For general information on OpenType Font Variations, see the chapter, OpenType Font Variations Overview. For example, a font with weight and width variations might support weights from thin to black, and widths from ultra-condensed to ultra-expanded. OpenType Font Variations allow a single font to support many design variations along one or more axes of design variation. Currently, this mechanism is used only for variable fonts using OpenType Font Variations. Lookups describe the glyphs affected by an operation, the type of operation to be applied to these glyphs, and the resulting glyph output.Ī font may also include FeatureVariations data within a GPOS or GSUB table that allows the default lookup data associated with a feature to be substituted by alternate lookup data when particular conditions apply. A ligature glyph feature substitutes the ligature for individual glyphs, and a 'mark' feature positions diacritical marks above an Arabic ligature glyph.įeatures are implemented with lookup data that the text-processing client uses to substitute and position glyphs. For instance, a default language system feature for the Arabic script substitutes initial, medial, and final glyph forms based on a glyph’s position in a word. In the absence of language-specific rules, default language system features apply to the entire script. Sample features are a 'vert' feature that substitutes vertical glyphs in Japanese, a 'liga' feature for using ligatures in place of separate glyphs, and a 'mark' feature that positions diacritical marks with respect to base glyphs in Arabic (see Figure 2c). Differences in the English and Turkish language systemsĪ language system defines features, which are typographic rules for using glyphs to represent a language. In OpenType Layout, language systems are defined within scripts. For example, Turkish has different upper and lower case relationships from most other languages written with Latin script, and that affects the glyph selection that is needed when a small caps feature ( 'smcp') is used. Glyphs in the Latin, Kanji, and Arabic scriptsĪ language system may modify the functions or appearance of glyphs in a script to represent a particular language. With OpenType Layout, multiple scripts may be supported by a single font. In contrast, three scripts-Hiragana, Katakana, and Kanji-are used to write Japanese. For instance, a single script-Latin-is used to write English, French, German, and many other languages. A script is a collection of glyphs used to represent one or more languages in written form (see Figure 2a). OpenType Layout data is organized by script, language system, typographic feature, and lookup. The OpenType Layout tables provide typographic information for properly positioning and substituting glyphs, operations that are required for accurate typography in many language environments. Separate chapters provide complete details about the GSUB, GPOS, BASE, JSTF, and GDEF tables. This chapter explains the conventions used in all OpenType Layout tables, and it describes the common table formats. These tables use some of the same data formats. OpenType Layout consists of five tables: the Glyph Substitution table (GSUB), the Glyph Positioning table (GPOS), the Baseline table (BASE), the Justification table (JSTF), and the Glyph Definition table (GDEF).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |