AAT Insertion With SetMark On Same Transition
Originator: | sascha.brawer | ||
Number: | rdar://44861764 | Date Originated: | 2018-09-28 |
Status: | Open | Resolved: | |
Product: | macOS | CoreGraphics | Product Version: | 10.13.6 |
Classification: | Reproducible: | Always |
CoreText on macOS 10.13.6 seems to have a bug when rendering fonts whose AAT finite-state table carries the SetMark flag on the same transition that also inserts a sequence of glyphs. See test case MORX-31 in Unicode’s test suite for text rendering engines. https://rawgit.com/unicode-org/text-rendering-tests/master/reports/CoreText.html#MORX-31 Compare to HarfBuzz: https://rawgit.com/unicode-org/text-rendering-tests/master/reports/FreeStack.html#MORX-31 To reproduce, see: https://github.com/unicode-org/text-rendering-tests Or render the test strings (XXAYYBZZ, etc.) with this font: https://github.com/unicode-org/text-rendering-tests/raw/master/fonts/TestMORXThirtyone.ttf
Comments
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Reply from Apple: “contextual and insertion subtables mark the first glyph (according to process order) before doing anything else. Since this behavior appears to go back to 1995 or so, I can’t change it but will use your bug to update the AAT documentation”