1726314 - LCD subpixel rendering is inconsistently applied

Status: NEW

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

Description

[t.ambetarak]

Attachment: subpixel-rendering-screenshots.zip

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:90.0) Gecko/20100101 Firefox/90.0

Steps to reproduce:

My operating system (Arch Linux x86-64, up to date) is configured (via fontconfig) to render fonts using RGB subpixel rendering. Generally, Firefox does apply subpixel rendering, but this is inconsistent and exceptions seem to become more frequent with every release. Hence the bug report to draw attention to the issue. The issue applies to both the chrome and rendered web pages.

I have attached a zip archive with screenshots to illustrate the issue:

• ff-lcd-bug-bugzilla.png - Ironically, the issue is present when logging in to the Firefox bug tracker (e-mail address field content).
• ff-lcd-bug-gmail.png - All of GMail is rendered in grayscale.
• ff-lcd-bug-stackexchange.png - Stack Exchange is rendered in grayscale
• ff-lcd-bug-tabs.png - Chrome issue. The text on the tabs is rendered in grayscale. In comparison, text in the URL bar is rendered correctly using subpixel rendering.
• ff-lcd-bug-urlbar.png - If the text in the URL bar overflows the container, rendering reverts to grayscale here as well.
• ff-lcd-bug-urlbar-history.png - URL bar history is rendered in grayscale.
• ff-lcd-bug-grayscale-example.png - Zoomed in example of incorrect (grayscale) rendering
• ff-lcd-bug-bugzilla.png - Zoomed in example of correct (subpixel) rendering

I noticed there has been some recent work regarding subpixel rendering, but on the face of it, this patch only seems to constrict cases where subpixel rendering is used:

https://hg.mozilla.org/mozilla-central/file/tip/gfx/cairo/disable-subpixel-antialiasing.patch

Actual results:

Subpixel rendering, if configured in the OS via fontconfig, is applied inconsistently in both the chrome and rendered web pages.

Expected results:

Subpixel rendering should be applied consistently everywhere.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::Layout: Text and Fonts' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Comment 2

[Jim Mathies [:jimm]]

We're always working on improving support here. Thanks for the detailed report.

Comment 3

[Hanabishi]

Can confirm. Also I have found places where rendering type switches on the fly for unclear reasons.

Comment 4

[Hanabishi]

Attachment: font-render-issues.mp4

Comment 5

[Hanabishi]

Comment on attachment 9242934 [details]
font-render-issues.mp4

Very weird example. Look at the bottom text.

Comment 6

[Hanabishi]

Attachment: font-g.png

Closeup of the issue (grayscale)

Comment 7

[Hanabishi]

Attachment: font-s.png

Closeup of the issue (subpixel)