1424648 - Helvetica Bold drawn with non-bold glyphs

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, defect, P2)

Description

[Jan Alexander Steffens [:heftig]]

Setup:
Nightly on Arch Linux
WebRender enabled
Helvetica.ttc sourced from MacOS High Sierra

Helvetica Bold is drawn using metrics from the bold variant but with glyphs from the normal variant. Perhaps a glyph caching issue?

Non-WebRender is fine.

Comment 1

[Milan Sreckovic [:milan] (needinfo for best results)]

Linux only?

Comment 2

[Jan Alexander Steffens [:heftig]]

I can only test Linux, I'm afraid.

Comment 3

[Jan Alexander Steffens [:heftig]]

There's a related problem where Helvetica Light picks the wrong glyphs and the string "abcdefgh" is drawn as "_`abcdef" with the Regular outlines but the correct metrics. E.g. the "f" has the Regular "d" outline but the Light "f" metrics.

I think WebRender might be losing the face index needed to go with the font file somewhere.

FontHandleMethods::new_from_template (servo/components/gfx/platform/freetype/font.rs) looks like it loads font data from a FontTemplateData, which holds a read font file, but the FontTemplateData only uses the pathname as its identifier and create_face_from_buffer always uses 0 as the face index.

Comment 4

[Jan Alexander Steffens [:heftig]]

for_each_variation (servo/components/gfx/platform/freetype/font_list.rs) also drops the font index on the floor.

Comment 5

[Jan Alexander Steffens [:heftig]]

Attachment: fix-ttc.diff

The attached patch seems to fix things and renders all 6 of Helvetica's styles properly. That said I was flying blind and don't even know what (WR)FontDescriptorOutput is for.

Perhaps some clarification before I can pack this up in a reviewable patch with a proper message?

Comment 6

[Jan Alexander Steffens [:heftig]]

Attachment: Bug 1424648 - Provide proper face index to FreeType FontDescriptorOutput;

OpenType font collections (*.ttc) contain multiple faces in a single file,
identified via index. When creating a font descriptor for a FreeType or
Fontconfig font, we mistakenly set the index to zero, always.

This bug became visible when layout and WebRender would disagree on the face in
use, rendering text with the metrics from the proper face but the outlines of
another. Unless, of course, the selected face was the first (or only) in the
font file.

Review commit: https://reviewboard.mozilla.org/r/216978/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/216978/

Comment 7

[Lee Salzman [:lsalzman]]

Comment on attachment 8947221 [details]
Bug 1424648 - Provide proper face index to FreeType FontDescriptorOutput;

https://reviewboard.mozilla.org/r/216978/#review222830

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/b8ad646de7a7
Provide proper face index to FreeType FontDescriptorOutput; r=lsalzman

Comment 9

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/b8ad646de7a7