Allsorts

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, Tamil, Telugu), Latin, Syriac, 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 trio of tools that exercise Allsorts font parsing, shaping, and subsetting.

Unimplemented Features / Known Issues

We don't currently support:

• Shaping Khmer, Mongolian, Sinhala, and Tibetan.
• Apple's morx table.
• Unicode normalisation.

Known limitations:

• The crate is not well documented yet (#5).
• Allsorts does not do font lookup/matching. For this something like font-kit is recommended.
• The subsetting implementation is tailored towards PDF font embedding (mostly the cmap0 argument to the subset function) at the moment.

Development Status

Allsorts is still under active development but has reached its first release milestone with its inclusion in Prince 13. In Prince it is responsible for all font loading, and font shaping.

Currently the font parsing code is handwritten. It is planned for this to eventually be replaced by machine generated code via our declarative data definition language project.

Platform Support

Allsorts CI runs tests on Linux, macOS, and Windows. Via Prince it is also built for FreeBSD.

Building and Testing

Minimum Supported Rust Version: 1.38.0

To build the crate ensure you have Rust 1.38.0 or newer installed.

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

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.

License

Allsorts is distributed under the terms of the Apache License (Version 2.0).

See LICENSE for details.