Bug 207754 – WebKit 606+ does not render KaTeX fraction lines

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Axel Howind]

Created attachment 390749 [details]
minimal HTML file exposing the rendering issue

When KaTeX is used with a webkit version >= 606, fraction lines do not render correctly.

This is independent of the operating system used. On the KaTeX side, this is tracked under https://github.com/KaTeX/KaTeX/issues/1775. After spending much time investigating, the bug seems to be on the webkit side. I myself have tried different versions of the JavaFX WebView component on Windows, MacOS and Linux, which are all based on a WebKit version of 606 or newer, and none renders fraction lines correctly. Linux users of WebKitGTK+ have also reported this bug.

Since Safari renders correctly, I checked Safari's WebKit version and asked a WebKitGTK+ user to test with that specific version and got this reply:
~~~
I use WebKitGTK+ in Ubuntu. Version WebKit engine is 605.1.15 (Mozilla/5.0 (X11; Ubuntu; Linux x86_64) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.0 Safari/605.1.15). The engine the \frac-line displays correct.
~~~

So this seems really to be a regression from WebKit 605.x to 606+.

[Axel Howind]

Created attachment 390750 [details]
example rendered using WebKit 608 (missing fraction line)

[Axel Howind]

Created attachment 390751 [details]
example rendered using WebKit 605.1.15 showing fraction line

[Ahmad Saleem]

I am unable to reproduce this issue on Safari 17.1, should we close this?

[Karl Dubost]

Thanks Ahmad!

[Axel Howind]

I am also unable to reproduce this using Safari 17.1. However the User agent string tells me that Safari is still using an older version of Webkit (605.1.15):

User Agent:Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.1 Safari/605.1.15

But the issue is still there if I use a newer version of WebKit:
User Agent:Mozilla/5.0 (Macintosh; PPC Mac OS X) AppleWebKit/616.1 (KHTML, like Gecko) JavaFX/21 Safari/616.1

[Axel Howind]

I somewhat doubt that Safari user agent string does not report the correct version as 605.1.15 seems rather outdated. I also get an even older version when checking the user agent string on my iphone where according to wikipedia 616.2.9 should be the actual version.

I just installed Gnome Web on Linux, and it displays correctly (though that one is also showing an outdated webkit version).

So, it seems you are right that this is not really a WebKit problem. Please ignore my reopening. I will look into whether it's caused somehow by JavaFX or maybe KaTeX does something weird based on the user agent string.

[Karl Dubost]

The user agent string is not related at all. And has nothing to do with rendering. 
The reason why you see the UA string having a different number than what you would expect is because of freezing parts of the UA to reduce fingerprinting.

[Axel Howind]

OpenJDK (JavaFX) bug: https://bugs.java.com/bugdatabase/view_bug?bug_id=JDK-8321313