Crate allsorts

Expand description

Font parser, shaping engine, and subsetter

Allsorts is a font parser, shaping engine, and subsetter for OpenType, WOFF, and WOFF2 written entirely in Rust. It was extracted from Prince, a tool that typesets and lays out HTML and CSS documents into PDF.

The Allsorts shaping engine was developed in conjunction with a specification for OpenType shaping, which aims to specify OpenType font shaping behaviour.

Features

Parse TrueType (ttf), OpenType (otf), WOFF, and WOFF2 files.
Shape Arabic, Cyrillic, Greek, Hebrew, Indic scripts (Bengali, Devanagari, Gujarati, Gurmukhi, Kannada, Malayalam, Oriya, Sinhala, Tamil, Telugu), Khmer, Lao, Latin, Syriac, Thai, and other scripts.
Subset from TrueType, OpenType, WOFF, and WOFF2 files into OpenType.

What is font shaping?

Font shaping is the process of taking text in the form of Unicode codepoints and a font, and laying out glyphs from the font according to the text. This involves honouring kerning, ligatures, and substitutions specified by the font. For some languages this is relatively straightforward. For others, such as Indic scripts it is quite complex. After shaping, another library such as Pathfinder or FreeType is responsible for rendering the glyphs. To learn more about text rendering, Andrea Cognolato has a good overview of modern font rending on Linux. The concepts remain similar on other platforms.

Examples

Refer to the Allsorts Tools repository for a set of tools that exercise Allsorts font parsing, shaping, and subsetting.

Unimplemented Features / Known Issues

We don’t currently support:

Shaping Mongolian, and Tibetan.
Apple’s morx table.
Unicode normalisation.

Known limitations:

The crate is not extensively documented yet (#5).
Allsorts does not do font lookup/matching. For this something like font-kit is recommended.

Build with cargo build and run the tests with cargo test.

Cargo Features

Feature	Description	Default Enabled	Extra Dependencies
`outline`	Enable code for accessing glyph outlines	✅	`pathfinder_geometry`
`flate2_zlib`	Use the zlib backend to flate2	✅	`zlib`
`flate2_rust`	Use the Rust backend to flate2	❌	`miniz_oxide`
`prince`	Enable Prince specific tests and code	❌

Note: In our testing the zlib flate2 backend was faster but you may prefer the Rust backend for a pure Rust solution when compiling to WASM or similar.

Contributing

Contributions are welcome, please refer to the contributing document for more details.

Code of Conduct

We aim to uphold the Rust community standards:

We are committed to providing a friendly, safe and welcoming environment for all, regardless of gender, sexual orientation, disability, ethnicity, religion, or similar personal characteristic.

We follow the Rust code of conduct.

Acknowledgements

OpenType shaping documents forms the specification from which the shaping engine is implemented.
HarfBuzz the widely used open source font shaping engine was used as reference for test output.
The Adobe Annotated OpenType Specification test suite is used as part of the Allsorts test suite.
ttf-parser for CFF CharString parsing code.