1759988 - Characters in private use areas should not fallback to system fonts

Status: RESOLVED FIXED

(Core :: Graphics: Text, enhancement)

Description

[Xidorn Quan [:xidorn] UTC+10]

Attachment: screenshot

Steps to reproduce:

• open a page with PUA characters but no font covers, e.g. https://en.wikipedia.org/wiki/Medieval_Unicode_Font_Initiative#Private_Use_Area

Expected behavior:
The PUA characters should be rendered as unknown characters

Actual behavior:
They fallback to system fonts, see the screenshot, the characters fallback to "AR PL UKai HK" on my system.

I found bug 399369 which seems to indicate that font fallback should have been disabled, but I found no bug explicitly reverting that decision, so maybe something went wrong?

Comment 1

[Jonathan Kew [:jfkthame]]

Yeah, this seems wrong. My first thought was that it's fontconfig doing something weird, but then I loaded the example wikipedia page in my Nightly on macOS and saw the same issue. So looks like it's a generic issue, not platform-specific.

But after letting Nightly update & restart itself, it's not reproducing for me any more; I just get hexboxes for the characters where I don't have one of the explicitly-named PUA fonts installed.

Not sure why it's behaving inconsistently for me... I'll try other systems and see whether it shows up again.

Comment 2

[Xidorn Quan [:xidorn] UTC+10]

I can see it inconsistent on Nightly as well.

It seems that if I open it right after starting Nightly, it correctly shows hexboxes. but if I open a new tab to open the page again, the characters show up.

Comment 3

[Jonathan Kew [:jfkthame]]

I've pushed a try job with a patch that I believe will fix this at https://treeherder.mozilla.org/jobs?repo=try&revision=c6cb6544a77ffb986d8ff5e3e4e17e2e5039809f. If you have a chance to try a build from there and confirm if it resolves the problem, that'd be great - thanks!

Comment 4

[Xidorn Quan [:xidorn] UTC+10]

That build seems to fix the issue here. Thanks!

Comment 5

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1759988 - Ensure InitializeCodepointsWithNoFonts() is always called during font-list initialization. r=#gfx-reviewers

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/5247739359f7
Ensure InitializeCodepointsWithNoFonts() is always called during font-list initialization. r=gfx-reviewers,jrmuizel

Comment 7

[Iulian Moraru]

https://hg.mozilla.org/mozilla-central/rev/5247739359f7