1533797 - downloadable font: not usable by platform

Status: VERIFIED FIXED

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

Description

[bmaupin]

Attachment: A screenshot of the broken bullet points

User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.121 Safari/537.36

Steps to reproduce:

Using Firefox in Linux, I opened a document in Microsoft Word Online that had bullet points.

Actual results:

The first and third levels of the bullet points were not properly rendered.

Expected results:

Word Online provides the missing fonts via CSS:

@font-face {
font-family: symbol;
src: url('https://fs.microsoft.com/fs/4.2/rawguids/26522609597');
}
@font-face {
font-family: Courier New_MSFontService;
src: url('https://fs.microsoft.com/fs/4.2/rawguids/38459451639');
}
@font-face {
font-family: Wingdings_MSFontService;
src: url('https://fs.microsoft.com/fs/4.2/rawguids/37798520877');
}

However, Firefox isn't able to load the fonts and the following errors appear in the console:

downloadable font: not usable by platform (font-family: "Wingdings_MSFontService" style:normal weight:400 stretch:100 src index:0) source: https://fs.microsoft.com/fs/4.2/rawguids/37798520877 unknown:15:17
downloadable font: not usable by platform (font-family: "symbol" style:normal weight:400 stretch:100 src index:0) source: https://fs.microsoft.com/fs/4.2/rawguids/26522609597

I've created a minimal test page here to reproduce the issue:

https://bmaupin.github.io/askubuntu-983191-research/test-bullet-points.html

More details on my research as well as a workaround are here:

https://github.com/bmaupin/askubuntu-983191-research#readme

Thanks!

Comment 1

[Lee Salzman [:lsalzman]]

Jonathan, any idea why it is failing to load these web fonts?

Comment 2

[Jonathan Kew [:jfkthame]]

Hmm, WFM on macOS, so it seems to be specific to the Linux backend. My guess is that it's because those fonts don't have a Unicode 'cmap' table, they're symbol-encoded. This probably causes them to fail when we call FT_Select_Charmap at https://searchfox.org/mozilla-central/rev/b9da45f63cb567244933c77b2c7e827a057d3f9b/gfx/thebes/gfxFcPlatformFontList.cpp#1991, which we do because we don't in general know how to handle random non-Unicode mappings in fonts.

I guess we could fall back to trying FT_ENCODING_MS_SYMBOL if we fail to find an FT_ENCODING_UNICODE mapping, and then this would probably work. We'd need to do that in a bunch of places where we currently just call FT_Select_Charmap(..., FT_ENCODING_UNICODE) and bail out on failure.

Comment 3

[Jonathan Kew [:jfkthame]]

Attachment: Bug 1533797 - Let freetype backend fall back to MS_SYMBOL if no UNICODE charmap is available. r=lsalzman

Comment 4

[Jonathan Kew [:jfkthame]]

I suspect something like this will probably resolve the problem; pushed it to try to check whether I broke anything. https://treeherder.mozilla.org/#/jobs?repo=try&revision=dbbdc571fbd9e7413bf9a38d8770ffc8bb887cad

I'll try to reproduce the issue and test the build later, and if all goes well we can consider it for review.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/ad447cf869e2
Let freetype backend fall back to MS_SYMBOL if no UNICODE charmap is available. r=lsalzman

Comment 6

[Daniel Varga [:dvarga]]

https://hg.mozilla.org/mozilla-central/rev/ad447cf869e2

Comment 7

[Alexandru Trif, Desktop QA [:atrif]]

Hello,
Reproduced the issue using Firefox 67.0a1 (20190308215337) on Ubuntu 18.04.
The issue is verified using Firefox 68.0b13 (20190624133534) and Firefox 69.0a1 (20190624213657) on Ubuntu 18.04.