1726891 - font-feature-settings inline boundaries break contextual shaping

Status: UNCONFIRMED

(Core :: Layout: Text and Fonts, enhancement)

Description

[Myles C. Maxfield]

Attachment: feature-contextual-shaping.html

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.0 Safari/605.1.15

Steps to reproduce:

If there is an inline element boundary between two elements which use the same font, but differ only in their font-feature-settings, the contextual shaping across the inline element boundary will be broken. It isn't broken in Chrome.

See attached HTML file. Unfortunately, I don't think I have the rights to post the specific font used in this example, but any font which has both contextual shaping and font features should display the bug.

Comment 1

[Myles C. Maxfield]

Attachment: Firefox, Chrome, Safari

Comment 2

[Myles C. Maxfield]

I've filed the same bug on WebKit too: https://bugs.webkit.org/show_bug.cgi?id=229361

Comment 3

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Layout: Text and Fonts' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Comment 4

[Jonathan Kew [:jfkthame]]

Yes, currently text runs are always shaped with a single style (font, size, features, etc), and any change in these properties will interrupt shaping. Being able to change features (but not other properties) within the run without breaking shaping would be a nice enhancement (although it's a relatively niche use-case).