Microsoft Typography
February 2002

This document presents information that will help font developers create or support OpenType fonts for all Thai script languages covered by the Unicode Standard. Thai script is used to write Thai, as well as other Southeast Asian languages such as Pali and Sanskrit.

This is a multi-page specification. To access specific pages, use the Contents section below, or the navigation bar at the bottom of each page.

Contents

• Introduction
• Shaping Engine
• Features
• Appendix

Introduction

Font developers will learn how to encode complex script features in their fonts, choose character sets, organize font information, and use existing tools to produce Thai fonts. Registered features of the Thai script are defined and illustrated, encodings are listed, and templates are included for compiling Thai layout tables for OpenType fonts.

This document also presents information about the Thai OpenType shaping engine of Uniscribe, the Windows component responsible for text layout.

In addition to being a primer and specification for the creation and support of Thai fonts, this document is intended to more broadly illustrate the OpenType Layout architecture, feature schemes, and operating system support for shaping and positioning text.

Glossary

The following terms are useful for understanding the layout features and script rules discussed in this document.

Base Glyph - Any glyph that can have a diacritic mark above or below it. Layout operations are defined in terms of a base glyph, not a base character, as a ligature may act as the base.

Character - Each character represents a Unicode character code point. For example, the 'ko kai' character is U+0E01.

Combining Mark - A vowel sign or tone mark, positioned above or below a character to provide pronunciation guidance.

Cluster - The effective "unit" of Thai writing systems, consisting of a consonant, vowel signs, combining tone marks, and independent vowel letters.

Glyph - A glyph represents a form of one or more characters.