Fontations

This repo contains a number of foundational crates for reading and manipulating OpenType font files. It is motivated by a desire to have more robust and performant open tools for a variety of font engineering and production tasks. For an overview of the motivations, see googlefonts/oxidize.

structure

Currently, this repo contains three main library crates: font-types, read-fonts, and write-fonts, in addition to one binary crate, otexplorer:

• font-types contains common definitions of the core types used in the OpenType spec. This is a small crate, and is intended as a basic dependency for any project reading or manipulating font data.
• read-fonts contains code for parsing and accessing font files. It is intended to be a high performance parser, suitable for shaping. In particular this means that it performs no allocation and no copying.
• write-fonts contains code for modifying and writing font data. It contains owned types representing the various tables and records in the specification, as well as code for compiling these and writing out font files. It has an optional dependency on read-fonts, in which case it can also parse font data, which can then be modified and written back out to disk.
• otexplorer is a binary crate for exploring the contents of font files. It is developed as a debugging tool, and may also be useful as an example of how the read-fonts crate can be used.

depgraph

Shows the non-dev dependency relationships among the font-related crates in fontations. fontc primarily uses the fontations crates via write-fonts and skrifa.

%% This is a map of non-dev font-related dependencies.
%% See https://mermaid.live/edit for a lightweight editing environment for
%% mermaid diagrams.

graph LR
    %% First we define the nodes and give them short descriptions.
    %% We group them into subgraphs by repo so that the visual layout
    %% maps to the source layout, as this is intended for contributors.
    %% https://github.com/googlefonts/fontations
    subgraph fontations[fontations repo]
        fauntlet[fauntlet\ncompares Skrifa & freetype]
        font-types[font-types\ndefinitions of types\nfrom OpenType and a bit more]
        read-fonts[read-fonts\nparses and reads OpenType fonts]
        skrifa[skrifa\nhigher level lib\nfor reading OpenType fonts]
        write-fonts[write-fonts\ncreates and edits font-files]
    end

    %% https://github.com/linebender/kurbo
    kurbo[kurbo\n2d curves lib]
    %% https://github.com/linebender/norad
    norad[norad\nhandles Unified Font Object files]
    %% https://github.com/PistonDevelopers/freetype-rs
    freetype-rs[freetype-rs\nbindings for the FreeType library]

    %% Now define the edges.
    %% Made by hand on March 20, 2024, probably not completely correct.
    %% Should be easy to automate if we want to, main thing is to
    %% define the crates of interest.
    fauntlet --> skrifa
    fauntlet --> freetype-rs
    read-fonts --> font-types
    skrifa --> read-fonts
    write-fonts --> font-types
    write-fonts --> read-fonts
    write-fonts --> kurbo
    norad --> kurbo

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codegen

Much of the code in the read-fonts and write-fonts crate is generated automatically. Code generation is performed by the font-codegen crate. For an overview of what we generate and how it works, see the codegen-tour. For an overview of how to use the font-codegen crate, see the readme at font-codegen/README.md.

Fuzzing

• Coverage can be viewed at https://oss-fuzz.com/, and search for "fontations"
• The fuzz/ crate in this repo contains our fuzzers
• fuzzers are implemented using the cargo-fuzz crate
• oss-fuzz configuration lives in https://github.com/google/oss-fuzz/tree/master/projects/fontations
  • build.sh looks for target/x86_64-unknown-linux-gnu/release/fuzz_*
  • ^ is meant to mean we can add additional fuzzers to fontations without having to touch oss-fuzz every time
  • build.sh also controls the test corpus, look for the git clone lines

To reproduce a fuzzer issue:

1. Download the file from the testcase, e.g. https://oss-fuzz.com/testcase-detail/6213391169945600
2. Build the fuzzers
   • cargo +nightly fuzz build -O --debug-assertions
3. Pass the repro file to the fuzzer
   • target/x86_64-unknown-linux-gnu/release/fuzz_skrifa_outline ~/Downloads/clusterfuzz-testcase-minimized-fuzz_skrifa_outline-6213391169945600

contributing

We have included a few git hooks that you may choose to use to ensure that patches will pass CI; these are in resources/githooks.

If you would like to have these run automatically when you commit or push changes, you can set this as your git hooksPath:

git config core.hooksPath "./resources/githooks"

note: If you wish to use the hooks on macOS, install the gnu coreutils (brew install coreutils, via homebrew.)

releasing

We use cargo-release to help guide the release process. It can be installed with cargo install cargo-release. You may need to install pkg-config via your package manager for this to work.

Releasing involves the following steps:

1. Determine which crates may need to be published: run cargo release changes to see which crates have been modified since their last release.

2. Determine the new versions for the crates.

   • Before 1.0, breaking changes bump the minor version number, and non-breaking changes modify the patch number.

3. Update manifest versions and release. ./resources/scripts/bump-version.sh orchestrates this process.

   • cargo release does all the heavy lifting

   # To see usage
   ./resources/scripts/bump-version.sh
   # To do the thing
   ./resources/scripts/bump-version.sh read-fonts write-fonts patch

4. Commit these changes to a new branch, get it approved and merged, and switch to the up-to-date main.

5. Publish the crates. ./resources/scripts/release.sh orchestrates the process.

   • You will be prompted to review changes along the way

   # To see usage
   ./resources/scripts/release.sh
   # To do the thing
   ./resources/scripts/release.sh read-fonts write-fonts

Skia and Chromium builds

An experimental SkTypeface implementation based on Fontations exists. This build is available in the Skia and Chromium repositories. The goal is to eventually use Fontations + Skia in Chromium as a memory-safe font backend. Tracking bugs: Skia, Chromium. To build the backends in Skia or Chromium follow the instructions below. This process is currently only tested on Linux.

Skia build

1. Download Skia https://skia.org/docs/user/download/, including bazelisk
2. $ bazelisk build --sandbox_base=/dev/shm --with_fontations //tools/viewer //tests:FontationsTest (to build debug, add -c dbg after build)
   • You should now have executables at bazel-bin/tests/FontationsTest and bazel-bin/tools/viewer/viewer

Skia Fontations unit tests

Build as above, then run the executable to run tests:

$ bazel-bin/tests/FontationsTest

OR compile and test in one command:

$ bazelisk test --sandbox_base=/dev/shm --with_fontations //tests:FontationsTest

Skia Fontations GM

Build as above then:

$ bazel-bin/tools/viewer/viewer --slide GM_typeface_fontations_roboto

OR build and run in one command:

$ bazelisk run --sandbox_base=/dev/shm --with_fontations //tools/viewer -- --slide GM_typeface_fontations_roboto

chromium build

1. Follow the instructions for getting and building Chromium
2. Add use_typeface_fontations = true to your args.gn using $ gn args out/<builddir>
3. Build Chromium using autoninja -C out/<builddir> chrome
4. Run Chromium using $ out/<builddir>/chrome
5. Go to chrome://flags/#enable-fontations-backend and activate the flag, restart Chrome.
6. Navigate to any URL, observe web fonts being displayed with Fontations + Skia path rendering.