[Webkit-unassigned] [Bug 135510] New: Incorrect rendering of Unicode combining half marks on OS X

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=135510

           Summary: Incorrect rendering of Unicode combining half marks on
                    OS X
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Macintosh
               URL: http://chris.improbable.org/experiments/browser/combin
                    ing-half-marks/
        OS/Version: Mac OS X 10.9
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: chris at improbable.org


One of our users reported a problem with the text displayed on http://www.wdl.org/en/item/10643/. The author name on that page uses the Unicode combining half marks COMBINING LIGATURE LEFT HALF and COMBINING LIGATURE RIGHT HALF (U+FE20, U+FE21)

According to the Unicode 6.0 specification – see page 235-236 of http://www.unicode.org/versions/Unicode6.0.0/ch07.pdf – two adjacent marks should combine into a single curve. 

On OS X, the behaviour depends whether font substitution occurred so e.g. the current WebKit Nightly will display the tests at http://chris.improbable.org/experiments/browser/combining-half-marks/ correctly only for Arial but most other fonts will display incorrectly. 

Recent versions of Internet Explorer on Windows 7 or later display correctly in all cases. Chrome and Firefox are also inconsistent depending on the OS and font combinations.

Previously reported to Apple as rdar://13105608

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