Gradient Color Fonts, COLR v1 Contributions to FreeType

[Dominik Röttsches]

Hi,

In a team effort with Roderick Sheeter & Cosimo Lupo & Dave Crossland
(Google Fonts) and myself (Blink/Chrome) we have proposed and
published an OpenType extension to the COLR table to bring color
gradients to color vector fonts.

You can find the proposal here:
https://github.com/googlefonts/colr-gradients-spec/blob/master/colr-gradients-spec.md

Initial test/prototype fonts have been published here:
https://github.com/googlefonts/color-fonts

The proposal is an incremental, backwards compatible extension to the
COLR table and brings gradients to color fonts while enabling support
for OpenType variations on all aspects of the gradient definitions.

I've started prototyping support for the COLR v1 additions to FreeType
in a local repository. Once I am making further progress, I would like
to share a proposal for API additions to FreeType in the section
that's described as "Glyph Layer Management" in the API docs for
review. Initially, the main focus would be to expose gradient
information in a way similar to an extended FT_Get_Color_Glyph_Layer
method, so that the gradient specifications can be extracted and
painted at higher levels, for example in our Skia graphics library.

Once I have something to present, I'd be happy if FreeType maintainers
and reviewers could take a look and ensure it fits FreeType's
conventions and existing style, and decide if such contributions could
be merged to the FreeType project.

If you have any questions on COLR v1, I'll try to answer those and I'd
be happy to hear any thoughts and feedback so far,

Dominik