1320274 - ZWJ at bidi run boundaries do not always have an effect

Status: NEW

(Core :: Layout: Text and Fonts, defect, P3)

Description

[Khaled Hosny]

Attachment: Test HTML file

In the attached test file, the same string but different base direction shows different handling of the ZWJ at bidi run boundaries.

This is a follow up for https://github.com/w3c/i18n-discuss/issues/2

Comment 1

[Khaled Hosny]

Attachment: Current Firefox rendering

Comment 2

[Khaled Hosny]

Attachment: Current Chrome rendering

Comment 3

[Khaled Hosny]

Firefox and Chrome render the attached HTML differently, and both are wrong IMO.

Comment 4

[Xidorn Quan [:xidorn] UTC+10]

Attachment: Rendering of testcase on Firefox and Chrome on macOS

What versions of Firefox and Chrome are you using? And what OS are you using?

It seems to me Firefox and Chrome have the same rendering for the testcase on my machine, and different from the rendering in the images you uploaded.

The screenshot is showing Firefox Developer Edition 52.0a2 and Chrome Canary 57 on macOS Sierra. (And I see the same rendering from Firefox 50 and Chrome 54, which are the current release.

I'm not familiar with those glyphs. Is this the expected rendering?

Comment 5

[Khaled Hosny]

Attachment: Test HTML file

Comment 6

[Khaled Hosny]

Attachment: Current Firefox rendering

Comment 7

[Khaled Hosny]

Attachment: Current Chrome rendering

Comment 8

[Khaled Hosny]

I think the choice of Arabic letter was a bit unfortunate as some fonts try to be smart and render its isolated form differently. I updated the HTML file and the screenshots to use another Arabic letter. You may also want to install the Amiri font (https://github.com/khaledhosny/amiri-font/releases) to get the same font I’m using (which might be important on Mac since the default Arabic fonts are AAT not OpenType and might behave differently).

Comment 9

[Khaled Hosny]

From what I’m seeing, it seems that when the base direction is LTR, Firefox applies only the leading ZWJ while Chrome applies only the trailing one. When the base direction is RTL both get applied correctly.