[MPEG-OTSPEC] WD for AMD 2 and COLR v1 enhancements

[Peter Constable]

In the past few weeks, I've been working with Rod Sheeter and Dominik Röttsches at Google to draft updates for the working draft related to COLR version 1. This fills out details for the new formats added in COLR version 1 as well as integrating with the existing text for COLR version 0 (which doesn't go away).

The proposed content for OFF Amendment 2 is available here:
https://github.com/googlefonts/colr-gradients-spec#annex-a-proposed-changes-to-isoiec-14496-22

When the COLR v1 enhancements were proposed here back in September, the proposal doc had specific details on the structure formats, but not much explanation of the semantics - how the formats represent different graphic concepts and are to be processed. Much of the additional content in this draft is conceptual explanation of the graphic operations that are supported and how the structures are used to represent those, with several figures to illustrate. The intent was not obvious before, but should be clear now with these additions.

There have also been some further design enhancements in the proposed draft: additional paint table formats for translate, rotate and skew transformations-the separate formats are more compact than the matrix format if only the specific transform is needed, and the rotate/skew formats specify rotation angles in degrees, which is much better when varying a rotation angle in a variable font than varying the matrix elements.

There are a few open issues ("TBD: ..." in that doc), but these are limited in scope and shouldn't hinder revision of the working draft considered by SC29 at the January meeting.

AHG members are invited to review and comment. I'd suggest that general comments not requiring specific action could be sent to this list, but for suggested improvement, it would be better to track these in GitHub issues-either in the GitHub repo above or in the MPEG/OFF repo:

Issues · MPEGGroup/OpenFontFormat (github.com)<https://github.com/MPEGGroup/OpenFontFormat/issues>


Re COLR v1 and OpenType: I've been preparing a parallel draft for the next OT version. That's in MSFT's typography repo, which is still a private repo. The content will differ from the OFF content only in minor, non-technical wording details.



Peter Constable
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