About the problem that Khmer is displayed strangely in a web browser in certain situations

Kazunari Tsuboi

I encountered a strange phenomenon when displaying Khmer in web browsers.

I am not sure where to report the problem as I am not sure if it is the font, the browser or the operating system that is causing this problem.

Have you guys experienced this kind of problem before? What do you think is the cause?

Cases where the problem occurs

Windows 10, Chromebook (does not occur on iOS)

The same problem occurs in Chrome, Edge, and Firefox.

I confirmed the problem when I used Noto{Sans,Serif}Khmer and DaunPenh.

No problem when using Khmer UI

Problem Details

Diacritics are incorrectly positioned when certain strings are repeated four times.

When repeated more than 5 times, the position of the diacritic shifts.

The image uses 'ខ្លាំ'.

It can be reproduced with another string as long as it is a combination of a consonant, a subscripted consonant, and a vowel on the right side.

Sérgio Martins

A similar issue was reported in this twitter thread; It turned to be a bug in Harfbuzz. Does it happen in the latest update of Chrome Canary? If not, it would be reasonable to assume the issues are related.

Kazunari Tsuboi

I've confirmed that the latest version of Chrome Canary solves the problem!
It was a bug in Harfbuzz. Thanks for the great information.
I'll be waiting for the retail version of Chrome to fix the issue.

In this case I thought about the relationship between a particular product and the OpenType Shaping Engine.

This is the information that I feel is close to my understanding at the moment.
https://github.com/typotheque/text-shaping/blob/main/docs/otl.md

However, the Shaping Engine used by Chrome and Firefox running on iOS looks like Core Text instead of his Harfbuzz.
Is it correct to understand that "Chrome" doesn't necessarily use Harfbuzz?

Florian Pircher

Kazunari Tsuboi said:

However, the Shaping Engine used by Chrome and Firefox running on iOS looks like Core Text instead of his Harfbuzz.
Is it correct to understand that "Chrome" doesn't necessarily use Harfbuzz?

All browsers on iOS use (must use!) the WebKit framework for rendering web content. WebKit uses Core Text (at least on iOS) for fonts, so no iOS browser is using HarfBuzz.

Kazunari Tsuboi

Thank you very much. My confusion has been resolved a bit.
I often get confused by the relationship between the browser, the rendering engine, and the shaping engine.
But it's exciting to see many engineers working together to solve the problem.
Thank you for your kind information.