Intent to prototype: COLRv1 (enhanced color font format) support

[Jonathan Kew]

Summary:

COLRv1 is a new format for full-color OpenType fonts, building on the
original COLR (v0) format for simple colored layers and providing a
richer graphic model including gradients and transformations.

This format provides font designers with graphic expressiveness
comparable to SVG-in-OpenType, but with a much more concise and
efficient representation; it also provides new flexibility via the use
of OpenType variations to dynamically modify the glyphs.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1740525

Specification:

- https://docs.microsoft.com/en-gb/typography/opentype/spec/colr
- https://github.com/googlefonts/colr-gradients-spec

Standards Body:

Part of the OpenType (Microsoft) / Open Font Format (ISO SC29/WG3) specs.

Platform coverage: All

Preference: gfx.font_rendering.colr_v1.enabled

DevTools bug: n/a

Other browsers:

- Blink: partial implementation (without variations support) shipping;
full implementation behind "Variable COLRv1 Fonts" flag in Canary.

- WebKit: no current plans AFAIK

web-platform-tests:

Not yet in place; experimental fonts for interoperability testing are
being created at https://github.com/googlefonts/color-fonts, and I
expect in due course an agreed test suite will emerge (though
interoperably testing the precise rendering of complex graphic
compositions is tricky...)

As an interim measure, I propose to include some basic reftests in our
tree, per https://phabricator.services.mozilla.com/D154586.


- Jonathan

[Tom Ritter]

It looks like OTS does not support sanity-checking COLR[0] so I am curious if we have fuzz coverage for this feature?

-tom

[0] https://github.com/khaledhosny/ots/issues/202

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[Christian Holler]

We've looked into this and Tyson pointed out to me that freetype2 has fuzz coverage for this feature on oss-fuzz:

https://github.com/freetype/freetype2-testing/tree/master/fuzzing#colrv1-methods

If there is other code we should look at, please let us know.

- Chris

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[Jonathan Kew]

On 15/08/2022 18:21, Tom Ritter wrote:
> It looks like OTS does not support sanity-checking COLR[0] so I am
> curious if we have fuzz coverage for this feature?
>

Not yet (at least not to my knowledge); it'd be good to get started on that.

Also, I am intending to look at adding COLR support to OTS, as an
element of defence-in-depth here.

JK


> -tom
>
> [0] https://github.com/khaledhosny/ots/issues/202

> <https://github.com/googlefonts/color-fonts>, and I

> expect in due course an agreed test suite will emerge (though
> interoperably testing the precise rendering of complex graphic
> compositions is tricky...)
>
> As an interim measure, I propose to include some basic reftests in our
> tree, per https://phabricator.services.mozilla.com/D154586

> <https://phabricator.services.mozilla.com/D154586>.

>
>
> - Jonathan
>
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[Jonathan Kew]

On 15/08/2022 18:24, Christian Holler wrote:
> We've looked into this and Tyson pointed out to me that freetype2 has
> fuzz coverage for this feature on oss-fuzz:
>
>
https://github.com/freetype/freetype2-testing/tree/master/fuzzing#colrv1-methods
>
> If there is other code we should look at, please let us know.
>
> - Chris

We're not using freetype2's implementation (as we don't have freetype in
Gecko at all on Windows or macOS).

So in bug 1740530 there'll be new code landing (in
gfx/thebes/COLRFonts.{h,cpp}) to handle the COLR table; it'd be good to
have our fuzzers poking at that before it heads to release. (Initial
landing will be behind a pref, enabled by default only on Nightly.)

JK

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