1810310 - All optional ligature features should be suppressed when non-zero letter-spacing is present

Status: RESOLVED FIXED

(Core :: Layout: Text and Fonts, defect, P3)

Description

[Jonathan Kew [:jfkthame]]

According to the CSS Fonts spec, item 11 in the list:

setting a non-default value for the letter-spacing property disables optional ligatures

Gecko has a longstanding implementation of this behavior, whereby non-zero letter-spacing disables the OpenType 'liga' (common ligatures) feature. However, it doesn't disable other kinds of "optional ligatures", in particular the features 'hlig' (historical ligatures) and 'dlig' (discretionary ligatures).

While the spec doesn't explicitly define what features "optional ligatures" should include, I think the intention must be that it means all ligature features other than 'rlig' "required ligatures". So 'dlig' and 'hlig' should be included in this.

We currently fail font-feature-resolution-002.html because of this.

Comment 1

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1810310 - When letter-spacing is present, disable all varieties of 'optional' ligatures, not only 'common' ones. r=#layout-reviewers

This fixes behavior on css/css-fonts/font-feature-resolution-002.html.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/6ccbc33d9c23
When letter-spacing is present, disable all varieties of 'optional' ligatures, not only 'common' ones. r=emilio

Comment 3

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/6ccbc33d9c23