fonts, selected glyphs, and
selected positions for those glyphs.
Each formatter defines the set of styling attributes it
interprets. Those attributes are key/value pairs, where the
key is an object of type {@link
com.adobe.fontengine.inlineformatting.ElementAttribute
ElementAttribute} or {@link
com.adobe.fontengine.inlineformatting.InterElementAttribute
InterElementAttribute}. The identity of those objects defines
the styling attributes; in other words, the object {@link
com.adobe.fontengine.inlineformatting.ElementAttribute#CSS20Attribute
CSS20Attribute} (and only this object) is the key that CSS
formatters will use to retrieve the CSS properties specified
by the client. Similarly, each formatter defines the
attributes under which the result of formatting can be
accessed by the client.
AFE offers three formatters:
- {@link com.adobe.fontengine.inlineformatting.BasicFormatter}: the
client selects the font(s) with which the run must be formatted.
- {@link com.adobe.fontengine.inlineformatting.PDF16PlainTextFormatter}:
targeted at the formatting of plain text form fields in PDF 1.6.
- {@link com.adobe.fontengine.inlineformatting.PDF16RichTextFormatter}:
targeted at the formatting of rich text form fields in PDF 1.6.
Writing systems and font layout technologies
While each formatter suports a different set of styling attributes, they all
support the same set of writing systems and font layout technologies.
The following writing systems are supported:
- Latin
- Greek
- Cyrillic
- Armenian
- Georgian
- Hebrew
- Arabic
- Thai
- Lao
- Han ideographs and Kana (CCJKV)
- Korean Hangul, modern syllables only
The following font layout technologies are supported:
- OpenType layout, using 'cmap', 'GSUB', 'GPOS', 'GDEF' tables
- TrueType layout, using only the 'cmap' and 'kern' tables
- Name-keyed layout, using the names of the glyphs, interpreted according the
Adobe Glyph Naming Convention
- CID-keyed layout, using the CIDs of the glyphs, for the Adobe-Japan1,
Adobe-CNS1, Adobe-GB1, and Adobe-Korea1 ROS
The precise definitions of the writing systems, font
technologies and combinations of them which are supported are
described
here.