1455265 - Elements with writing-mode:tb-rl don't display ZWJ Emoji sequences expectedly

Status: RESOLVED FIXED

(Core :: Graphics: Text, defect, P3)

Description

[kei.itof]

Attachment: vertical-emoji.gif

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36

Steps to reproduce:

1. Visit https://codepen.io/wemotter/pen/MGYmKy
2. Click the "toggle vertical" button


Actual results:

Each emoji sequences are displayed as multiple characters.


Expected results:

They should look like one character.

Comment 1

[Rares Doghi, Desktop QA]

Hello, i can reproduce this issue on Firefox 59.0.2 as well as 61.0a1 (2018-04-24) using Mac OS X (10.12.6).

Comment 2

[Jonathan Kew [:jfkthame]]

This is because the Apple Color Emoji font depends on AAT shaping (ligatures implemented in the 'morx' table) to create these glyphs from the underlying sequences; but in vertical mode, we always shape through harfbuzz, which doesn't currently (in the version we have in-tree) implement AAT features. We do this because our Core Text back-end doesn't support vertical shaping.

So this may well be fixed - or at least should be re-tested - once we've updated to a harfbuzz release that includes AAT support. That may be all it takes to make this work as expected.

Comment 3

[Jonathan Kew [:jfkthame]]

AFAICS this is now fixed: the testcase (https://codepen.io/wemotter/pen/MGYmKy) works in Nightly now that bug 1500356 has landed.