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.
- Parse TrueType (
ttf), OpenType (
otf), WOFF, and WOFF2 files.
- Shape Arabic, Latin, Indic scripts (Bengali, Devanagari, Gujarati, Gurmukhi, Kannada, Malayalam, Oriya, Tamil, Telugu).
- Subset from TrueType, OpenType, WOFF, and WOFF2 files into OpenType.
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.
Refer to the Allsorts Tools repository for a trio of tools that exercise Allsorts font parsing, shaping, and subsetting.
For shaping text the primary entry points are:
- Font — utility type that holds parsed font tables, layout caches, etc. (we need to come up with a better name for it)
- gsub::apply — apply glyph substitution
- gpos::gpos_apply — apply glyph positioning
We don’t currently support:
- Shaping Hebrew, Tibetan, and Mongolian.
- Apple’s morx table.
- Unicode normalisation.
- 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
cmap0argument to the subset function) at the moment.
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, Fathom.
Allsorts CI runs tests on Linux, macOS, and Windows. Via Prince it is also built for FreeBSD.
Minimum Supported Rust Version: 1.38.0
To build the crate ensure you have Rust 1.38.0 or newer installed.
cargo build and run the tests with
Allsorts is distributed under the terms of the Apache License (Version 2.0).
See LICENSE for details.
Reading and writing of binary data.
Bitmap font handling.
CFF font handling.
Checksum calculation routines.
Utilities for performing contextual lookup in gpos and gsub.
Top-level font file representation.
Utilities for obtaining a name from a fonts
Utilities for accessing glyph information such as advance.
Glyph positioning (
Glyph substitution (
Utilities for handling the Mac OS Roman character set.
Definitions of the sizes of binary types.
OpenType font table parsing and writing.
Utilities and constants for OpenType tags.
Reading of the WOFF font format.
Reading of the WOFF2 font format.
Generate a 4-byte OpenType tag from byte string