1462287 - @font-face: The font is different with gfx.downloadable_fonts.validate_variation_tables set on False

Status: RESOLVED INVALID

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

Description

[roxleitan]

Attachment: font.png

Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:62.0) Gecko/20100101 Firefox/62.0
Build ID: 20180516220130

[Affected versions]:
Nightly 62.0a1

[Affected platforms]:
Windows 10 x64

[Prerequisites]:
Set pref gfx.downloadable_fonts.otl_validation = false

Steps to reproduce]:
1.Launch Nightly 62.0a1 with a new profile
2.Open https://bug1451327.bmoattachments.org/attachment.cgi?id=8970158

[Expected result]:
The font should be displayed as in Chrome and MSEdge and as without changing the pref "gfx.downloadable_fonts.validate_variation_tables"

[Actual result]:
The page is displayed with different font

Comment 1

[Jonathan Kew [:jfkthame]]

It's expected that some fonts may be handled differently if that pref is changed.

This font has an OpenType GDEF table that includes variation-font extensions; validating this requires that variation-table validation is enabled. If the gfx.downloadable_fonts.validate_variation_tables pref is turned off, then the GDEF table will fail validation and the font is rejected.

This wouldn't affect a release build, because for release channels we bypass validation of the OpenType layout tables; you can confirm this configuration by setting gfx.downloadable_fonts.otl_validation to false; then the font will load successfully regardless of the setting of gfx.downloadable_fonts.validate_variation_tables.

So the font loads successfully if:

  gfx.downloadable_fonts.validate_variation_tables = true
  gfx.downloadable_fonts.otl_validation = either true or false

(note that the defaults on Nightly/Developer builds are true/true),

and also loads successfully if:

  gfx.downloadable_fonts.validate_variation_tables = true
  gfx.downloadable_fonts.otl_validation = false

(which will be the default prefs on release channels),

but it fails to load (with error messages logged to the Web Console) if:

  gfx.downloadable_fonts.validate_variation_tables = false
  gfx.downloadable_fonts.otl_validation = true

Comment 2

[Jonathan Kew [:jfkthame]]

Sorry, I didn't mean to mark this FIXED; rather, I think it is INVALID because this is a non-standard prefs setting, and it is having the expected effect. So it's not a bug in the behavior.