HarfBuzz

HarfBuzz is an open-source text shaping engine that converts Unicode text into a sequence of positioned glyphs suitable for rendering with fonts. It focuses on shaping for complex scripts and languages that require advanced typographic features, such as contextual substitutions, ligatures, diacritic placement, and bidirectional reordering. HarfBuzz does not render glyphs by itself; instead it outputs glyph indices and precise advances and offsets to be consumed by a renderer.

The engine relies on OpenType font data, using the font’s GSUB and GPOS tables to apply features. It supports a wide range of scripts, including Arabic, Hebrew, Indic scripts, Thai, Hangul, and many others, and handles script-specific shaping rules. It provides APIs for multiple platforms and can be integrated with font backends such as FreeType or platform text engines like CoreText and DirectWrite. It is used by many major projects and libraries, including web browsers, office suites, and text layout libraries such as Pango and Qt.

HarfBuzz is implemented in portable C and released as open-source software under permissive terms. Development is led by contributors from multiple organizations, with ongoing work to broaden script coverage, improve performance, and support additional font features and script shaping rules. The project emphasizes robust handling of complex text layouts and interoperability with other text-rendering components.