Components of Multilingual Software development using Unicode

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Components of Multilingual Software development
using Unicode

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Introduction

• Unicode is the only format that supports almost
  all characters that we use today. All major
  operating systems and programming languages
  support or will support Unicode in near future. I
  will discuss Microsoft based technologies for
  making multilingual applications.

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Main Components

• Unicode
• Uniscribe
• OpenType fonts

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Basic flow
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Unicode

• The Unicode Standard is a character set for data
  interchange in plain text format. It contains no
  attributes regarding language, display format or
  rendering.
• In order to avoid duplication of characters,
  Unicode encodes text by script, not by language.

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Uniscribe

• A rendering process is needed for displaying
  Unicode-based characters of complex scripts. This
  process maps characters to glyphs.
• Options for processing complex scripts
• Text functions
• Edit controls
• Rich edit controls

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OpenType Fonts

• Glyphs
• Encoded, Non-encoded
• Simple, Ligature, Mark
• OpenType Library Services for Arabic script
  (OTLS)
• Shaping features
• Positioning features

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OpenType Fonts (cont.)

• Layout features within OpenType fonts are
  organized by scripts and languages, allowing a
  single font to support multiple writing systems,
  even within the same script.
• All features are applied on Glyphs and not on
  Characters.
• When a character is typed, its keystroke value
  is preserved and glyphs are displayed according
  to the layouts.

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Encoded Glyphs

• Any character in Unicode.
• One glyph may have more than one code points.
• For Arabic script based fonts, only characters in
  Arabic code page (0600-06FF) should be encoded
  because Arabic presentation forms contain
  different shapes of characters and ligatures.
  These issues are handled by Positioning and
  Shaping features.

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Non-Encoded Glyphs

• Contextual shapes of all desired characters.
• Ligatures

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Other Glyphs

• Simple Glyphs
• Glyphs for single character alphabets and
  numbers.
• Ligature Glyphs
• Multi-character glyphs, normally combination of
  characters.
• Mark Glyphs
• Zero width glyphs like Airab

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About OTLS

• A font contains support for some scripts, each
  script contains support for some languages and
  OTLS are defined for each language.
• Every script contains a default language entry.
  OTLS defined for this language are used for all
  languages of that script.
• This helps making single font supporting
  languages having same glyphs with different
  behavior.

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Shaping features

• ccmp (Character composition and decomposition)
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• isol (Isolated character form substitution)
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• fina (Final character form substitution )
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Shaping features (cont.)

• medi (Medial character form substitution)
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• Init (Initial character form substitution )
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• rlig (Required ligature substitution )
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Positioning features

• curs (Cursive positioning)
• kern (Kerning)
• mark (Mark to base positioning)
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• mkmk (Mark to mark positioning)
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Other features of OpenType

• OpenType fonts can be embedded directly to the
  document
• Microsoft Word documents
• HTML documents

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Related technologies

• Pango
• An open-source framework for the layout and
  rendering of internationalized text for GTK and
  GNOME.
• It supports OpenType fonts.

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Related technologies (cont.)

• Pango

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