1790564 - Prevent Anti-Aliasing of Embedded Bitmap Fonts on Linux

Status: UNCONFIRMED

(Core :: Graphics: Text, defect)

Description

[Zhang Boyang]

Attachment: firefox104.0.2_normal.png

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Firefox/91.0

Steps to reproduce:

1. Install the 'WenQuanYi Zen Hei Sharp' font. On debian/ubuntu, the commandline is apt install fonts-wqy-zenhei

2. Please test this page
   <pre style="font-family: 'WenQuanYi Zen Hei Sharp'; font-size: 16px">HelloWorld ABCDEFG 1234567 16px</pre>
   <pre style="font-family: 'WenQuanYi Zen Hei Sharp'; font-size: 15.5px">HelloWorld ABCDEFG 1234567 15.5px</pre>
   <pre style="font-family: 'WenQuanYi Zen Hei Sharp'; font-size: 15px">HelloWorld ABCDEFG 1234567 15px</pre>

Actual results:

The line in the middle (15.5px) is blurry. It seems the bitmap glyph is scaled.

Expected results:

The line in the middle (15.5px) should fallback to nearest font-size and be pixel perfect.

Comment 1

[Zhang Boyang]

Attachment: firefox91.13.0esr_xrender.png

Comment 2

[Zhang Boyang]

Attachment: firefox91.13.0esr_normal.png

Comment 3

[Zhang Boyang]

This bug also affects the UI of firefox. The text on UI is blurry, too. This problem doesn't exist in the old gfx.xrender.

The 'WenQuanYi Zen Hei Sharp' is a scalable font with embedded bitmaps. Similar fonts like 'SimSun', 'MS Gothic' is also affected.

Comment 4

[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 correct in case you think the bot is wrong.

Comment 5

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

The severity field is not set for this bug.
:dholbert, could you have a look please?

For more information, please visit auto_nag documentation.

Comment 6

[David Shin[:dshin]]

So, if it's a scalable font, but with embedded bitmaps, disabling embedded bitmaps at system-level may just resolve this.
This confers the advantage of not falling back to nearest sizes (Which I imagine we did, instead of scaling and then anti-aliasing) as well.

Comment 7

[Zhang Boyang]

(In reply to David Shin[:dshin] from comment #6)

So, if it's a scalable font, but with embedded bitmaps, disabling embedded bitmaps at system-level may just resolve this.
This confers the advantage of not falling back to nearest sizes (Which I imagine we did, instead of scaling and then anti-aliasing) as well.

Thanks for replying. Disabling bitmap fonts can be a workaround to this problem, but there are many people prefer bitmap fonts, especially for East-Asian scripts, because East-Asian characters are complex and bitmap fonts can improve readability greatly. So I think we'd better fix the problem.

I tested the same font on Firefox/Windows, and it doesn't have the problem. Old Firefox/Linux versions using xrender also doesn't have this problem. It seems only Firefox/Linux (with WebRenderer) is affected. (macOS is not tested, though)

On the other hand, Chrome/Linux and Chrome/Windows also don't have this problem.

Comment 8

[David Shin[:dshin]]

Attachment: Mimimum Reproducible Case, for Windows

[...] especially for East-Asian scripts, because East-Asian characters are complex and bitmap fonts can improve readability greatly. [...]

Haven't thought of that - thanks. Confirmed the rounding behaviour on Windows.