1509423 - Use harfbuzz for AAT layout instead of CoreText

Status: RESOLVED FIXED

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

Description

[Jeff Muizelaar [:jrmuizel]]

Now that harfbuzz supports AAT layout it seems like we should be able to drop support for shaping with CoreText.

Comment 1

[Jonathan Kew [:jfkthame]]

In principle, yes, though we should plan to do a fair bit of testing before we make that jump; this is very new (and not very extensively tested yet) on the harfbuzz side, so I don't want to rush things here.

Comment 2

[ebrahim]

Chrome is switched https://chromium-review.googlesource.com/c/chromium/src/+/1275945

Comment 3

[ebrahim]

Is it possible to see which tests needs to be rebaselined after the switch on Firefox also? That may help HarfBuzz development also.

Comment 4

[Jonathan Kew [:jfkthame]]

Attachment: Disable the gfxCoreText backend and use native HarfBuzz shaping for AAT fonts

Here's a patch to make us use harfbuzz native AAT support rather than Core Text for shaping; let's see how it fares on try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=a1311b6661a30c824554d387b4b300d07322e320.

Comment 5

[Jonathan Kew [:jfkthame]]

Attachment: Disable the gfxCoreText backend and use native HarfBuzz shaping for AAT fonts

Oops - the pref was set backwards in that patch, so the try push didn't really test anything... here goes, with the pref flipped so we'll really test the harfbuzz version. https://treeherder.mozilla.org/#/jobs?repo=try&revision=d983a399d6f17c2716ba49fce641cb41a43f5d48

Comment 6

[Jonathan Kew [:jfkthame]]

The test failures on try look pretty insignificant, but OTOH I've noticed a number of cases where the harfbuzz AAT support doesn't match Core Text rendering. Filed some issues upstream:

  https://github.com/harfbuzz/harfbuzz/issues/1528
  https://github.com/harfbuzz/harfbuzz/issues/1529
  https://github.com/harfbuzz/harfbuzz/issues/1530
  https://github.com/harfbuzz/harfbuzz/issues/1531
  https://github.com/harfbuzz/harfbuzz/issues/1532

We should probably see what happens with these before moving forward here.

Comment 7

[Jonathan Kew [:jfkthame]]

Attachment: Disable the gfxCoreText backend and use native HarfBuzz shaping for AAT fonts

Try run after harfbuzz 2.3.1 (bug 1524102) landed. The test failures look insignificant (typically tiny subpixel antialiasing issues), but there are still some Indic rendering issues with a few Apple fonts; e.g. the first line of the main text at https://www.unicode.org/standard/translations/telugu.html has a cluster that shapes incorrectly.

Comment 8

[Jonathan Kew [:jfkthame]]

I think we should go ahead and do this, once the mozilla-68 soft freeze period is past; it seems to be working OK for Chrome, AFAICT.

We can initially put the use of the old Core Text backend behind a pref, so that it's easy to revert to using it if we do see any issues, and then after it has baked for a couple of releases, we can pull out the old code altogether.

Comment 9

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1509423 - Disable the gfxCoreText backend and use native HarfBuzz shaping for AAT fonts. r=jrmuizel

Comment 10

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1509423 - Test/manifest updates to account for minor rendering differences between HarfBuzz and Core Text. r=jrmuizel

Depends on D31094

Comment 11

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/7bab77eee333
Disable the gfxCoreText backend and use native HarfBuzz shaping for AAT fonts. r=jrmuizel
https://hg.mozilla.org/integration/autoland/rev/6df30b02e311
Test/manifest updates to account for minor rendering differences between HarfBuzz and Core Text. r=jrmuizel

Comment 12

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Created web-platform-tests PR https://github.com/web-platform-tests/wpt/pull/16919 for changes under testing/web-platform/tests

Comment 13

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream web-platform-tests status checks passed, PR will merge once commit reaches central.

Comment 14

[Daniel Varga [:dvarga]]

https://hg.mozilla.org/mozilla-central/rev/7bab77eee333
https://hg.mozilla.org/mozilla-central/rev/6df30b02e311

Comment 15

[Web Platform Test Sync Bot [:wpt-sync] (Matrix: #interop:mozilla.org)]

Upstream PR merged