[Webkit-unassigned] [Bug 112488] REGRESSION (r145854): Mongolian characters are not upright in vertical writing mode

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=112488

--- Comment #65 from Koji Ishii <kojiishi at gmail.com> ---
(In reply to comment #54)
> The exclusion from
> rotation based on UTR#50 is correct, but the code in the complex text
> drawing path fails to handle correctly the case of fonts with vertical
> glyphs.

Sorry for very very late follow-up, but I'm sorry to say that you misunderstood UTR#50. In short, Mogolian and Phags-Pa should be excluded from rotation, even if their fonts have vertical glyphs. I haven't looked at the details of the patch, but the approach is correct.

A long version. Up to rev. 10 of UTR#50, Mongolian and Phags-Pa were U, just because UTR#50 is defined against characters in the Unicode code charts, and these characters in the code charts are pre-rotated, so U means that "render as in the code charts."

The Unicode Technical Committee was aware of that almost every single font in the wild are pre-rotated, and therefore implementers must interpret U in the table to be R for Mongolian and Phags-Pa, but because fonts being pre-rotated is not defined in Unicode, and because code charts were already there, we hoped implementers read it correctly.

After revision 10 was published, we found that we were too optimistic. One implementer, WebKit, implemented Mongolian and Phags-Pa as U. By that time, we had a luck to update the Unicode Standard, so we changed the orientation of these characters in the code charts and updated UTR#50 to R.

Hope this makes sense.

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