[MPEG-OTSPEC] OpenType 1.9.1 Beta review

Peter Constable pconstable at microsoft.com
Thu May 16 03:39:46 CEST 2024

After (very unfortunately) being delayed by over a year, the next version of the OpenType Spec, OpenType 1.9.1, has progressed from Alpha to Beta.

OpenType 1.9.1 Beta Review - Typography | Microsoft Learn<https://learn.microsoft.com/en-us/typography/opentype/otspec191/ot191beta>

The Beta review period is planned to be fairly short before the new version is finalized and released. This shouldn't be a concern since most of the content has been available as alpha for a long time, and most or all changes have also been submitted to MPEG and incorporated into either Amd 2 of the 4th edition or the WD for the 5th edition.

The most significant technical change is a change in the interpretation of COLRv1 sweep gradient data. This was already incorporated into Amd 2, and was originally intended to be the main focus for v1.9.1, until (i) events led to a delay and then (ii) it became a priority to get changes from OT 1.8.4 and OT 1.9 incorporated into the WD for OFF 5th edn.

The next most significant change is the complete, editorial re-write of the CFF2 and CFF2 CharString specs (now combined into a single chapter) that is being incorporated into the 5th edn CD. (A draft was already incorporated into earlier WD revisions, and my contribution to MPEG last month included further editorial updates.)

For those interested to see in detail what has changed in OT 1.9.1, there are "delta" pages that include change tracking. Note, though, that some chapters have had a lot of editorial revision, so on some pages it may be hard to "see the trees for the forest". See the change log<https://learn.microsoft.com/en-us/typography/opentype/otspec191/changes> (or the "delta" pages) for more information on changes. The Beta Review landing page also provides links to issue reports that were addressed in this update.

Note that OT 1.9.1 does _not_ include the new extensions (wide glyph IDs, VARC...) that have been under discussion for OFF 5th edn. The scope for OT 1.9.1 was intended to be limited to only the COLRv1 update, the CFF2 re-write, editorial sync with OFF, and those fixes for reported issues that could be fit in along the way.

Peter Constable
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