Bug 251753

Summary: Disconnected Arabic glyphs for embolden webfont
Product: WebKit Reporter: Ebrahim Byagowi <ebrahim>
Component: TextAssignee: Nobody <webkit-unassigned>
Status: NEW ---    
Severity: Normal CC: karlcow, mmaxfield, webkit-bug-importer, zalan
Priority: P2 Keywords: BrowserCompat, InRadar
Version: Safari Technology Preview   
Hardware: Unspecified   
OS: Unspecified   
Attachments:
Description Flags
Disconnected Arabic glyphs none

Description Ebrahim Byagowi 2023-02-05 00:17:58 PST 
Created attachment 464847 [details]
Disconnected Arabic glyphs

Happens in both tip of tree WebKit (6c4c9810) and Safari 16.2

1. Open https://datehijri.com/ (or its archive here https://web.archive.org/web/20230121054820/https://datehijri.com/ )
2. Pinch to zoom on the green colored text below

Actual:
It has disconnected Arabic glyphs.

Expected:
Like Firefox and Chrome, not disconnected Arabic glyphs
Comment 1 Ebrahim Byagowi 2023-02-05 13:22:53 PST 
Guess this is rather a CoreText bug than WebKit
Comment 2 zalan 2023-02-05 15:51:05 PST 
I noticed that some of the text (e.g. لتاريخ الميلادي:) was split into multiple runs and we painted them individually. Sometimes (incorrect) mismatching rounding directions could manifest in such subpixel gaps. However, after force-merging them all (so that لتاريخ الميلادي comes out as one TextRun) I was still able to see those tiny gaps, so this very well be a CoreText bug as you said. Myles, what do you think?
Comment 3 Radar WebKit Bug Importer 2023-02-12 00:18:19 PST 
<rdar://problem/105352894>