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

Mon Jan 4 22:33:03 CET 2021

Dear all,

Happy New Year! I hope you had a nice holiday break.

Please see attached for your review two input contributions I prepared based on the input to this AHG (and public GitHub discussions) on behalf of their respective authors. Since I did not receive any additional comments, I intend to submit these contributions to WG document registry by end of day today. 

Please also note that the contribution m55831 [summarizing COLR v1 updates] includes a number of highlighted unresolved topics that will need to be discussed as part of the break-out group session during the week of the WG meeting (Jan. 11-15, 2021). We need to finalize them by Jan. 15 if we plan to recommend the promotion of the current Working Draft amendment to the next Committee Draft stage.

Thank you all for your contributions,

Vladimir

From: Vladimir Levantovsky [mailto:vladimir.levantovsky at gmail.com] 
Sent: Sunday, December 27, 2020 1:59 PM
To: Peter Constable <pgcon6 at msn.com>
Cc: MPEG OT Spec list (mpeg-otspec at lists.aau.at) <mpeg-otspec at lists.aau.at>
Subject: Re: [MPEG-OTSPEC] WD for AMD 2 and COLR v1 enhancements

Hello all,

Many thanks to Peter, Rod, Dominik, and many other people who have contributed their review comments to the development and improvements of the proposed text for COLR v1 amendment.

Since the deadlines for registration and upload of input contributions is coming up soon, I would like to propose the following plan of actions:

- use the updated COLR v1 text from the public GitHub repo https://github.com/googlefonts/colr-gradients-spec#annex-a-proposed-changes-to-isoiec-14496-22 as the basis for the updated proposal;

- extend the current draft amendment with three additional amended parts proposed as part of MPEGGroup/OpenFontFormat  <https://github.com/MPEGGroup/OpenFontFormat/issues> discussions (issues 36-38);

- submit the AHG Recommendation to consider the proposed changes be used as a replacement to the current content of the Working Draft ISO/IEC 14496-22/AMD2.

Please submit your additional comments and proposed changes (if any) no later than the end of day on December 30. In absence of additional comments, and if no objections will have been raised by Dec. 30 - I will consider the current text of the proposal, along with the additional changes, to be approved by AHG consensus.

Thank you again for your contributions!

Vladimir

On Tue, Dec 22, 2020 at 10:00 PM Peter Constable <pgcon6 at msn.com <mailto:pgcon6 at msn.com> > wrote:

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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