certain Arabic feature tags do not function

[BOBT]

Hello,

I'm working with an Arabic font in FL 5.0.4. Certain feature tags such as medi, init, fina, isol do not function while testing them. If I change the tag to be "ss01" I achieve the desired results. Other tags, such as rlig, or ccmp work correctly.

Is this an issue with FL?

The generated font appears to be working correctly.

Thanks in advance.

Regards,
Bob

[Paul Hunt (Adobe)]

The Arabic contextual glyph features (init, medi, fina, isol) will not preview correctly in FontLab, instead FLS5 will preview these features as 1 to 1 replacements. However, FontLab can export fonts with these features that will work correctly in applications that handle these features correctly, for example: MS Word or ME versions of Adobe products (or even Adobe CS4+ products with the help of World Ready templates).

[Adam Twardoch (FontLab)]

Indeed, the OpenType Layout engine used to preview OpenType Layout features within FontLab Studio is very simple, and does not "know" any of the shaping rules for complex scripts. Each complex script (Arabic, Devanagari, Bengali etc.) has a special set of rules that need to be applied to the text outside of the font in order to make it work correctly. FontLab Studio does not implement those rules. Many of the "real" OpenType Layout engines, such as Microsoft Uniscribe, do implement them, while others, such as Apple ATSUI, do not.

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