Figure 1a Isolated, initial, medial, and final forms of the Arabic character ha.
When performing text layout, a text-processing application evaluates the word-position contexts in which the ha character occurs, and then OpenType Layout data informs the application which glyph to substitute for each context. As shown here, the ha character will take any of four shapes, depending on whether it stands alone or whether it falls at the beginning, middle, or end of a word. For example, in Arabic, the shape of a character often varies with the character’s position in a word. Using OpenType Layout tables, fonts can support alternative forms of charcters and provide data used for accessing them. OpenType Layout addresses complex typographic requirements for correct display of many different scripts as well as for fine typography in any script. Registered OpenType Layout Tags for scripts, languages, and baselines, are documented in the chapter “OpenType Layout registered features”. See Advanced Typgraphic Tables.Ĭommon formats used in different OpenType Layout tables are documented in the “OpenType Layout Common Table Formats” chapter. The OpenType Layout tables are described in more detail in separate sections of the OpenType specification. This overview introduces the power and flexibility of the OpenType Layout font model. An open format that allows font developers to define their own typographical features.Explicit script and language information, so a text-processing application can adjust its behavior accordingly.Ability to perform two-dimensional positioning and glyph attachment.A rich mapping between characters and glyphs, allowing for ligatures, positional forms, alternates, and other substitutions.OpenType Layout tables provide advanced typographic capabilities for high-quality international typography:
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