Did anybody do RTL kerning successfully in Glyphs? My first attempt failed and while I’m trying to do it in a different way, I wonder if there is a tried and tested way to do it. I saw few topics on this subject but no clear answer and those topics are rather old and the forum notification discouraged me to revive them!
FontLab also had a problem with RTL kerning and despite several attempt to fix it, the problem persisted as much as I remember. It seems to be a a tricky problem partially because it is very hard to test it in Arabic text flow [with Hebrew should be easier].
Here is the rough idea about what seems to be the problem:
You apply kerning between B and C. Suppose positive value and ‘ABC’ turns to ‘AB C’.
To do this, you apply the positive kerning value to the right side bearing of the first glyph.
In RTL this kerning amount should be applied to the left side bearing of the first glyph.
It doesn’t matter in which direction we preview the characters in Glyphs, no matter which direction, we still put the appropriate left side bearing of one beside the right side bearing of the other. The main issue is which character is considered first and the kerning is applied to the right side bearing of it, regardless the kerning pair is LTR or RTL. In other words for that kerned ‘AB C’ sample the positive value kerning is applied to the wrong side of B in RTL context. Something like ‘A BC’