Hackathon: Browser integration of Fontations Rust font stack

[drott]

Logistics

• Date & Time: Tuesday 3rd June at 10:00 CEST (local time)
• URL: https://meet.jit.si/WEH2025-Fontations
• Notes: https://github.com/Igalia/webengineshackfest/wiki/2025-Hackathon:-Browser-integration-of-Fontations-Rust-font-stack
• Room: CSS

Facilitator(s)

@drott

Summary

In Chrome we've started to ship the new open-source Rust font stack based on Fontations and Skia. I volunteer to host a hackathon to experiment with integration of Fontations into Servo and Firefox and consult with build system integration, foreign-function-interface design and API questions on Fontations.

Potential initial milestones:

• Servo: Integrate Fontations to perform font metrics parsing, COLRv0/COLRv1 support? Other?
• Firefox: Introduce Fontations dependency, metrics parsing COLRv0/COLRv1 support? Other?

@mrobinson and @jfkthame have expressed interest from the Servo and Mozilla side respectively.

Type

Onsite

Other comments

I suggest for the length of this breakout session to be a longer session and for it to extend over the time of the event - availability of the participants permitting.

[drott]

CC @foolip

[drott]

CC @delan

[nicoburns]

A Fontations (Skrifa) backend for WebRender (specifically wr_glyph_rasterizer) would be cool (and could be used by both Servo and Firefox). There is a fork of WebRender (https://github.com/declantsien/webrender/tree/emacs) that implements a Swash backend (https://github.com/declantsien/webrender/blob/emacs/wr_glyph_rasterizer/src/backend/swash/font.rs) (Skrifa being originally derived from Swash) which could likely be adapted.

There is one significant difference between Swash and Skrifa which is that Swash includes a vector rasterizer (based on Zeno) whereas Skrifa does Scaling/Hinting but leaves the rasterizeration to the caller. So a Skrifa backend for WebRender would need to combine Skrifa with a general purpose vector renderer such as Skia or Tiny-Skia.

I think Firefox already bundles Skia? So Skia might make sense there.

Servo doesn't so something "smaller and lighter" like Tiny-Skia would probably make sense. Tiny-Skia supports most of the necessary graphics operations, but is missing support for "sweep gradients" (aka conic gradients) which are needed for COLRv1 (porting those from Skia would potentially be fun smallish project in and of itself)

[drott]

@nicoburns I am not super familiar with the web render capabilities: Does webrender itself contain a bezier curve rasterizer? Is it capable of rendering most of SVG on its own? If it can render curves, could webrender itself be used to render glyphs from paths?

Skrifa does provide glyph contours in OutlineGlyph::draw which could then be connected.

[nicoburns]

@nicoburns I am not super familiar with the web render capabilities: Does webrender itself contain a bezier curve rasterizer? Is it capable of rendering most of SVG on its own? If it can render curves, could webrender itself be used to render glyphs from paths?

@drott My understanding is that WebRender does not do vector rendering at all. I believe Firefox uses Moz2D for this. Servo only really supports vector rendering for Canvas2D for which is currently uses raqote (but raqote is both slow and unmaintained, so it is not seen as long term solution and I suspect it would be better to bring in something else rather than use raqote).

[drott]

Small logistics update:

Matrix

• https://matrix.to/#/#fontationshackathon:matrix.org

Space/Location

For the hackathon, we'll use one of the open hacking spaces during the conference (example: @mrego provided this photo from a previous event). Depending on which talks people want to attend on the first day, we can then figure out in the first break what's the best first time slot of attendees to get together and organize a bit on what we want to focus on.

Announcements / Breakout session

• In the conference opening talk, I'll introduce the workshop briefly (few minutes), and we'll decide on the space where we can meet.

• Then on Tuesday morning of the conference, there'll be a breakout session on the Fontations hackathon.

Planning / Goalsetting

Please start tossing around and contributing ideas below for where we could take the integration of Fontations into other engines.

Firefox hacking

@jfkthame For hacking on Firefox, what do you think could be the goals for the hackfest? Are there subcomponents with tests of Firefox that can be built and into which we could hack

Font metadata parsing in Servo

@mrobinson IIRC you mentioned, reading metrics or names or other font metadata in servo could be a good starting point. Would you have a pointer to the code in that area?

Rendering in Servo (?)

@nicoburns Is it so that you're working on a CPU backend for vello? (IIUC I heard something along those lines from @dfrg) - is this something that you were interested in experimentally integrating?

Build Instructions

• Firefox build instructions: https://firefox-source-docs.mozilla.org/setup/linux_build.html#system-preparation
• Servo Build Instructions: https://book.servo.org/hacking/building-servo.html

Fontations Docs

• Skrifa (higher level processing): https://docs.rs/skrifa/latest/skrifa/
• Read-fonts https://docs.rs/read-fonts/latest/read_fonts/
• Font-types https://docs.rs/font-types/latest/font_types/

Chromium Fontations Bindings Code in Skia

• https://source.chromium.org/chromium/chromium/src/+/main:third_party/skia/src/ports/fontations/src/ffi.rs

[jfkthame]

@jfkthame For hacking on Firefox, what do you think could be the goals for the hackfest? Are there subcomponents with tests of Firefox that can be built and into which we could hack

I'd be interested in exploring the possibility of replacing the freetype-based code we use on Linux & Android to load font tables, read metrics, etc. Unfortunately I don't think there are relevant subcomponents that can readily be built and tested separately from the full Firefox build; we don't have a standalone build of a font-management component or similar. :-(

[drott]

I'd be interested in exploring the possibility of replacing the freetype-based code we use on Linux & Android to load font tables, read metrics, etc. Unfortunately I don't think there are relevant subcomponents that can readily be built and tested separately from the full Firefox build; we don't have a standalone build of a font-management component or similar. :-(

Thanks, sounds great for a hackathon goal. I followed build instructions on a beefy workstation, and noticed that finished rather quickly, so the full build seems fine here.

[mrego]

We're proposing Tuesday 3rd June at 10:00 CEST (local time) for this session.

If that's a problem, please let us know to try to find other slot in the scheduling.

[nicoburns]

@nicoburns Is it so that you're working on a CPU backend for vello? (IIUC I heard something along those lines from cbrokaw) - is this something that you were interested in experimentally integrating?

I haven't been working on vello_cpu itself except for a couple of minor fixes (credit there goes to @LaurenzV), but I am interested in combining it with skrifa to create a pure-rust glyph rasterization backend for WebRender.

Regarding font-metric parsing:

• The relevant code in Servo is mostly here: https://github.com/servo/servo/blob/main/components/fonts/platform/freetype/font.rs
• I have some Skrifa-based metrics parsing code that I wrote for Blitz and could be used as reference here: https://github.com/DioxusLabs/blitz/pull/204/files#diff-6d5769ad47a07867d77712b6dd6f7e3c669924353d4796f8e515eeaf6faa7df9R61

P.S. I think you meant to tag @dfrg. "cbrokaw" does not seem to be the same person as far as I can tell.

[mrego]

Notes at https://github.com/Igalia/webengineshackfest/wiki/2025-Hackathon:-Browser-integration-of-Fontations-Rust-font-stack