I have downloaded a free trail of this software, and by evaluating it it’s quite nice, but has a few bugs… There is a bug in the undo feature (using Mac OS 10.8.4 here). It’s not the topic, for now…
The topic is, when I open to edit an Arabic font that renders nicely in my Cocoa app, and then change the Acsender, Descender, Cap-Height, or X-Height properties, the font no longer renders properly in the app. The glyph substitution no longer works, the characters are rendered separated from each other…
I tried to go to the font info and refresh the features list, but that didn’t seem to help much.
Currently, I have implemented a workaround by changing the properties of the English font to match the Arabic font, not the other way around. I’ll stick with this setup, for now.
Rendering of Arabic relies heaviely on OpenType features. The features are mostly generated automatically. This depends on the glyph names to determine what features to build. Did you check the tutorial about Arabic? This should get you started.
If you thing that is a lot trouble to change the vertical metrics, you are right. Glyphs is ment to build new fonts not do small changes on existing fonts.
You might have better results if you use FontTools/ttx. This is a python library and used from the command line but very powerful.
@Georg Thank you, I really appreciate your reply and honest referral to the appropriate app for my use case.