485244 - CoreText rendering loses glyphs when diacritic composition occurs across intervening diacritic

Status: RESOLVED WORKSFORME

(Core :: Graphics, defect)

Description

[Jonathan Kew [:jfkthame]]

Attachment: sample showing CoreText vanishing-character issue

When using CoreText rendering (see bug 389074), characters can go missing from the rendered text. This occurs when the text contains a base character followed by multiple diacritics, and the base can combine with a diacritic *other than the first one* to form a precomposed glyph.

This is a bug in CoreText, reported to Apple as rdar://6720723. To work around it, we could apply NFC normalization to the text before passing it to the CoreText APIs, but it is not clear that the issue is important enough to warrant this at the moment, as such data will probably not occur in normal web pages.

A sample file is attached. In each line, the two accented versions of "figure" should look the same; they differ only in diacritic ordering. With CoreText, in one case on each line, the base character will disappear and the diacritics appear to follow the preceding letter. This does not occur with ATSUI rendering. (However, note that when the diacritics are ordered such that the "disappearance" doesn't happen, CoreText often does a better job of positioning them.)

Comment 1

[Benoit Girard (:BenWa)]

This is no longer reproducible on 10.6.7. Please reopen if this is still an issue.