raqm

Raqm is an open-source text shaping library designed to provide complex text layout for scripts that require bidirectional processing and contextual glyph shaping, such as Arabic and other bi-directional languages. It functions as a higher-level shaping engine that can be integrated into rendering pipelines to produce sequences of positioned glyphs suitable for display.

The library is implemented in C and exposes an API that takes Unicode text and font information as input and outputs an ordered sequence of glyph indices with their corresponding positions. This enables downstream rendering components to render scripts that involve ligatures, contextual forms, and right-to-left and left-to-right mixing in a consistent manner.

Raqm relies on established low-level components to perform its work. It typically uses a bidirectional algorithm library to determine the correct visual ordering of characters and a shaping engine to convert characters into glyphs, including any necessary ligatures and diacritics. It is commonly used in conjunction with font rendering toolchains such as FreeType and HarfBuzz, as well as other Unicode-aware libraries, to handle the complexities of script shaping across different languages.

Development and usage notes: RAQM is maintained by a community of contributors and is used in various open-source projects that require robust complex text layout. It aims to provide a practical, portable solution for rendering languages that depend on sophisticated shaping rules beyond simple character rendering.

See also: HarfBuzz, FriBidi, FreeType, Unicode, complex text layout.