I am designing an Arabic opentype font. I use marks for placing Harakat, I have a problem when placing character U+06D6 (small sad with lam ligature) over U+06E4 (arabic small high madda). It is rendered incorrectly and SMALL-SAD-WITH-LAM is placed on an unknown place holder (the circle) instead of sitting on Madda, please check attached shot.
There are several places where things can go wrong here:
- Did you create an OpenType feature that performs this placement?
- Does whatever program you use for rendering support the OpenType feature you used to implement this?
- Are you using the characters in the right, Unicode-compliant order?
I know next to nothing about Arabic, but it seems to me that the desired output should be a combination of three characters:
- U+0628 Arabic letter beh
- U+06E4 Arabic small high madda
- U+06D6 Arabic small high ligature sad with lam with alef maksura
In the above order (from right to left), i.e. بۤۖ, they render without placeholders on my machine and it looks okay (as far as I can tell).