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# 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](https://www.princexml.com/), 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](https://github.com/n8willis/opentype-shaping-documents/),
which aims to specify OpenType font shaping behaviour.
## Features
* **Parse** TrueType (`ttf`), OpenType (`otf`), WOFF, and WOFF2 files.
* **Shape** Arabic, Latin, [Indic scripts](https://en.wikipedia.org/wiki/Languages_of_India)
(Bengali, Devanagari, Gujarati, Gurmukhi, Kannada, Malayalam, Oriya, Tamil, Telugu).
* **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](https://github.com/servo/pathfinder) or
[FreeType](https://www.freetype.org/) is responsible for rendering the glyphs.
To learn more about text rendering, Andrea Cognolato has a good [overview of
modern font rending on
Linux](https://mrandri19.github.io/2019/07/24/modern-text-rendering-linux-overview.html).
The concepts remain similar on other platforms.
## Examples/Getting Started
Refer to the [Allsorts Tools repository](https://github.com/yeslogic/allsorts-tools) for
a trio of tools that exercise Allsorts font parsing, shaping, and subsetting.
For shaping text the primary entry points are:
* [Font](font/struct.Font.html) — utility type that holds parsed font
tables, layout caches, etc. (we need to come up with a better name for it)
* [gsub::apply](gsub/fn.apply.html) — apply glyph substitution
* [gpos::gpos_apply](gpos/fn.gpos_apply.html) — apply glyph positioning
## Unimplemented Features / Known Issues
We don't currently support:
* Shaping Hebrew, Tibetan, and Mongolian.
* Apple's [morx table](https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6morx.html).
* Emoji.
* Unicode normalisation.
Known limitations:
* The crate is not well documented yet ([#5](https://github.com/yeslogic/allsorts/issues/5)).
* Allsorts does not do font lookup/matching. For this something like
[font-kit](https://github.com/pcwalton/font-kit) is recommended.
* The subsetting implementation is tailored towards PDF font embedding (mostly
the `cmap0` argument to
[the subset function](https://docs.rs/allsorts/latest/allsorts/subset/fn.subset.html))
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, [Fathom](https://github.com/yeslogic/fathom).
## 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](https://www.rust-lang.org/tools/install).
Build with `cargo build` and run the tests with `cargo test`.
## License
Allsorts is distributed under the terms of the Apache License (Version 2.0).
See [LICENSE](https://github.com/yeslogic/allsorts/blob/master/LICENSE) for details.